面试题101

8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1。写出程序。

以下程序使用内部类实现线程，对j增减的时候没有考虑顺序问题。

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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