设计4个线程，其中两个线程每次对j增加1，另外两个线程对j每次减少

public class ThreadTest1{   private int j;    public static void main(String args[]){ ThreadTest1 tt=new ThreadTest1(); Inc inc=tt.new Inc(); Dec dec=tt.new Dec(); for(int i=0;i<2;i++){    Thread t=new Thread(inc);   t.start();    t=new Thread(dec);   t.start(); } }    private synchronized void inc(){ j++;  System.out.println(Thread.currentThread().getName()+"-inc:"+j);   }    private synchronized void dec(){ j--;  System.out.println(Thread.currentThread().getName()+"-dec:"+j);   }    class Inc implements Runnable{ public void run(){  for(int i=0;i<100;i++){ inc(); } }   }    class Dec implements Runnable{ public void run(){  for(int i=0;i<100;i++){ dec(); }  }   } }

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