代码收藏家 java菜鸟教程学习（完整版）
java实例
一.Java 字符串
1.Java 实例 – 字符串比较
public class StringCompareEmp{
public static void main(String args[]){
String str = "Hello World";
String anotherString = "hello world";
Object objStr = str;
System.out.println( str.compareTo(anotherString) );
System.out.println( str.compareToIgnoreCase(anotherString) ); //忽略大小写
System.out.println( str.compareTo(objStr.toString()));
}
}
2.Java 实例 – 查找字符串最后一次出现的位置
public class SearchlastString {
public static void main(String[] args) {
String strOrig = "Hello world ,Hello Runoob";
int lastIndex = strOrig.lastIndexOf("Runoob");
if(lastIndex == - 1){
System.out.println("没有找到字符串 Runoob");
}else{
System.out.println("Runoob 字符串最后出现的位置： "+ lastIndex);
}
}
}
3.Java 实例 – 删除字符串中的一个字符
public class Main {
public static void main(String args[]) {
String str = "this is Java";
System.out.println(removeCharAt(str, 3));
}
public static String removeCharAt(String s, int pos) {
return s.substring(0, pos) + s.substring(pos + 1);
}
}
4.Java 实例 – 字符串替换
public class StringReplaceEmp{
public static void main(String args[]){
String str="Hello World";
System.out.println( str.replace( 'H','W' ) );
System.out.println( str.replaceFirst("He", "Wa") );
System.out.println( str.replaceAll("He", "Ha") );
}
}
5.Java 实例 – 字符串反转
public class StringReverseExample{
public static void main(String[] args){
String string="runoob";
String reverse = new StringBuffer(string).reverse().toString();
System.out.println("字符串反转前:"+string);
System.out.println("字符串反转后:"+reverse);
}
}
6.Java 实例 – 字符串查找
public class SearchStringEmp {
public static void main(String[] args) {
String strOrig = "Google Runoob Taobao";
int intIndex = strOrig.indexOf("Runoob");
if(intIndex == - 1){
System.out.println("没有找到字符串 Runoob");
}else{
System.out.println("Runoob 字符串位置 " + intIndex);
}
}
}
7.Java 实例 – 字符串分割
public class JavaStringSplitEmp {
public static void main(String args[]){
String str = "www-runoob-com";
String[] temp;
String delimeter = "-"; // 指定分割字符
temp = str.split(delimeter); // 分割字符串
// 普通 for 循环
for(int i =0; i < temp.length ; i++){
System.out.println(temp[i]);
System.out.println("");
}
System.out.println("------java for each循环输出的方法-----");
String str1 = "www.runoob.com";
String[] temp1;
String delimeter1 = "\\."; // 指定分割字符， . 号需要转义
temp1 = str1.split(delimeter1); // 分割字符串
for(String x : temp1){
System.out.println(x);
System.out.println("");
}
}
}
8.Java 实例 – 字符串分割(StringTokenizer)
import java.util.StringTokenizer;
public class Main {
public static void main(String[] args) {
String str = "This is String , split by StringTokenizer, created by runoob";
StringTokenizer st = new StringTokenizer(str);
System.out.println("----- 通过空格分隔 ------");
while (st.hasMoreElements()) {
System.out.println(st.nextElement());
}
System.out.println("----- 通过逗号分隔 ------");
StringTokenizer st2 = new StringTokenizer(str, ",");
while (st2.hasMoreElements()) {
System.out.println(st2.nextElement());
}
}
}
9.Java 实例 – 字符串小写转大写
public class StringToUpperCaseEmp {
public static void main(String[] args) {
String str = "string runoob";
String strUpper = str.toUpperCase();
System.out.println("原始字符串: " + str);
System.out.println("转换为大写: " + strUpper);
}
}
10.Java 实例 – 测试两个字符串区域是否相等
public class StringRegionMatch{
public static void main(String[] args){
String first_str = "Welcome to Microsoft";
String second_str = "I work with microsoft";
boolean match1 = first_str.
regionMatches(11, second_str, 12, 9);
boolean match2 = first_str.
regionMatches(true, 11, second_str, 12, 9); //第一个参数 true 表示忽略大小写区别
System.out.println("区分大小写返回值：" + match1);
System.out.println("不区分大小写返回值：" + match2);
}
}
11.Java 实例 – 字符串性能比较测试
public class StringComparePerformance{
public static void main(String[] args){
long startTime = System.currentTimeMillis();
for(int i=0;i<50000;i++){
String s1 = "hello";
String s2 = "hello";
}
long endTime = System.currentTimeMillis();
System.out.println("通过 String 关键词创建字符串"
+ " : "+ (endTime - startTime)
+ " 毫秒" );
long startTime1 = System.currentTimeMillis();
for(int i=0;i<50000;i++){
String s3 = new String("hello");
String s4 = new String("hello");
}
long endTime1 = System.currentTimeMillis();
System.out.println("通过 String 对象创建字符串"
+ " : " + (endTime1 - startTime1)
+ " 毫秒");
}
}
12.Java 实例 – 字符串优化
public class StringOptimization {
public static void main(String[] args){
String variables[] = new String[50000];
for( int i=0;i <50000;i++){
variables[i] = "s"+i;
}
long startTime0 = System.currentTimeMillis();
for(int i=0;i<50000;i++){
variables[i] = "hello";
}
long endTime0 = System.currentTimeMillis();
System.out.println("直接使用字符串： "+ (endTime0 - startTime0) + " ms" );
long startTime1 = System.currentTimeMillis();
for(int i=0;i<50000;i++){
variables[i] = new String("hello");
}
long endTime1 = System.currentTimeMillis();
System.out.println("使用 new 关键字：" + (endTime1 - startTime1) + " ms");
long startTime2 = System.currentTimeMillis();
for(int i=0;i<50000;i++){
variables[i] = new String("hello");
variables[i] = variables[i].intern();
}
long endTime2 = System.currentTimeMillis();
System.out.println("使用字符串对象的 intern() 方法: "
+ (endTime2 - startTime2)
+ " ms");
}
}
13.Java 实例 – 字符串格式化
import java.util.*;
public class StringFormat {
public static void main(String[] args){
double e = Math.E;
System.out.format("%f%n", e);
System.out.format(Locale.CHINA , "%-10.4f%n%n", e); //指定本地为中国（CHINA）
}
}
14.Java 实例 – 连接字符串
public class StringConcatenate {
public static void main(String[] args){
long startTime = System.currentTimeMillis();
for(int i=0;i<5000;i++){
String result = "This is"
+ "testing the"
+ "difference"+ "between"
+ "String"+ "and"+ "StringBuffer";
}
long endTime = System.currentTimeMillis();
System.out.println("字符串连接"
+ " - 使用 + 操作符 : "
+ (endTime - startTime)+ " ms");
long startTime1 = System.currentTimeMillis();
for(int i=0;i<5000;i++){
StringBuffer result = new StringBuffer();
result.append("This is");
result.append("testing the");
result.append("difference");
result.append("between");
result.append("String");
result.append("and");
result.append("StringBuffer");
}
long endTime1 = System.currentTimeMillis();
System.out.println("字符串连接"
+ " - 使用 StringBuffer : "
+ (endTime1 - startTime1)+ " ms");
}
}
二.Java 数组
1.Java 实例 – 数组排序及元素查找
import java.util.Arrays;
public class MainClass {
public static void main(String args[]) throws Exception {
int array[] = { 2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
Arrays.sort(array);
printArray("数组排序结果为", array);
int index = Arrays.binarySearch(array, 2);
System.out.println("元素 2 在第 " + index + " 个位置");
}
private static void printArray(String message, int array[]) {
System.out.println(message
+ ": [length: " + array.length + "]");
for (int i = 0; i < array.length; i++) {
if(i != 0){
System.out.print(", ");
}
System.out.print(array[i]);
}
System.out.println();
}
}
2.Java 实例 – 数组添加元素
import java.util.Arrays;
public class MainClass {
public static void main(String args[]) throws Exception {
int array[] = { 2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
Arrays.sort(array);
printArray("数组排序", array);
int index = Arrays.binarySearch(array, 1);
System.out.println("元素 1 所在位置（负数为不存在）："
+ index);
int newIndex = -index - 1;
array = insertElement(array, 1, newIndex);
printArray("数组添加元素 1", array);
}
private static void printArray(String message, int array[]) {
System.out.println(message
+ ": [length: " + array.length + "]");
for (int i = 0; i < array.length; i++) {
if (i != 0){
System.out.print(", ");
}
System.out.print(array[i]);
}
System.out.println();
}
private static int[] insertElement(int original[],
int element, int index) {
int length = original.length;
int destination[] = new int[length + 1];
System.arraycopy(original, 0, destination, 0, index);
destination[index] = element;
System.arraycopy(original, index, destination, index
+ 1, length - index);
return destination;
}
}
3.Java 实例 – 获取数组长度
public class Main {
public static void main(String args[]) {
String[][] data = new String[2][5];
System.out.println("第一维数组长度: " + data.length);
System.out.println("第二维数组长度: " + data[0].length);
}
}
4.Java 实例 – 数组反转
public class RunoobTest {
/* 反转数组*/
static void reverse(int a[], int n)
{
int[] b = new int[n];
int j = n;
for (int i = 0; i < n; i++) {
b[j - 1] = a[i];
j = j - 1;
}
/*输入反转数组*/
System.out.println("反转后数组是: \n");
for (int k = 0; k < n; k++) {
System.out.println(b[k]);
}
}
public static void main(String[] args)
{
int [] arr = {10, 20, 30, 40, 50};
reverse(arr, arr.length);
}
}
5.Java 实例 – 数组输出
public class Welcome {
public static void main(String[] args){
String[] runoobs = new String[3];
runoobs[0] = "菜鸟教程";
runoobs[1] = "菜鸟工具";
runoobs[2] = "菜鸟笔记";
for (int i = 0; i < runoobs.length; i++){
System.out.println(runoobs[i]);
}
}
}
6.Java 实例 – 数组获取最大和最小值
import java.util.Arrays;
import java.util.Collections;
public class Main {
public static void main(String[] args) {
Integer[] numbers = { 8, 2, 7, 1, 4, 9, 5};
int min = (int) Collections.min(Arrays.asList(numbers));
int max = (int) Collections.max(Arrays.asList(numbers));
System.out.println("最小值: " + min);
System.out.println("最大值: " + max);
}
}
7.Java 实例 – 数组合并
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class Main {
public static void main(String args[]) {
String a[] = { "A", "E", "I" };
String b[] = { "O", "U" };
List list = new ArrayList(Arrays.asList(a));
list.addAll(Arrays.asList(b));
Object[] c = list.toArray();
System.out.println(Arrays.toString(c));
}
}
8.Java 实例 – 数组填充
import java.util.*;
public class FillTest {
public static void main(String args[]) {
int array[] = new int[6];
Arrays.fill(array, 100);
for (int i=0, n=array.length; i < n; i++) {
System.out.println(array[i]);
}
System.out.println();
Arrays.fill(array, 3, 6, 50);
