多线程，实现两个线程加1，两个线程减1

package com.thread;

public class ThreadTest1 { private int j = 0;

 public static void main(String arg[]) {  ThreadTest1 tt = new ThreadTest1();  Run1 r1 = tt.new Run1();  Run2 r2 = tt.new Run2();  Run1 r3 = tt.new Run1();  Run2 r4 = tt.new Run2();

  r1.start();  r2.start();  r3.start();  r4.start();

 }

 class Run1 extends Thread {  public synchronized void run() {   for (int i = 0; i < 10; i++) {    System.out      .println(Thread.currentThread().getName() + ":" + j++);   }  } }

 class Run2 extends Thread {  public synchronized void run() {   for (int i = 0; i < 10; i++) {    System.out      .println(Thread.currentThread().getName() + ":" + j--);   }  } }}