多线程的几个小程序，诠释多线程的基本概念

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通过实现Runnable来实现多线程：

public class TestThread1{public static void main(String[] args){Runner1 r = new Runner1();Thread t = new Thread(r);t.start();//注意：t.run(); 是指方法调用，先执行Runner1()后，再往下执行。for(int i=200; i<300; i++){System.out.println("main--" + i);}}}class Runner1 implements Runnable{public void run(){for(int i=0; i<100; i++){System.out.println("Runner1--" + i);}}}

public class Test1 implements Runnable {@Overridepublic void run() {for (int i = 0; i < 10; i++) {System.out.println("Thread: " + i );try {Thread.sleep((int)Math.random() * 200);} catch (InterruptedException e) {e.printStackTrace();}  }}public static void main(String[] args) {Test1 t1 = new Test1();Thread t_1 = new Thread(t1);t_1.setName("aaa");t_1.start();for (int i = 0; i < 10; i++) {System.out.println("main: " + i );try {Thread.sleep((int)Math.random() * 200);} catch (InterruptedException e) {e.printStackTrace();}  }}}

通过继承Thread来实现多线程：

public class TestThread1{public static void main(String[] args){Runner1 r = new Runner1();r.start();for(int i=200; i<300; i++){System.out.println("main--" + i);}}}class Runner1 extends Thread{public void run(){for(int i=0; i<100; i++){System.out.println("Runner1--" + i);}}}

注意：继承了Thread，那么不用再new Thread来起线程，直接用Runner1.start()即可

通过Thread.join()方法来等待当前线程走完
下面的程序，如果join了，那么n就等于1000

public static volatile int n = 0;public void run() {for (int i = 0; i < 10; i++, n++)try {sleep(3); // 为了使运行结果更随机，延迟3毫秒} catch (Exception e) {}}public static void main(String[] args) throws Exception {Thread threads[] = new Thread[100];for (int i = 0; i < threads.length; i++)// 建立100个线程threads[i] = new Test4();for (int i = 0; i < threads.length; i++)// 运行刚才建立的100个线程threads[i].start();if (args.length > 0){for (int i = 0; i < threads.length; i++){// 100个线程都执行完后继续threads[i].join();}}System.out.println("n=" + Test4.n);}

在多线程中如何传递参数：
简单的是通过构造函数和set()来传值
复杂的是通过回调函数传值
下面的代码描述了回调传值的用法：

package com.mhm.test;public class Test5 extends Thread {private Work work;public Test5(Work work) {this.work = work;}public void run() {java.util.Random random = new java.util.Random();Data data = new Data();int n1 = random.nextInt(1000);int n2 = random.nextInt(2000);int n3 = random.nextInt(3000);work.process(data, n1, n2, n3); // 使用回调函数System.out.println(String.valueOf(n1) + "+" + String.valueOf(n2) + "+" + String.valueOf(n3) + "=" + data.value);}public static void main(String[] args) {Thread t1 = new Test5(new Work());Thread t2 = new Test5(new Work());Thread t3 = new Test5(new Work());t1.start();t2.start();t3.start();}}class Data {public int value = 0;}class Work {public void process(Data data, Integer... numbers) {for (int n : numbers) {data.value += n;}}}

这个程序可能会输出"NULL"：
因为线程可能还没有赋值就已经syso了。
解决办法是在start()后面加个join();

package com.mhm.test;public class Test6 extends Thread {private String value1;    private String value2;    public void run()    {        value1 = "通过成员变量返回数据";        value2 = "通过成员方法返回数据";    }    public static void main(String[] args) throws Exception    {    Test6 thread = new Test6();        thread.start();        System.out.println("value1:" + thread.value1);        System.out.println("value2:" + thread.value2);    }}

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