for (int i=0, n=array.length; i< n; i++) {
System.out.println(array[i]);
}
}
}
9.Java 实例 – 数组扩容
public class Main {
public static void main(String[] args) {
String[] names = new String[] { "A", "B", "C" };
String[] extended = new String[5];
extended[3] = "D";
extended[4] = "E";
System.arraycopy(names, 0, extended, 0, names.length);
for (String str : extended){
System.out.println(str);
}
}
}
10.Java 实例 – 查找数组中的重复元素
public class MainClass {
public static void main(String[] args)
{
int[] my_array = {1, 2, 5, 5, 6, 6, 7, 2, 9, 2};
findDupicateInArray(my_array);
}
public static void findDupicateInArray(int[] a) {
int count=0;
for(int j=0;j<a.length;j++) {
for(int k =j+1;k<a.length;k++) {
if(a[j]==a[k]) {
count++;
}
}
if(count==1)
System.out.println( "重复元素 : " + a[j] );
count = 0;
}
}
}
11.Java 实例 – 删除数组元素
import java.util.Arrays;
public class RunoobTest {
public static void main(String[] args) {
int[] oldarray = new int[] {3, 4, 5, 6, 7};// 原始数组
int num = 2; // 删除索引为 2 的元素，即删除第三个元素 5
int[] newArray = new int[oldarray.length-1];// 新数组，长度为原始数组减去 1
for(int i=0;i<newArray.length; i++) {
// 判断元素是否越界
if (num < 0 || num >= oldarray.length) {
throw new RuntimeException("元素越界... ");
}
//
if(i<num) {
newArray[i] = oldarray[i];
}
else {
newArray[i] = oldarray[i+1];
}
}
// 打印输出数组内容
System.out.println(Arrays.toString(oldarray));
oldarray = newArray;
System.out.println(Arrays.toString(oldarray));
}
}
12.Java 实例 – 数组差集
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
ArrayList objArray = new ArrayList();
ArrayList objArray2 = new ArrayList();
objArray2.add(0,"common1");
objArray2.add(1,"common2");
objArray2.add(2,"notcommon");
objArray2.add(3,"notcommon1");
objArray.add(0,"common1");
objArray.add(1,"common2");
objArray.add(2,"notcommon2");
System.out.println("array1 的元素" +objArray);
System.out.println("array2 的元素" +objArray2);
objArray.removeAll(objArray2);
System.out.println("array1 与 array2 数组差集为："+objArray);
}
}
13.Java 实例 – 数组交集
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
ArrayList objArray = new ArrayList();
ArrayList objArray2 = new ArrayList();
objArray2.add(0,"common1");
objArray2.add(1,"common2");
objArray2.add(2,"notcommon");
objArray2.add(3,"notcommon1");
objArray.add(0,"common1");
objArray.add(1,"common2");
objArray.add(2,"notcommon2");
System.out.println("array1 数组元素："+objArray);
System.out.println("array2 数组元素："+objArray2);
objArray.retainAll(objArray2);
System.out.println("array2 & array1 数组交集为："+objArray);
}
}
14.Java 实例 – 在数组中查找指定元素
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
ArrayList<String> objArray = new ArrayList<String>();
ArrayList<String> objArray2 = new ArrayList<String>();
objArray2.add(0,"common1");
objArray2.add(1,"common2");
objArray2.add(2,"notcommon");
objArray2.add(3,"notcommon1");
objArray.add(0,"common1");
objArray.add(1,"common2");
System.out.println("objArray 的数组元素："+objArray);
System.out.println("objArray2 的数组元素："+objArray2);
System.out.println("objArray 是否包含字符串common2? ： "
+objArray.contains("common2"));
System.out.println("objArray2 是否包含数组 objArray? ："
+objArray2.contains(objArray) );
}
}
15.Java 实例 – 判断数组是否相等
import java.util.Arrays;
public class Main {
public static void main(String[] args) throws Exception {
int[] ary = {1,2,3,4,5,6};
int[] ary1 = {1,2,3,4,5,6};
int[] ary2 = {1,2,3,4};
System.out.println("数组 ary 是否与数组 ary1相等? ："
+Arrays.equals(ary, ary1));
System.out.println("数组 ary 是否与数组 ary2相等? ："
+Arrays.equals(ary, ary2));
}
}
16.Java 实例 – 数组并集
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
public class Main {
public static void main(String[] args) throws Exception {
String[] arr1 = { "1", "2", "3" };
String[] arr2 = { "4", "5", "6" };
String[] result_union = union(arr1, arr2);
System.out.println("并集的结果如下：");
for (String str : result_union) {
System.out.println(str);
}
}
// 求两个字符串数组的并集，利用set的元素唯一性
public static String[] union(String[] arr1, String[] arr2) {
Set<String> set = new HashSet<String>();
for (String str : arr1) {
set.add(str);
}
for (String str : arr2) {
set.add(str);
}
String[] result = { };
return set.toArray(result);
}
}
三.Java 时间处理
1.Java 实例 – 格式化时间（SimpleDateFormat）
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main{
public static void main(String[] args){
Date date = new Date();
String strDateFormat = "yyyy-MM-dd HH:mm:ss";
SimpleDateFormat sdf = new SimpleDateFormat(strDateFormat);
System.out.println(sdf.format(date));
}
}
2.Java 实例 – 获取当前时间
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main{
public static void main(String[] args){
SimpleDateFormat sdf = new SimpleDateFormat();// 格式化时间
sdf.applyPattern("yyyy-MM-dd HH:mm:ss a");// a为am/pm的标记
Date date = new Date();// 获取当前时间
System.out.println("现在时间：" + sdf.format(date)); // 输出已经格式化的现在时间（24小时制）
}
}
3.Java 实例 – 获取年份、月份等
import java.util.Calendar;
public class Main {
public static void main(String[] args) {
Calendar cal = Calendar.getInstance();
int day = cal.get(Calendar.DATE);
int month = cal.get(Calendar.MONTH) + 1;
int year = cal.get(Calendar.YEAR);
int dow = cal.get(Calendar.DAY_OF_WEEK);
int dom = cal.get(Calendar.DAY_OF_MONTH);
int doy = cal.get(Calendar.DAY_OF_YEAR);
System.out.println("当期时间: " + cal.getTime());
System.out.println("日期: " + day);
System.out.println("月份: " + month);
System.out.println("年份: " + year);
System.out.println("一周的第几天: " + dow); // 星期日为一周的第一天输出为 1，星期一输出为 2，以此类推
System.out.println("一月中的第几天: " + dom);
System.out.println("一年的第几天: " + doy);
}
}
4.Java 实例 – 时间戳转换成时间
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main{
public static void main(String[] args){
Long timeStamp = System.currentTimeMillis(); //获取当前时间戳
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String sd = sdf.format(new Date(Long.parseLong(String.valueOf(timeStamp)))); // 时间戳转换成时间
System.out.println("格式化结果：" + sd);
SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy 年 MM 月 dd 日 HH 时 mm 分 ss 秒");
String sd2 = sdf2.format(new Date(Long.parseLong(String.valueOf(timeStamp))));
System.out.println("格式化结果：" + sd2);
}
}
四.Java 方法
1.Java 实例 – 方法重载
class MyClass {
int height;
MyClass() {
System.out.println("无参数构造函数");
height = 4;
}
MyClass(int i) {
System.out.println("房子高度为 " + i + " 米");
height = i;
}
void info() {
System.out.println("房子高度为 " + height + " 米");
}
void info(String s) {
System.out.println(s + ": 房子高度为 " + height + " 米");
}
}
public class MainClass {
public static void main(String[] args) {
MyClass t = new MyClass(3);
t.info();
t.info("重载方法");
//重载构造函数
new MyClass();
}
}
2.Java 实例 – 输出数组元素
public class MainClass {
public static void printArray(Integer[] inputArray) {
for (Integer element : inputArray){
System.out.printf("%s ", element);
System.out.println();
}
}
public static void printArray(Double[] inputArray) {
for (Double element : inputArray){
System.out.printf("%s ", element);
System.out.println();
}
}
public static void printArray(Character[] inputArray) {
for (Character element : inputArray){
System.out.printf("%s ", element);
System.out.println();
}
}
public static void main(String args[]) {
Integer[] integerArray = { 1, 2, 3, 4, 5, 6 };
Double[] doubleArray = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7 };
Character[] characterArray = { 'H', 'E', 'L', 'L', 'O' };
System.out.println("输出整型数组:");
printArray(integerArray);
System.out.println("\n输出双精度型数组:");
printArray(doubleArray);
System.out.println("\n输出字符型数组:");
printArray(characterArray);
}
}
3.Java 实例 – 汉诺塔算法
public class MainClass {
public static void main(String[] args) {
int nDisks = 3;
doTowers(nDisks, 'A', 'B', 'C');
}
public static void doTowers(int topN, char from, char inter, char to) {
if (topN == 1){
System.out.println("Disk 1 from "
+ from + " to " + to);
}else {
doTowers(topN - 1, from, to, inter);
System.out.println("Disk "
+ topN + " from " + from + " to " + to);
doTowers(topN - 1, inter, from, to);
}
}
}
4.Java 实例 – 斐波那契数列
public class MainClass {
public static void main(String[] args) {
for (int counter = 0; counter <= 10; counter++){
System.out.printf("Fibonacci of %d is: %d\n", counter, fibonacci(counter));
}
}
public static long fibonacci(long number) {
if ((number == 0) || (number == 1))
return number;
else
return fibonacci(number - 1) + fibonacci(number - 2);
}
}
5.Java 实例 – 阶乘
public class MainClass {
public static void main(String args[]) {
for (int counter = 0; counter <= 10; counter++){
System.out.printf("%d! = %d\n", counter,
factorial(counter));
}
}
public static long factorial(long number) {
if (number <= 1)
return 1;
else
return number * factorial(number - 1);
}
}
6.Java 实例 – 方法覆盖
public class Findareas{
public static void main (String []agrs){
Figure f= new Figure(10 , 10);
Rectangle r= new Rectangle(9 , 5);
Figure figref;
figref=f;
System.out.println("Area is :"+figref.area());
figref=r;
System.out.println("Area is :"+figref.area());
}
}
class Figure{
double dim1;
double dim2;
Figure(double a , double b) {
dim1=a;
dim2=b;
}
Double area() {
System.out.println("Inside area for figure.");
return(dim1*dim2);
}
}
class Rectangle extends Figure {
Rectangle(double a, double b) {
super(a ,b);
}
Double area() {
System.out.println("Inside area for rectangle.");
return(dim1*dim2);
}
}
7.Java 实例 – instanceOf 关键字用法
/*
author by runoob.com
Main.java
*/
import java.util.ArrayList;
import java.util.Vector;
public class Main {
public static void main(String[] args) {
Object testObject = new ArrayList();
displayObjectClass(testObject);
}
public static void displayObjectClass(Object o) {
if (o instanceof Vector)
System.out.println("对象是 java.util.Vector 类的实例");
else if (o instanceof ArrayList)
System.out.println("对象是 java.util.ArrayList 类的实例");
else
System.out.println("对象是 " + o.getClass() + " 类的实例");
}
}
8.Java 实例 – break 关键字用法
public class Main {
