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。

package cn.thread.test;

/*
 * 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。
 */
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();
		
		
		Thread t1 = new Thread(inc);
		Thread t2 = new Thread(dec);
		Thread t3 = new Thread(inc);
		Thread t4 = new Thread(dec);
		t1.start();
		t2.start();
		t3.start();
		t4.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 {
		@Override
		public void run() {
			for (int i = 0; i < 100; i++) {
				inc();
			}
		}
	}
	
	class Dec extends Thread {
		@Override
		public void run() {
			for (int i = 0; i < 100; i++) {
				dec();
			}
		}
	}
}