设计 4 个线程，其中两个线程每次对 j 增加 1

public class ThreadTest{

	private int j;

	class Inc implements Runnable{
		@Override
		public void run() {
			// TODO Auto-generated method stub
			for(int i=0;i<100;i++) {
				inc();
			}
		}
	}

	//	相加操作
	private synchronized void inc() {
		// TODO Auto-generated method stub
		j++;
		System.out.println(Thread.currentThread().getName() + "-inc:"+j);
	}

	class Dec implements Runnable{
		@Override
		public void run() {
			// TODO Auto-generated method stub
			for(int i=0;i<100;i++) {
				dec();
			}
		}
	}

	//	相减操作
	private synchronized void dec() {
		// TODO Auto-generated method stub
		j--;
		System.out.println(Thread.currentThread().getName() + "-dec:"+j);
	}

	public static void main(String[] args) {
	
		ThreadTest thread = new ThreadTest();		
		Inc inc = thread.new Inc();
		Dec dec = thread.new Dec();
		for(int i=0;i<2;i++) {
			Thread t = new Thread(inc);
			t.start();
			t = new Thread(dec);
			t.start();
		}
		
	}
	
}