public static void main(String[] args) {
int[] intary = { 99,12,22,34,45,67,5678,8990 };
int no = 5678;
int i = 0;
boolean found = false;
for ( ; i < intary.length; i++) {
if (intary[i] == no) {
found = true;
break;
}
}
if (found) {
System.out.println(no + " 元素的索引位置在: " + i);
}
else {
System.out.println(no + " 元素不在数组中");
}
}
}
9.Java 实例 – continue 关键字用法
public class Main {
public static void main(String[] args) {
StringBuffer searchstr = new StringBuffer("hello how are you. ");
int length = searchstr.length();
int count = 0;
for (int i = 0; i < length; i++) {
if (searchstr.charAt(i) != 'h')
continue;
count++;
searchstr.setCharAt(i, 'h');
}
System.out.println("发现 " + count
+ " 个 h 字符");
System.out.println(searchstr);
}
}
10.Java 实例 – 标签(Label)
public class Main {
public static void main(String[] args) {
outerLoop:
for (int i = 0; i < 3; i++) {
innerLoop:
for (int j = 0; j < 3; j++) {
if (i == 1 && j == 1) {
break outerLoop; // 跳出外部循环
}
System.out.println("i: " + i + ", j: " + j);
}
}
}
}
11.Java 实例 – enum 和 switch 语句使用
enum Car {
lamborghini,tata,audi,fiat,honda
}
public class Main {
public static void main(String args[]){
Car c;
c = Car.tata;
switch(c) {
case lamborghini:
System.out.println("你选择了 lamborghini!");
break;
case tata:
System.out.println("你选择了 tata!");
break;
case audi:
System.out.println("你选择了 audi!");
break;
case fiat:
System.out.println("你选择了 fiat!");
break;
case honda:
System.out.println("你选择了 honda!");
break;
default:
System.out.println("我不知道你的车型。");
break;
}
}
}
12.Java 实例 – Enum（枚举）构造函数及方法的使用
enum Car {
lamborghini(900),tata(2),audi(50),fiat(15),honda(12);
private int price;
Car(int p) {
price = p;
}
int getPrice() {
return price;
}
}
public class Main {
public static void main(String args[]){
System.out.println("所有汽车的价格：");
for (Car c : Car.values())
System.out.println(c + " 需要 "
+ c.getPrice() + " 千美元。");
}
}
13.Java 实例 – for 和 foreach循环使用
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class Main
{
public static void main(String[] args)
{
int[] arr = {1, 2, 3, 4, 5};
System.out.println("----------使用 for 循环------------");
for(int i=0; i<arr.length; i++)
{
System.out.println(arr[i]);
}
System.out.println("---------使用 For-Each 循环-------------");
//增强的 for 循环 For-Each
for(int element:arr)
{
System.out.println(element);
}
System.out.println("---------For-Each 循环二维数组-------------");
//遍历二维数组
int[][] arr2 = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}} ;
for(int[] row : arr2)
{
for(int element : row)
{
System.out.println(element);
}
}
//以三种方式遍历集合 List
List<String> list = new ArrayList<String>();
list.add("Google");
list.add("Runoob");
list.add("Taobao");
System.out.println("----------方式1：普通for循环-----------");
for(int i = 0; i < list.size(); i++)
{
System.out.println(list.get(i));
}
System.out.println("----------方式2：使用迭代器-----------");
for(Iterator<String> iter = list.iterator(); iter.hasNext();)
{
System.out.println(iter.next());
}
System.out.println("----------方式3：For-Each 循环-----------");
for(String str: list)
{
System.out.println(str);
}
}
}
14.Java 实例 – Varargs 可变参数使用
public class Main {
static int sumvarargs(int... intArrays){
int sum, i;
sum=0;
for(i=0; i< intArrays.length; i++) {
sum += intArrays[i];
}
return(sum);
}
public static void main(String args[]){
int sum=0;
sum = sumvarargs(new int[]{10,12,33});
System.out.println("数字相加之和为: " + sum);
}
}
15.Java 实例 – 重载(overloading)方法中使用 Varargs
public class Main {
static void vaTest(int ... no) {
System.out.print("vaTest(int ...): "
+ "参数个数: " + no.length +" 内容: ");
for(int n : no)
System.out.print(n + " ");
System.out.println();
}
static void vaTest(boolean ... bl) {
System.out.print("vaTest(boolean ...) " +
"参数个数: " + bl.length + " 内容: ");
for(boolean b : bl)
System.out.print(b + " ");
System.out.println();
}
static void vaTest(String msg, int ... no) {
System.out.print("vaTest(String, int ...): " +
msg +"参数个数: "+ no.length +" 内容: ");
for(int n : no)
System.out.print(n + " ");
System.out.println();
}
public static void main(String args[]){
vaTest(1, 2, 3);
vaTest("测试: ", 10, 20);
vaTest(true, false, false);
}
}
五.打印图形
1.Java 实例 – 打印菱形
public class Diamond {
public static void main(String[] args) {
print(8); // 输出 8 行的菱形
}
public static void print(int size) {
if (size % 2 == 0) {
size++; // 计算菱形大小
}
for (int i = 0; i < size / 2 + 1; i++) {
for (int j = size / 2 + 1; j > i + 1; j--) {
System.out.print(" "); // 输出左上角位置的空白
}
for (int j = 0; j < 2 * i + 1; j++) {
System.out.print("*"); // 输出菱形上半部边缘
}
System.out.println(); // 换行
}
for (int i = size / 2 + 1; i < size; i++) {
for (int j = 0; j < i - size / 2; j++) {
System.out.print(" "); // 输出菱形左下角空白
}
for (int j = 0; j < 2 * size - 1 - 2 * i; j++) {
System.out.print("*"); // 输出菱形下半部边缘
}
System.out.println(); // 换行
}
}
}
2.Java 实例 – 九九乘法表
public class MultiplicationTable {
public static void main(String[] args) {
for(int i=1;i<=9;i++) {
for(int j=1;j<=i;j++) {
System.out.print(j+"×"+i+"="+i*j+"\t");// \t 跳到下一个TAB位置
}
System.out.println();
}
}
}
3.Java 实例 – 打印三角形
class Demo{
public static void main(String[] args){
for(int i=1;i<=5;i++){
for(int j=5; i<=j; j--)
System.out.print(" ");
for(int j=1; j<=i; j++)
System.out.print("*");
for(int j=1; j<i; j++)
System.out.print("*");
System.out.println();
}
}
}
4.Java 实例 – 打印倒立的三角形
public class InvertedTriangle {
public static void main(String[] args) {
//打印倒立的三角形
for (int m = 1; m <= 4; m++) {
//打印空格
for (int n = 0; n <= m; n++) {
System.out.print(" ");
}
//打印*
for (int x = 1; x <= 7 -2 * (m - 1); x++) {
System.out.print("*");
}
System.out.println();
}
}
}
5.Java 实例 – 打印平行四边形
public class Parallelogram {
public static void main(String[] args) {
//外层循环 每次打出一个*
for (int i = 1; i <=5; i++) {
//填充空格
for (int j = 1; j <= 5 - i; j++) {
System.out.print(" ");
}
//内层循环 每次打印一个*
for (int k = 1; k <= 5; k++) {
System.out.print("*");
}
System.out.println();
}
}
}
6.Java 实例 – 打印矩形
public class Rect {
public static void main(String[] args) {
//外层循环 每次输出一行*
for (int i = 1; i <= 5; i++) {
System.out.print("*");
//内层循环 每次输出一个*
for (int j = 1; j <= 5; j++) {
System.out.print("*");
}
System.out.println();
}
}
}
六.Java 文件操作
1.Java 实例 – 文件写入
/*
author by runoob.com
Main.java
*/
import java.io.*;
public class Main {
public static void main(String[] args) {
try {
BufferedWriter out = new BufferedWriter(new FileWriter("runoob.txt"));
out.write("菜鸟教程");
out.close();
System.out.println("文件创建成功！");
} catch (IOException e) {
}
}
}
2.Java 实例 – 读取文件内容
import java.io.*;
public class Main {
public static void main(String[] args) {
try {
BufferedReader in = new BufferedReader(new FileReader("test.log"));
String str;
while ((str = in.readLine()) != null) {
System.out.println(str);
}
System.out.println(str);
} catch (IOException e) {
}
}
}
3.Java 实例 – 删除文件
import java.io.*;
public class Main
{
public static void main(String[] args)
{
try{
File file = new File("c:\\test.txt");
if(file.delete()){
System.out.println(file.getName() + " 文件已被删除！");
}else{
System.out.println("文件删除失败！");
}
}catch(Exception e){
e.printStackTrace();
}
}
}
4.Java 实例 – 将文件内容复制到另一个文件
import java.io.*;
public class Main {
public static void main(String[] args) throws Exception {
BufferedWriter out1 = new BufferedWriter(new FileWriter("srcfile"));
out1.write("string to be copied\n");
out1.close();
InputStream in = new FileInputStream(new File("srcfile"));
OutputStream out = new FileOutputStream
(new File("destnfile"));
byte[] buf = new byte[1024];
int len;
while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}
in.close();
out.close();
BufferedReader in1 = new BufferedReader(new FileReader("destnfile"));
String str;
while ((str = in1.readLine()) != null) {
System.out.println(str);
}
in1.close();
}
}
5.Java 实例 – 向文件中追加数据
import java.io.*;
public class Main {
public static void main(String[] args) throws Exception {
try {
BufferedWriter out = new BufferedWriter(new FileWriter("filename"));
out.write("aString1\n");
out.close();
out = new BufferedWriter(new FileWriter("filename",true));
out.write("aString2");
out.close();
BufferedReader in = new BufferedReader(new FileReader("filename"));
String str;
while ((str = in.readLine()) != null) {
System.out.println(str);
}
in.close();
}
catch (IOException e) {
System.out.println("exception occoured"+ e);
}
}
}
6.Java 实例 – 创建临时文件
import java.io.*;
public class Main {
public static void main(String[] args) throws Exception {
File temp = File.createTempFile("testrunoobtmp", ".txt");
System.out.println("文件路径: "+temp.getAbsolutePath());
temp.deleteOnExit();
BufferedWriter out = new BufferedWriter(new FileWriter(temp));
out.write("aString");
System.out.println("临时文件已创建:");
out.close();
}
}
7.Java 实例 – 修改文件最后的修改日期
import java.io.File;
import java.util.Date;
public class Main {
public static void main(String[] args) throws Exception {
File fileToChange = new File("C:/myjavafile.txt");
fileToChange.createNewFile();
Date filetime = new Date(fileToChange.lastModified());
System.out.println(filetime.toString());
System.out.println(fileToChange.setLastModified(System.currentTimeMillis()));
filetime = new Date(fileToChange.lastModified());
System.out.println(filetime.toString());
}
}
8.Java 实例 – 获取文件大小
import java.io.File;
public class Main {
public static long getFileSize(String filename) {
File file = new File(filename);
if (!file.exists() || !file.isFile()) {
System.out.println("文件不存在");
return -1;
}
return file.length();
}
public static void main(String[] args) {
long size = getFileSize("c:/java.txt");
System.out.println("java.txt文件大小为: " + size);
}
}
9.Java 实例 – 文件重命名
import java.io.File;
import java.io.IOException;
public class RunoobTest {
public static void main(String[] args) throws IOException {
// 旧的文件或目录
File oldName = new File("./runoob-test.txt");
// 新的文件或目录
