求教一个简单的多线程小程序,该如何处理

public class TestThread {    private int j;        public static void main(String[] args) {        TestThread t = new TestThread();        Inc inc = t.new Inc();        Dec dec = t.new Dec();        for(int i=0;i<2;i++){            Thread thread = new Thread(inc);            thread.start();            thread = new Thread(dec);            thread.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);    }    //内部类    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();            }            }    }}