Design 4 threads, two of which increase j by 1 each time, and the other two threads decrease j by 1 each time.

 1 package zzg;  2  3 public class ThreadTest {  4 private int j;  5 public static void main(String[] arge){  6 ThreadTest t1 = new ThreadTest();  7 Inc inc = t1.new Inc();  8 Dec dec = t1.new Dec();  9 for(int i=0;i<2;i++){ 10 Thread t = new Thread(inc); 11  t.start(); 12 t = new Thread(dec); 13  t.start(); 14  } 15 } 16 private synchronized void inc(){ 17 j++; 18 System.out.println(Thread.currentThread().getName() + "-inc:" + j); 19 } 20 private synchronized void dec(){ 21 j--; 22 System.out.println(Thread.currentThread().getName() + "-inc:" + j); 23 } 24 class Inc implements Runnable{ 25 public void run(){ 26 for(int i=0;i<100;i++){ 27  inc(); 28  } 29  } 30 } 31 class Dec implements Runnable{ 32 public void run(){ 33 for(int i=0;i<100;i++){ 34  dec(); 35  } 36  } 37 } 38 }