File newName = new File("./runoob-test-2.txt");
if (newName.exists()) { // 确保新的文件名不存在
throw new java.io.IOException("file exists");
}
if(oldName.renameTo(newName)) {
System.out.println("已重命名");
} else {
System.out.println("Error");
}
}
}
10.Java 实例 – 设置文件只读
import java.io.File;
public class Main {
public static void main(String[] args) {
File file = new File("C:/java.txt");
System.out.println(file.setReadOnly());
System.out.println(file.canWrite());
}
}
11.Java 实例 – 检测文件是否存在
import java.io.File;
public class Main {
public static void main(String[] args) {
File file = new File("C:/java.txt");
System.out.println(file.exists());
}
}
12.Java 实例 – 在指定目录中创建文件
import java.io.File;
public class Main {
public static void main(String[] args) throws Exception {
File file = null;
File dir = new File("C:/");
file = File.createTempFile
("JavaTemp", ".javatemp", dir);
System.out.println(file.getPath());
}
}
13.Java 实例 – 获取文件修改时间
import java.io.File;
import java.util.Date;
public class Main {
public static void main(String[] args) {
File file = new File("Main.java");
Long lastModified = file.lastModified();
Date date = new Date(lastModified);
System.out.println(date);
}
}
14.Java 实例 – 创建文件
import java.io.File;
import java.io.IOException;
public class Main {
public static void main(String[] args) {
try{
File file = new File("C:/myfile.txt");
if(file.createNewFile())
System.out.println("文件创建成功！");
else
System.out.println("出错了，该文件已经存在。");
}
catch(IOException ioe) {
ioe.printStackTrace();
}
}
}
15.Java 实例 – 文件路径比较
import java.io.File;
public class Main {
public static void main(String[] args) {
File file1 = new File("C:/File/demo1.txt");
File file2 = new File("C:/java/demo1.txt");
if(file1.compareTo(file2) == 0) {
System.out.println("文件路径一致！");
} else {
System.out.println("文件路径不一致！");
}
}
}
七.Java 目录操作
1.Java 实例 – 递归创建目录
import java.io.File;
public class Main {
public static void main(String[] args) {
String directories = "D:\\a\\b\\c\\d\\e\\f\\g\\h\\i";
File file = new File(directories);
boolean result = file.mkdirs();
System.out.println("Status = " + result);
}
}
2.Java 实例 – 删除目录
import java.io.File;
public class Main {
public static void main(String[] argv) throws Exception {
// 删除当前目录下的 test 目录
deleteDir(new File("./test"));
}
public static boolean deleteDir(File dir) {
if (dir.isDirectory()) {
String[] children = dir.list();
for (int i = 0; i < children.length; i++) {
boolean success = deleteDir
(new File(dir, children[i]));
if (!success) {
return false;
}
}
}
if(dir.delete()) {
System.out.println("目录已被删除！");
return true;
} else {
System.out.println("目录删除失败！");
return false;
}
}
}
3.Java 实例 – 判断目录是否为空
import java.io.File;
public class Main
{
public static void main(String[] args)
{
File file = new File("./testdir"); // 当前目录下的 testdir目录
if(file.isDirectory()){
if(file.list().length>0){
System.out.println("目录不为空!");
}else{
System.out.println("目录为空!");
}
}else{
System.out.println("这不是一个目录!");
}
}
}
4.Java 实例 – 判断文件是否隐藏
import java.io.File;
public class Main {
public static void main(String[] args) {
File file = new File("C:/Demo.txt");
System.out.println(file.isHidden());
}
}
5.Java 实例 – 获取目录大小
import java.io.File;
import org.apache.commons.io.FileUtils;
public class Main {
public static void main(String[] args) {
long size = FileUtils.sizeOfDirectory(new File("C:/test"));
System.out.println("Size: " + size + " bytes");
}
}
6.Java 实例 – 在指定目录中查找文件
import java.io.File;
public class Main {
public static void main(String[] argv) throws Exception {
File dir = new File("../java");
String[] children = dir.list();
if (children == null) {
System.out.println("该目录不存在");
}
else {
for (int i = 0; i < children.length; i++) {
String filename = children[i];
System.out.println(filename);
}
}
}
}
7.Java 实例 – 获取文件的上级目录
import java.io.File;
public class Main {
public static void main(String[] args) {
File file = new File("C:/File/demo.txt");
String strParentDirectory = file.getParent();
System.out.println("文件的上级目录为 : " + strParentDirectory);
}
}
8.Java 实例 – 获取目录最后修改时间
import java.io.File;
import java.util.Date;
public class Main {
public static void main(String[] args) {
File file = new File("C://FileIO//demo.txt");
System.out.println("最后修改时间：" + new Date(file.lastModified()));
}
}
9.Java 实例 – 打印目录结构
import java.io.File;
import java.io.IOException;
public class FileUtil {
public static void main(String[] a)throws IOException{
showDir(1, new File("d:\\Java"));
}
static void showDir(int indent, File file) throws IOException {
for (int i = 0; i < indent; i++)
System.out.print('-');
System.out.println(file.getName());
if (file.isDirectory()) {
File[] files = file.listFiles();
for (int i = 0; i < files.length; i++)
showDir(indent + 4, files[i]);
}
}
}
10.Java 实例 – 遍历指定目录下的所有目录
import java.io.*;
class Main {
public static void main(String[] args) {
File dir = new File("F:");
File[] files = dir.listFiles();
FileFilter fileFilter = new FileFilter() {
public boolean accept(File file) {
return file.isDirectory();
}
};
files = dir.listFiles(fileFilter);
System.out.println(files.length);
if (files.length == 0) {
System.out.println("目录不存在或它不是一个目录");
}
else {
for (int i=0; i< files.length; i++) {
File filename = files[i];
System.out.println(filename.toString());
}
}
}
}
11.Java 实例 – 遍历指定目录下的所有文件
import java.io.File;
class Main {
public static void main(String[] args) {
File dir = new File("C:");
String[] children = dir.list();
if (children == null) {
System.out.println( "目录不存在或它不是一个目录");
}
else {
for (int i=0; i< children.length; i++) {
String filename = children[i];
System.out.println(filename);
}
}
}
}
12.Java 实例 – 在指定目录中查找文件
import java.io.*;
class Main {
public static void main(String[] args) {
File dir = new File("C:");
FilenameFilter filter = new FilenameFilter() {
public boolean accept
(File dir, String name) {
return name.startsWith("b");
}
};
String[] children = dir.list(filter);
if (children == null) {
System.out.println("目录不存在或它不是一个目录");
}
else {
for (int i=0; i < children.length; i++) {
String filename = children[i];
System.out.println(filename);
}
}
}
}
13.Java 实例 – 遍历系统根目录
import java.io.*;
class Main{
public static void main(String[] args){
File[] roots = File.listRoots();
System.out.println("系统所有根目录：");
for (int i=0; i < roots.length; i++) {
System.out.println(roots[i].toString());
}
}
}
14.Java 实例 – 查看当前工作目录
class Main {
public static void main(String[] args) {
String curDir = System.getProperty("user.dir");
System.out.println("你当前的工作目录为 :" + curDir);
}
}
15.Java 实例 – 遍历目录
import java.io.File;
public class Main {
public static void main(String[] argv) throws Exception {
System.out.println("遍历目录");
File dir = new File("/www/java"); //要遍历的目录
visitAllDirsAndFiles(dir);
}
public static void visitAllDirsAndFiles(File dir) {
System.out.println(dir);
if (dir.isDirectory()) {
String[] children = dir.list();
for (int i = 0; i < children.length; i++) {
visitAllDirsAndFiles(new File(dir, children[i]));
}
}
}
}
八.Java 异常处理
1.Java 实例 – 异常处理方法
class ExceptionDemo
{
public static void main(String[] args) {
try {
throw new Exception("My Exception");
} catch (Exception e) {
System.err.println("Caught Exception");
System.err.println("getMessage():" + e.getMessage());
System.err.println("getLocalizedMessage():" + e.getLocalizedMessage());
System.err.println("toString():" + e);
System.err.println("printStackTrace():");
e.printStackTrace();
}
}
}
2.Java 实例 – 多个异常处理（多个catch）
class Demo
{
int div(int a,int b) throws ArithmeticException,ArrayIndexOutOfBoundsException//在功能上通过throws的关键字声明该功能可能出现问题
{
int []arr = new int [a];
System.out.println(arr[4]);//制造的第一处异常
return a/b;//制造的第二处异常
}
}
class ExceptionDemo
{
public static void main(String[]args) //throws Exception
{
Demo d = new Demo();
try
{
int x = d.div(4,0);//程序运行截图中的三组示例 分别对应此处的三行代码
//int x = d.div(5,0);
//int x = d.div(4,1);
System.out.println("x="+x);
}
catch (ArithmeticException e)
{
System.out.println(e.toString());
}
catch (ArrayIndexOutOfBoundsException e)
{
System.out.println(e.toString());
}
catch (Exception e)//父类 写在此处是为了捕捉其他没预料到的异常 只能写在子类异常的代码后面
//不过一般情况下是不写的
{
System.out.println(e.toString());
}
System.out.println("Over");
}
}
3.Java 实例 – Finally的用法
public class ExceptionDemo2 {
public static void main(String[] argv) {
new ExceptionDemo2().doTheWork();
}
public void doTheWork() {
Object o = null;
for (int i=0; i<5; i++) {
try {
o = makeObj(i);
}
catch (IllegalArgumentException e) {
System.err.println
("Error: ("+ e.getMessage()+").");
return;
}
finally {
System.err.println("都已执行完毕");
if (o==null)
System.exit(0);
}
System.out.println(o);
}
}
public Object makeObj(int type)
throws IllegalArgumentException {
if (type == 1)
throw new IllegalArgumentException
("不是指定的类型： " + type);
return new Object();
}
}
4.Java 实例 – 使用 catch 处理异常
public class Main {
public static void main (String args[]) {
int array[]={20,20,40};
int num1=15,num2=10;
int result=10;
try{
result = num1/num2;
System.out.println("结果为 " +result);
for(int i =5;i >=0; i--) {
System.out.println ("数组的元素值为 " +array[i]);
}
}
catch (Exception e) {
System.out.println("触发异常 : "+e);
}
}
}
5.Java 实例 – 多线程异常处理
class MyThread extends Thread{
public void run(){
System.out.println("Throwing in " +"MyThread");
throw new RuntimeException();
}
}
class Main {
public static void main(String[] args){
MyThread t = new MyThread();
t.start();
try{
Thread.sleep(1000);
}
catch (Exception x){
System.out.println("Caught it" + x);
}
System.out.println("Exiting main");
}
}
6.Java 实例 – 获取异常的堆栈信息
public class Main{
public static void main (String args[]){
int array[]={20,20,40};
int num1=15,num2=10;
int result=10;
try{
result = num1/num2;
System.out.println("The result is" +result);
for(int i =5; i>=0; i--) {
System.out.println("The value of array is" +array[i]);
}
}
catch (Exception e) {
e.printStackTrace();
}
}
}
7.Java 实例 – 重载方法异常处理
public class Main {
double method(int i) throws Exception{
return i/0;
}
boolean method(boolean b) {
return !b;
}
static double method(int x, double y) throws Exception {
return x + y ;
}
static double method(double x, double y) {
return x + y - 3;
}
public static void main(String[] args) {
Main mn = new Main();
try{
System.out.println(method(10, 20.0));
System.out.println(method(10.0, 20));
System.out.println(method(10.0, 20.0));
System.out.println(mn.method(10));
}
catch (Exception ex){
System.out.println("exception occoure: "+ ex);
}
}
}
8.Java 实例 – 链试异常
public class Main {
public static void main (String args[])throws Exception {
int n=20,result=0;
try{
result=n/0;
System.out.println("结果为"+result);
}
catch(ArithmeticException ex){
System.out.println("发算术异常: "+ex);
try {
throw new NumberFormatException();
}
catch(NumberFormatException ex1) {
System.out.println("手动抛出链试异常 : "+ex1);
}
}
}
}
9.Java 实例 – 自定义异常
class WrongInputException extends Exception { // 自定义的类
WrongInputException(String s) {
super(s);
}
}
class Input {
void method() throws WrongInputException {
throw new WrongInputException("Wrong input"); // 抛出自定义的类
}
}
class TestInput {
public static void main(String[] args){
try {
new Input().method();
}
catch(WrongInputException wie) {
System.out.println(wie.getMessage());
}
}
}
九.Java 数据结构
1.Java 实例 – 数字求和运算
public class Main {
public static void main(String[] args) {
int limit=100;
int sum=0;
int i=1;
do
{
sum=sum+i;
i++;
}
while(i<=limit);
System.out.println("sum="+sum);
}
}
2.Java 实例 – 利用堆栈将中缀表达式转换成后缀
import java.io.IOException;
public class InToPost {
private Stack theStack;
private String input;
private String output = "";
public InToPost(String in) {
input = in;
int stackSize = input.length();
theStack = new Stack(stackSize);
}
public String doTrans() {
for (int j = 0; j < input.length(); j++) {
char ch = input.charAt(j);
switch (ch) {
case '+':
case '-':
gotOper(ch, 1);
break;
case '*':
case '/':
gotOper(ch, 2);
break;
case '(':
theStack.push(ch);
break;
case ')':
gotParen(ch);
break;
default:
output = output + ch;
break;
}
}
while (!theStack.isEmpty()) {
output = output + theStack.pop();
}
System.out.println(output);
return output;
}
public void gotOper(char opThis, int prec1) {
while (!theStack.isEmpty()) {
char opTop = theStack.pop();
if (opTop == '(') {
theStack.push(opTop);
break;
}
else {
int prec2;
if (opTop == '+' || opTop == '-')
prec2 = 1;
else
prec2 = 2;
if (prec2 < prec1) {
theStack.push(opTop);
break;
}
else
output = output + opTop;
}
}
theStack.push(opThis);
}
public void gotParen(char ch){
while (!theStack.isEmpty()) {
char chx = theStack.pop();
if (chx == '(')
break;
else
output = output + chx;
}
}
public static void main(String[] args)
throws IOException {
String input = "1+2*4/5-7+3/6";
String output;
InToPost theTrans = new InToPost(input);
output = theTrans.doTrans();
System.out.println("Postfix is " + output + '\n');
}
class Stack {
private int maxSize;
private char[] stackArray;
private int top;
public Stack(int max) {
maxSize = max;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
stackArray[++top] = j;
}
public char pop() {
return stackArray[top--];
}
public char peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
}
}
3.Java 实例 – 在链表（LinkedList）的开头和结尾
import java.util.LinkedList;
public class Main {
public static void main(String[] args) {
LinkedList<String> lList = new LinkedList<String>();
lList.add("1");
lList.add("2");
lList.add("3");
lList.add("4");
lList.add("5");
System.out.println(lList);
lList.addFirst("0");
System.out.println(lList);
lList.addLast("6");
System.out.println(lList);
}
}
4.Java 实例 – 获取链表（LinkedList）的第一个
import java.util.LinkedList;
public class Main {
public static void main(String[] args) {
LinkedList<String> lList = new LinkedList<String>();
lList.add("100");
lList.add("200");
lList.add("300");
lList.add("400");
lList.add("500");
System.out.println("链表的第一个元素是：" + lList.getFirst());
System.out.println("链表的最后一个元素是：" + lList.getLast());
}
}
5.Java 实例 – 删除链表中的元素
import java.util.*;
public class Main {
public static void main(String[] args) {
LinkedList<String> lList = new LinkedList<String>();
lList.add("1");
lList.add("8");
lList.add("6");
lList.add("4");
lList.add("5");
System.out.println(lList);
lList.subList(2, 4).clear();
System.out.println(lList);
}
}
6.Java 实例 – 获取链表的元素
import java.util.*;
public class Main {
private LinkedList list = new LinkedList();
public void push(Object v) {
list.addFirst(v);
}
public Object top() {
return list.getFirst();
}
public Object pop() {
return list.removeFirst();
}
public static void main(String[] args) {
Main stack = new Main();
for (int i = 30; i < 40; i++)
stack.push(new Integer(i));
System.out.println(stack.top());
System.out.println(stack.pop());
System.out.println(stack.pop());
System.out.println(stack.pop());
}
}
7.Java 实例 – 获取向量元素的索引值
import java.util.Collections;
import java.util.Vector;
public class Main {
public static void main(String[] args) {
Vector v = new Vector();
v.add("X");
v.add("M");
v.add("D");
v.add("A");
v.add("O");
Collections.sort(v);
System.out.println(v);
int index = Collections.binarySearch(v, "D");
System.out.println("元素索引值为 : " + index);
}
}
8.Java 实例 – 栈的实现
]`public class MyStack {
private int maxSize;
private long[] stackArray;
private int top;
public MyStack(int s) {
maxSize = s;
stackArray = new long[maxSize];
top = -1;
}
public void push(long j) {
stackArray[++top] = j;
}
public long pop() {
return stackArray[top--];
}
public long peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
public boolean isFull() {
return (top == maxSize - 1);
}
public static void main(String[] args) {
MyStack theStack = new MyStack(10);
theStack.push(10);
theStack.push(20);
theStack.push(30);
theStack.push(40);
theStack.push(50);
while (!theStack.isEmpty()) {
long value = theStack.pop();
System.out.print(value);
System.out.print(" ");
}
System.out.println("");
}
}`
9.Java 实例 – 链表元素查找
import java.util.LinkedList;
public class Main {
public static void main(String[] args) {
LinkedList lList = new LinkedList();
lList.add("1");
lList.add("2");
lList.add("3");
lList.add("4");
lList.add("5");
lList.add("2");
System.out.println("元素 2 第一次出现的位置：" + lList.indexOf("2"));
System.out.println("元素 2 最后一次出现的位置："+ lList.lastIndexOf("2"));
}
}
10.Java 实例 – 压栈出栈的方法实现字符串反转
import java.io.IOException;
public class StringReverserThroughStack {
private String input;
private String output;
public StringReverserThroughStack(String in) {
input = in;
}
public String doRev() {
int stackSize = input.length();
Stack theStack = new Stack(stackSize);
for (int i = 0; i < input.length(); i++) {
char ch = input.charAt(i);
theStack.push(ch);
}
output = "";
while (!theStack.isEmpty()) {
char ch = theStack.pop();
output = output + ch;
}
return output;
}
public static void main(String[] args)
throws IOException {
String input = "www.w3cschool.cc";
String output;
StringReverserThroughStack theReverser =
new StringReverserThroughStack(input);
output = theReverser.doRev();
System.out.println("反转前： " + input);
System.out.println("反转后： " + output);
}
class Stack {
private int maxSize;
private char[] stackArray;
private int top;
public Stack(int max) {
maxSize = max;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
stackArray[++top] = j;
}
public char pop() {
return stackArray[top--];
}
public char peek() {
return stackArray[top];
}
public boolean isEmpty() {
return (top == -1);
}
}
}
11.Java 实例 – 队列（Queue）用法
import java.util.LinkedList;
import java.util.Queue;
public class Main {
public static void main(String[] args) {
//add()和remove()方法在失败的时候会抛出异常(不推荐)
Queue<String> queue = new LinkedList<String>();
//添加元素
queue.offer("a");
queue.offer("b");
queue.offer("c");
queue.offer("d");
queue.offer("e");
for(String q : queue){
System.out.println(q);
}
System.out.println("===");
System.out.println("poll="+queue.poll()); //返回第一个元素，并在队列中删除
for(String q : queue){
System.out.println(q);
}
System.out.println("===");
System.out.println("element="+queue.element()); //返回第一个元素
for(String q : queue){
System.out.println(q);
}
System.out.println("===");
System.out.println("peek="+queue.peek()); //返回第一个元素
for(String q : queue){
System.out.println(q);
}
}
}
12.Java 实例 – 获取向量的最大元素
import java.util.Collections;
import java.util.Vector;
public class Main {
public static void main(String[] args) {
Vector v = new Vector();
v.add(new Double("3.4324"));
v.add(new Double("3.3532"));
v.add(new Double("3.342"));
v.add(new Double("3.349"));
v.add(new Double("2.3"));
Object obj = Collections.max(v);
System.out.println("最大元素是："+obj);
}
}
13.Java 实例 – 链表修改
import java.util.LinkedList;
public class Main {
public static void main(String[] a) {
LinkedList officers = new LinkedList();
officers.add("B");
officers.add("B");
officers.add("T");
officers.add("H");
officers.add("P");
System.out.println(officers);
officers.set(2, "M");
System.out.println(officers);
}
}
14.Java 实例 – 旋转向量
import java.util.Collections;
import java.util.Vector;
public class Main {
public static void main(String[] args) {
Vector<String> v = new Vector();
v.add("1");
v.add("2");
v.add("3");
v.add("4");
v.add("5");
System.out.println(v);
Collections.swap(v, 0, 4);
System.out.println("旋转后");
System.out.println(v);
}
}
十.Java 集合
1.Java 实例 – 数组转集合
import java.util.*;
import java.io.*;
public class ArrayToCollection{
public static void main(String args[])
throws IOException{
int n = 5; // 5 个元素
String[] name = new String[n];
for(int i = 0; i < n; i++){
name[i] = String.valueOf(i);
}
List<String> list = Arrays.asList(name);
System.out.println();
for(String li: list){
String str = li;
System.out.print(str + " ");
}
}
}
2.Java 实例 – 集合比较
import java.util.Collections;
import java.util.Set;
import java.util.TreeSet;
class Main {
public static void main(String[] args) {
String[] coins = { "Penny", "nickel", "dime", "Quarter", "dollar" };
Set<String> set = new TreeSet<String>();
for (int i = 0; i < coins.length; i++) {
set.add(coins[i]);
}
System.out.println(Collections.min(set));
System.out.println(Collections.min(set, String.CASE_INSENSITIVE_ORDER));
for (int i = 0; i <= 10; i++) {
System.out.print("-");
}
System.out.println("");
System.out.println(Collections.max(set));
System.out.println(Collections.max(set, String.CASE_INSENSITIVE_ORDER));
}
}
3.Java 实例 – HashMap遍历
import java.util.*;
public class Main {
public static void main(String[] args) {
HashMap< String, String> hMap =
new HashMap< String, String>();
hMap.put("1", "1st");
hMap.put("2", "2nd");
hMap.put("3", "3rd");
Collection cl = hMap.values();
Iterator itr = cl.iterator();
while (itr.hasNext()) {
System.out.println(itr.next());
}
}
}
4.Java 实例 – 集合长度
import java.util.*;
public class Main {
public static void main(String [] args) {
System.out.println( "集合实例!\n" );
int size;
HashSet collection = new HashSet ();
String str1 = "Yellow", str2 = "White", str3 =
"Green", str4 = "Blue";
Iterator iterator;
collection.add(str1);
collection.add(str2);
collection.add(str3);
collection.add(str4);
System.out.print("集合数据: ");
iterator = collection.iterator();
while (iterator.hasNext()){
System.out.print(iterator.next() + " ");
}
System.out.println();
size = collection.size();
if (collection.isEmpty()){
System.out.println("集合是空的");
}
else{
System.out.println( "集合长度: " + size);
}
System.out.println();
}
}
5.Java 实例 – 集合打乱顺序
import java.util.*;
public class Main {
public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 10; i++)
list.add(new Integer(i));
System.out.println("打乱前:");
System.out.println(list);
for (int i = 1; i < 6; i++) {
System.out.println("第" + i + "次打乱：");
Collections.shuffle(list);
System.out.println(list);
}
}
}
6.Java 实例 – 集合遍历
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
public class Main {
public static void main(String[] args) {
// List集合的遍历
listTest();
// Set集合的遍历
setTest();
}
private static void setTest() {
Set<String> set = new HashSet<String>();
set.add("JAVA");
set.add("C");
set.add("C++");
// 重复数据添加失败
set.add("JAVA");
set.add("JAVASCRIPT");
// 使用iterator遍历set集合
Iterator<String> it = set.iterator();
while (it.hasNext()) {
String value = it.next();
System.out.println(value);
}
// 使用增强for循环遍历set集合
for(String s: set){
System.out.println(s);
}
}
// 遍历list集合
private static void listTest() {
List<String> list = new ArrayList<String>();
list.add("菜");
list.add("鸟");
list.add("教");
list.add("程");
list.add("www.runoob.com");
// 使用iterator遍历
Iterator<String> it = list.iterator();
while (it.hasNext()) {
String value = it.next();
System.out.println(value);
}
// 使用传统for循环进行遍历
for (int i = 0, size = list.size(); i < size; i++) {
String value = list.get(i);
System.out.println(value);
}
// 使用增强for循环进行遍历
for (String value : list) {
System.out.println(value);
}
}
}
7.Java 实例 – 集合反转
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ListIterator;
class Main {
public static void main(String[] args) {
String[] coins = { "A", "B", "C", "D", "E" };
List l = new ArrayList();
for (int i = 0; i < coins.length; i++)
l.add(coins[i]);
ListIterator liter = l.listIterator();
System.out.println("反转前");
while (liter.hasNext())
System.out.println(liter.next());
Collections.reverse(l);
liter = l.listIterator();
System.out.println("反转后");
while (liter.hasNext())
System.out.println(liter.next());
}
}
8.Java 实例 – 删除集合中指定元素
import java.util.*;
public class Main {
public static void main(String [] args) {
System.out.println( "集合实例!\n" );
int size;
HashSet collection = new HashSet ();
String str1 = "Yellow", str2 = "White", str3 =
"Green", str4 = "Blue";
Iterator iterator;
collection.add(str1);
collection.add(str2);
collection.add(str3);
collection.add(str4);
System.out.print("集合数据: ");
iterator = collection.iterator();
while (iterator.hasNext()){
System.out.print(iterator.next() + " ");
}
System.out.println();
collection.remove(str2);
System.out.println("删除之后 [" + str2 + "]\n");
System.out.print("现在集合的数据是: ");
iterator = collection.iterator();
while (iterator.hasNext()){
System.out.print(iterator.next() + " ");
}
System.out.println();
size = collection.size();
System.out.println("集合大小: " + size + "\n");
}
}
9.Java 实例 – 只读集合
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
public class Main {
public static void main(String[] argv)
throws Exception {
List stuff = Arrays.asList(new String[] { "a", "b" });
List list = new ArrayList(stuff);
list = Collections.unmodifiableList(list);
try {
list.set(0, "new value");
}
catch (UnsupportedOperationException e) {
}
Set set = new HashSet(stuff);
set = Collections.unmodifiableSet(set);
Map map = new HashMap();
map = Collections.unmodifiableMap(map);
System.out.println("集合现在是只读");
}
}
10.Java 实例 – 集合输出
import java.util.*;
public class Main{
public static void main(String[] args) {
System.out.println("TreeMap 实例！\n");
TreeMap tMap = new TreeMap();
tMap.put(1, "Sunday");
tMap.put(2, "Monday");
tMap.put(3, "Tuesday");
tMap.put(4, "Wednesday");
tMap.put(5, "Thursday");
tMap.put(6, "Friday");
tMap.put(7, "Saturday");
System.out.println("TreeMap 键："
+ tMap.keySet());
System.out.println("TreeMap 值："
+ tMap.values());
System.out.println("键为 5 的值为: " + tMap.get(5)+ "\n");
System.out.println("第一个键: " + tMap.firstKey()
+ " Value: "
+ tMap.get(tMap.firstKey()) + "\n");
System.out.println("最后一个键: " + tMap.lastKey()
+ " Value: "+ tMap.get(tMap.lastKey()) + "\n");
System.out.println("移除第一个数据: "
+ tMap.remove(tMap.firstKey()));
System.out.println("现在 TreeMap 键为: "
+ tMap.keySet());
System.out.println("现在 TreeMap 包含: "
+ tMap.values() + "\n");
System.out.println("移除最后一个数据: "
+ tMap.remove(tMap.lastKey()));
System.out.println("现在 TreeMap 键为: "
+ tMap.keySet());
System.out.println("现在 TreeMap 包含: "
+ tMap.values());
}
}
11.Java 实例 – 集合转数组
import java.util.*;
public class Main{
public static void main(String[] args){
List<String> list = new ArrayList<String>();
list.add("菜");
list.add("鸟");
list.add("教");
list.add("程");
list.add("www.runoob.com");
String[] s1 = list.toArray(new String[0]);
for(int i = 0; i < s1.length; ++i){
String contents = s1[i];
System.out.print(contents);
}
}
}
12.Java 实例 – List 循环移动元素
import java.util.*;
public class Main {
public static void main(String[] args) {
List list = Arrays.asList("one Two three Four five six".split(" "));
System.out.println("List :"+list);
Collections.rotate(list, 3);
System.out.println("rotate: " + list);
}
}
13.Java 实例 – 查找 List 中的最大最小值
import java.util.*;
public class Main {
public static void main(String[] args) {
List list = Arrays.asList("one Two three Four five six one three Four".split(" "));
System.out.println(list);
System.out.println("最大值: " + Collections.max(list));
System.out.println("最小值: " + Collections.min(list));
}
}
14.Java 实例 – 遍历 HashTable 的键值
import java.util.Enumeration;
import java.util.Hashtable;
public class Main {
public static void main(String[] args) {
Hashtable ht = new Hashtable();
ht.put("1", "One");
ht.put("2", "Two");
ht.put("3", "Three");
Enumeration e = ht.keys();
while (e.hasMoreElements()){
System.out.println(e.nextElement());
}
}
}
15.Java 实例 – 使用 Enumeration 遍历 HashTable
import java.util.Enumeration;
import java.util.Hashtable;
public class Main {
public static void main(String[] args) {
Hashtable ht = new Hashtable();
ht.put("1", "One");
ht.put("2", "Two");
ht.put("3", "Three");
Enumeration e = ht.elements();
while(e.hasMoreElements()){
System.out.println(e.nextElement());
}
}
}
16.Java 实例 – 集合中添加不同类型元素
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
public class Main {
public static void main(String[] args) {
List lnkLst = new LinkedList();
lnkLst.add("element1");
lnkLst.add("element2");
lnkLst.add("element3");
lnkLst.add("element4");
displayAll(lnkLst);
List aryLst = new ArrayList();
aryLst.add("x");
aryLst.add("y");
aryLst.add("z");
aryLst.add("w");
displayAll(aryLst);
Set hashSet = new HashSet();
hashSet.add("set1");
hashSet.add("set2");
hashSet.add("set3");
hashSet.add("set4");
displayAll(hashSet);
SortedSet treeSet = new TreeSet();
treeSet.add("1");
treeSet.add("2");
treeSet.add("3");
treeSet.add("4");
displayAll(treeSet);
LinkedHashSet lnkHashset = new LinkedHashSet();
lnkHashset.add("one");
lnkHashset.add("two");
lnkHashset.add("three");
lnkHashset.add("four");
displayAll(lnkHashset);
Map map1 = new HashMap();
map1.put("key1", "J");
map1.put("key2", "K");
map1.put("key3", "L");
map1.put("key4", "M");
displayAll(map1.keySet());
displayAll(map1.values());
SortedMap map2 = new TreeMap();
map2.put("key1", "JJ");
map2.put("key2", "KK");
map2.put("key3", "LL");
map2.put("key4", "MM");
displayAll(map2.keySet());
displayAll(map2.values());
LinkedHashMap map3 = new LinkedHashMap();
map3.put("key1", "JJJ");
map3.put("key2", "KKK");
map3.put("key3", "LLL");
map3.put("key4", "MMM");
displayAll(map3.keySet());
displayAll(map3.values());
}
static void displayAll(Collection col) {
Iterator itr = col.iterator();
while (itr.hasNext()) {
String str = (String) itr.next();
System.out.print(str + " ");
}
System.out.println();
}
}
17.Java 实例 – List 元素替换
import java.util.*;
public class Main {
public static void main(String[] args) {
List list = Arrays.asList("one Two three Four five six one three Four".split(" "));
System.out.println("List :"+list);
Collections.replaceAll(list, "one", "hundrea");
System.out.println("replaceAll: " + list);
}
}
18.Java 实例 – List 截取
import java.util.*;
public class Main {
public static void main(String[] args) {
List list = Arrays.asList("one Two three Four five six one three Four".split(" "));
System.out.println("List :"+list);
List sublist = Arrays.asList("three Four".split(" "));
System.out.println("子列表 :"+sublist);
System.out.println("indexOfSubList: "
+ Collections.indexOfSubList(list, sublist));
System.out.println("lastIndexOfSubList: "
+ Collections.lastIndexOfSubList(list, sublist));
}
}
十一.Java 网络实例
1.Java 实例 – 获取指定主机的IP地址
import java.net.InetAddress;
import java.net.UnknownHostException;
public class GetIP {
public static void main(String[] args) {
InetAddress address = null;
try {
address = InetAddress.getByName("www.runoob.com");
}
catch (UnknownHostException e) {
System.exit(2);
}
System.out.println(address.getHostName() + "=" + address.getHostAddress());
System.exit(0);
}
}
2.Java 实例 – 查看端口是否已使用
import java.net.*;
import java.io.*;
public class Main {
public static void main(String[] args) {
Socket Skt;
String host = "localhost";
if (args.length > 0) {
host = args[0];
}
for (int i = 0; i < 1024; i++) {
try {
System.out.println("查看 "+ i);
Skt = new Socket(host, i);
System.out.println("端口 " + i + " 已被使用");
}
catch (UnknownHostException e) {
System.out.println("Exception occured"+ e);
break;
}
catch (IOException e) {
}
}
}
}
3.Java 实例 – 获取本机ip地址及主机名
import java.net.InetAddress;
import java.net.UnknownHostException;
public class NetworkInfo {
public static void main(String[] args) {
try {
// 获取本地主机对象
InetAddress localHost = InetAddress.getLocalHost();
// 获取主机名
String hostName = localHost.getHostName();
System.out.println("主机名: " + hostName);
// 获取IP地址
String hostAddress = localHost.getHostAddress();
System.out.println("IP地址: " + hostAddress);
} catch (UnknownHostException e) {
System.err.println("无法获取本机IP地址及主机名: " + e.getMessage());
e.printStackTrace();
}
}
}
4.Java 实例 – 获取远程文件大小
import java.net.URL;
import java.net.URLConnection;
public class Main {
public static void main(String[] args) throws Exception {
int size;
URL url = new URL("http://www.runoob.com/wp-content/themes/runoob/assets/img/newlogo.png");
URLConnection conn = url.openConnection();
size = conn.getContentLength();
if (size < 0)
System.out.println("无法获取文件大小。");
else
System.out.println("文件大小为：" + size + " bytes");
conn.getInputStream().close();
}
}
5.Java 实例 – Socket 实现多线程服务器程序
import java.io.*;
import java.net.*;
public class MultiThreadedServer {
public static void main(String[] args) {
int port = 12345; // 定义服务器端口
try (ServerSocket serverSocket = new ServerSocket(port)) {
System.out.println("服务器已启动，等待客户端连接...");
while (true) {
Socket clientSocket = serverSocket.accept(); // 接受客户端连接
System.out.println("客户端已连接: " + clientSocket.getInetAddress().getHostAddress());
// 为每个客户端连接启动一个新的线程
ClientHandler clientHandler = new ClientHandler(clientSocket);
new Thread(clientHandler).start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
class ClientHandler implements Runnable {
private Socket clientSocket;
public ClientHandler(Socket socket) {
this.clientSocket = socket;
}
@Override
public void run() {
try (
InputStream input = clientSocket.getInputStream();
OutputStream output = clientSocket.getOutputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(input));
PrintWriter writer = new PrintWriter(output, true)
) {
String clientMessage;
while ((clientMessage = reader.readLine()) != null) {
System.out.println("收到客户端消息: " + clientMessage);
writer.println("服务器回应: " + clientMessage); // 发送回应消息给客户端
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
clientSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
6.Java 实例 – 查看主机指定文件的最后修改时间
import java.net.URL;
import java.net.URLConnection;
import java.util.Date;
import java.text.SimpleDateFormat;
public class Main {
public static void main(String[] argv) throws Exception {
URL u = new URL("http://127.0.0.1/test/test.html");
URLConnection uc = u.openConnection();
SimpleDateFormat ft = new SimpleDateFormat ("yyyy-MM-dd hh:mm:ss");
uc.setUseCaches(false);
long timestamp = uc.getLastModified();
System.out.println("test.html 文件最后修改时间 :" + ft.format(new Date(timestamp)));
}
}
7.Java 实例 – 使用 Socket 连接到指定主机
import java.net.InetAddress;
import java.net.Socket;
public class WebPing {
public static void main(String[] args) {
try {
InetAddress addr;
Socket sock = new Socket("www.runoob.com", 80);
addr = sock.getInetAddress();
System.out.println("连接到 " + addr);
sock.close();
} catch (java.io.IOException e) {
System.out.println("无法连接 " + args[0]);
System.out.println(e);
}
}
}
8.Java 实例 – 网页抓取
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.InputStreamReader;
import java.net.URL;
public class Main {
public static void main(String[] args)
throws Exception {
URL url = new URL("http://www.runoob.com");
BufferedReader reader = new BufferedReader
(new InputStreamReader(url.openStream()));
BufferedWriter writer = new BufferedWriter
(new FileWriter("data.html"));
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
writer.write(line);
writer.newLine();
}
reader.close();
writer.close();
}
}
9.Java 实例 – 获取 URL响应头的日期信息
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Date;
public class Main{
public static void main(String args[])
throws Exception {
URL url = new URL("http://www.runoob.com");
HttpURLConnection httpCon =
(HttpURLConnection) url.openConnection();
long date = httpCon.getDate();
if (date == 0)
System.out.println("无法获取信息。");
else
System.out.println("Date: " + new Date(date));
}
}
10.Java 实例 – 获取 URL 响应头信息
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Map;
import java.util.Set;
public class Main {
public static void main(String[] args) throws IOException{
URL url = new URL("http://www.runoob.com");
URLConnection conn = url.openConnection();
Map headers = conn.getHeaderFields();
Set<String> keys = headers.keySet();
for( String key : keys ){
String val = conn.getHeaderField(key);
System.out.println(key+" "+val);
}
System.out.println( conn.getLastModified() );
}
}
11.Java 实例 – 解析 URL
import java.net.URL;
public class Main {
public static void main(String[] args)
throws Exception {
URL url = new URL("http://www.runoob.com/html/html-tutorial.html");
System.out.println("URL 是 " + url.toString());
System.out.println("协议是 " + url.getProtocol());
System.out.println("文件名是 " + url.getFile());
System.out.println("主机是 " + url.getHost());
System.out.println("路径是 " + url.getPath());
System.out.println("端口号是 " + url.getPort());
System.out.println("默认端口号是 "
+ url.getDefaultPort());
}
}
12.Java 实例 – ServerSocket 和 Socket 通信实例
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String[] args) {
try {
ServerSocket ss = new ServerSocket(8888);
System.out.println("启动服务器....");
Socket s = ss.accept();
System.out.println("客户端:"+s.getInetAddress().getLocalHost()+"已连接到服务器");
BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
//读取客户端发送来的消息
String mess = br.readLine();
System.out.println("客户端："+mess);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
bw.write(mess+"\n");
bw.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.Socket;
import java.net.UnknownHostException;
public class Client {
public static void main(String[] args) {
try {
Socket s = new Socket("127.0.0.1",8888);
//构建IO
InputStream is = s.getInputStream();
OutputStream os = s.getOutputStream();
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os));
//向服务器端发送一条消息
bw.write("测试客户端和服务器通信，服务器接收到消息返回到客户端\n");
bw.flush();
//读取服务器返回的消息
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String mess = br.readLine();
System.out.println("服务器："+mess);
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
十二.Java 线程
1.Java 实例 – 查看线程是否存活
public class TwoThreadAlive extends Thread {
public void run() {
for (int i = 0; i < 10; i++) {
printMsg();
}
}
public void printMsg() {
Thread t = Thread.currentThread();
String name = t.getName();
System.out.println("name=" + name);
}
public static void main(String[] args) {
TwoThreadAlive tt = new TwoThreadAlive();
tt.setName("Thread");
System.out.println("before start(), tt.isAlive()=" + tt.isAlive());
tt.start();
System.out.println("just after start(), tt.isAlive()=" + tt.isAlive());
for (int i = 0; i < 10; i++) {
tt.printMsg();
}
System.out.println("The end of main(), tt.isAlive()=" + tt.isAlive());
}
}
2.Java 实例 – 获取当前线程名称
public class TwoThreadGetName extends Thread {
public void run() {
for (int i = 0; i < 10; i++) {
printMsg();
}
}
public void printMsg() {
Thread t = Thread.currentThread();
String name = t.getName();
System.out.println("name=" + name);
}
public static void main(String[] args) {
TwoThreadGetName tt = new TwoThreadGetName();
tt.start();
for (int i = 0; i < 10; i++) {
tt.printMsg();
}
}
}
3.Java 实例 – 状态监测
class MyThread extends Thread{
boolean waiting= true;
boolean ready= false;
MyThread() {
}
public void run() {
String thrdName = Thread.currentThread().getName();
System.out.println(thrdName + " starting.");
while(waiting)
System.out.println("waiting:"+waiting);
System.out.println("waiting...");
startWait();
try {
Thread.sleep(1000);
}
catch(Exception exc) {
System.out.println(thrdName + " interrupted.");
}
System.out.println(thrdName + " terminating.");
}
synchronized void startWait() {
try {
while(!ready) wait();
}
catch(InterruptedException exc) {
System.out.println("wait() interrupted");
}
}
synchronized void notice() {
ready = true;
notify();
}
}
public class Main {
public static void main(String args[])
throws Exception{
MyThread thrd = new MyThread();
thrd.setName("MyThread #1");
showThreadStatus(thrd);
thrd.start();
Thread.sleep(50);
showThreadStatus(thrd);
thrd.waiting = false;
Thread.sleep(50);
showThreadStatus(thrd);
thrd.notice();
Thread.sleep(50);
showThreadStatus(thrd);
while(thrd.isAlive())
System.out.println("alive");
showThreadStatus(thrd);
}
static void showThreadStatus(Thread thrd) {
System.out.println(thrd.getName() + "Alive:=" + thrd.isAlive() + " State:=" + thrd.getState());
}
}
4.Java 实例 – 线程优先级设置
public class SimplePriorities extends Thread {
private int countDown = 5;
private volatile double d = 0;
public SimplePriorities(int priority) {
setPriority(priority);
start();
}
public String toString() {
return super.toString() + ": " + countDown;
}
public void run() {
while(true) {
for(int i = 1; i < 100000; i++)
d = d + (Math.PI + Math.E) / (double)i;
System.out.println(this);
if(--countDown == 0) return;
}
}
public static void main(String[] args) {
new SimplePriorities(Thread.MAX_PRIORITY);
for(int i = 0; i < 5; i++)
new SimplePriorities(Thread.MIN_PRIORITY);
}
}
5.Java 实例 – 死锁及解决方法
import java.util.Date;
public class LockTest {
public static String obj1 = "obj1";
public static String obj2 = "obj2";
public static void main(String[] args) {
LockA la = new LockA();
new Thread(la).start();
LockB lb = new LockB();
new Thread(lb).start();
}
}
class LockA implements Runnable{
public void run() {
try {
System.out.println(new Date().toString() + " LockA 开始执行");
while(true){
synchronized (LockTest.obj1) {
System.out.println(new Date().toString() + " LockA 锁住 obj1");
Thread.sleep(3000); // 此处等待是给B能锁住机会
synchronized (LockTest.obj2) {
System.out.println(new Date().toString() + " LockA 锁住 obj2");
Thread.sleep(60 * 1000); // 为测试，占用了就不放
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
class LockB implements Runnable{
public void run() {
try {
System.out.println(new Date().toString() + " LockB 开始执行");
while(true){
synchronized (LockTest.obj2) {
System.out.println(new Date().toString() + " LockB 锁住 obj2");
Thread.sleep(3000); // 此处等待是给A能锁住机会
synchronized (LockTest.obj1) {
System.out.println(new Date().toString() + " LockB 锁住 obj1");
Thread.sleep(60 * 1000); // 为测试，占用了就不放
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
6.Java 实例 – 获取线程id
public class Main extends Object implements Runnable {
private ThreadID var;
public Main(ThreadID v) {
this.var = v;
}
public void run() {
try {
print("var getThreadID =" + var.getThreadID());
Thread.sleep(2000);
print("var getThreadID =" + var.getThreadID());
} catch (InterruptedException x) {
}
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.out.println(name + ": " + msg);
}
public static void main(String[] args) {
ThreadID tid = new ThreadID();
Main shared = new Main(tid);
try {
Thread threadA = new Thread(shared, "threadA");
threadA.start();
Thread.sleep(500);
Thread threadB = new Thread(shared, "threadB");
threadB.start();
Thread.sleep(500);
Thread threadC = new Thread(shared, "threadC");
threadC.start();
} catch (InterruptedException x) {
}
}
}
class ThreadID extends ThreadLocal {
private int nextID;
public ThreadID() {
nextID = 10001;
}
private synchronized Integer getNewID() {
Integer id = new Integer(nextID);
nextID++;
return id;
}
protected Object initialValue() {
print("in initialValue()");
return getNewID();
}
public int getThreadID() {
Integer id = (Integer) get();
return id.intValue();
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.out.println(name + ": " + msg);
}
}
7.Java 实例 – 线程挂起
public class SleepingThread extends Thread {
private int countDown = 5;
private static int threadCount = 0;
public SleepingThread() {
super("" + ++threadCount);
start();
}
public String toString() {
return "#" + getName() + ": " + countDown;
}
public void run() {
while (true) {
System.out.println(this);
if (--countDown == 0)
return;
try {
sleep(100);
}
catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
}
public static void main(String[] args)
throws InterruptedException {
for (int i = 0; i < 5; i++)
new SleepingThread().join();
System.out.println("线程已被挂起");
}
}
8.Java 实例 – 终止线程
public class ThreadInterrupt extends Thread
{
public void run()
{
try
{
sleep(50000); // 延迟50秒
}
catch (InterruptedException e)
{
System.out.println(e.getMessage());
}
}
public static void main(String[] args) throws Exception
{
Thread thread = new ThreadInterrupt();
thread.start();
System.out.println("在50秒之内按任意键中断线程!");
System.in.read();
thread.interrupt();
thread.join();
System.out.println("线程已经退出!");
}
}
9.Java 实例 – 生产者/消费者问题
/*
author by runoob.com
ProducerConsumerTest.java
*/
public class ProducerConsumerTest {
public static void main(String[] args) {
CubbyHole c = new CubbyHole();
Producer p1 = new Producer(c, 1);
Consumer c1 = new Consumer(c, 1);
p1.start();
c1.start();
}
}
class CubbyHole {
private int contents;
private boolean available = false;
public synchronized int get() {
while (available == false) {
try {
wait();
}
catch (InterruptedException e) {
}
}
available = false;
notifyAll();
return contents;
}
public synchronized void put(int value) {
while (available == true) {
try {
wait();
}
catch (InterruptedException e) {
}
}
contents = value;
available = true;
notifyAll();
}
}
class Consumer extends Thread {
private CubbyHole cubbyhole;
private int number;
public Consumer(CubbyHole c, int number) {
cubbyhole = c;
this.number = number;
}
public void run() {
int value = 0;
for (int i = 0; i < 10; i++) {
value = cubbyhole.get();
System.out.println("消费者 #" + this.number+ " got: " + value);
}
}
}
class Producer extends Thread {
private CubbyHole cubbyhole;
private int number;
public Producer(CubbyHole c, int number) {
cubbyhole = c;
this.number = number;
}
public void run() {
for (int i = 0; i < 10; i++) {
cubbyhole.put(i);
System.out.println("生产者 #" + this.number + " put: " + i);
try {
sleep((int)(Math.random() * 100));
} catch (InterruptedException e) { }
}
}
}
10.Java 实例 – 获取线程状态
// Java 程序 - 演示线程状态
class thread implements Runnable
{
public void run()
{
// thread2 - 超时等待
try
{
Thread.sleep(1500);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
System.out.println("State of thread1 while it called join() method on thread2 -"+
Test.thread1.getState());
try
{
Thread.sleep(200);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
}
public class Test implements Runnable
{
public static Thread thread1;
public static Test obj;
public static void main(String[] args)
{
obj = new Test();
thread1 = new Thread(obj);
// 创建 thread1，现在是初始状态
System.out.println("State of thread1 after creating it - " + thread1.getState());
thread1.start();
// thread1 - 就绪状态
System.out.println("State of thread1 after calling .start() method on it - " +
thread1.getState());
}
public void run()
{
thread myThread = new thread();
Thread thread2 = new Thread(myThread);
// 创建 thread1，现在是初始状态
System.out.println("State of thread2 after creating it - "+ thread2.getState());
thread2.start();
// thread2 - 就绪状态
System.out.println("State of thread2 after calling .start() method on it - " +
thread2.getState());
// moving thread1 to timed waiting state
try
{
//moving - 超时等待
Thread.sleep(200);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
System.out.println("State of thread2 after calling .sleep() method on it - "+
thread2.getState() );
try
{
// 等待 thread2 终止
thread2.join();
}
catch (InterruptedException e)
{
e.printStackTrace();
}
System.out.println("State of thread2 when it has finished it's execution - " +
thread2.getState());
}
}
11.Java 实例 – 获取所有线程
public class Main extends Thread {
public static void main(String[] args) {
Main t1 = new Main();
t1.setName("thread1");
t1.start();
ThreadGroup currentGroup =
Thread.currentThread().getThreadGroup();
int noThreads = currentGroup.activeCount();
Thread[] lstThreads = new Thread[noThreads];
currentGroup.enumerate(lstThreads);
for (int i = 0; i < noThreads; i++)
System.out.println("线程号：" + i + " = " + lstThreads[i].getName());
}
}
12.Java 实例 – 查看线程优先级
public class Main extends Object {
private static Runnable makeRunnable() {
Runnable r = new Runnable() {
public void run() {
for (int i = 0; i < 5; i++) {
Thread t = Thread.currentThread();
System.out.println("in run() - priority="
+ t.getPriority()+ ", name=" + t.getName());
try {
Thread.sleep(2000);
}
catch (InterruptedException x) {
}
}
}
};
return r;
}
public static void main(String[] args) {
System.out.println("in main() - Thread.currentThread().getPriority()=" + Thread.currentThread().getPriority());
System.out.println("in main() - Thread.currentThread().getName()="+ Thread.currentThread().getName());
Thread threadA = new Thread(makeRunnable(), "threadA");
threadA.start();
try {
Thread.sleep(3000);
}
catch (InterruptedException x) {
}
System.out.println("in main() - threadA.getPriority()="+ threadA.getPriority());
}
}
13.Java 实例 – 中断线程
public class Main extends Object
implements Runnable {
public void run() {
try {
System.out.println("in run() - 将运行 work2() 方法");
work2();
System.out.println("in run() - 从 work2() 方法回来");
}
catch (InterruptedException x) {
System.out.println("in run() - 中断 work2() 方法");
return;
}
System.out.println("in run() - 休眠后执行");
System.out.println("in run() - 正常离开");
}
public void work2() throws InterruptedException {
while (true) {
if (Thread.currentThread().isInterrupted()) {
System.out.println("C isInterrupted()=" + Thread.currentThread().isInterrupted());
Thread.sleep(2000);
System.out.println("D isInterrupted()=" + Thread.currentThread().isInterrupted());
}
}
}
public void work() throws InterruptedException {
while (true) {
for (int i = 0; i < 100000; i++) {
int j = i * 2;
}
System.out.println("A isInterrupted()=" + Thread.currentThread().isInterrupted());
if (Thread.interrupted()) {
System.out.println("B isInterrupted()=" + Thread.currentThread().isInterrupted());
throw new InterruptedException();
}
}
}
public static void main(String[] args) {
Main si = new Main();
Thread t = new Thread(si);
t.start();
try {
Thread.sleep(2000);
}
catch (InterruptedException x) {
}
System.out.println("in main() - 中断其他线程");
t.interrupt();
System.out.println("in main() - 离开");
}
}
作者：IS evening
