设计4个线程，两个对i加1，两个对j减1

public class fourThread {

	int i = 10;
	int j = 50;

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		 fourThread ft = new fourThread();
		plus addi = ft.new plus();
		minus minusj = ft.new minus();
		Thread t = new Thread(addi);
		t.start();
		Thread t1 = new Thread(addi);
		t1.start();
		Thread tj = new Thread(minusj);
		tj.start();
		Thread tj1 = new Thread(minusj);
		tj1.start();
	}

	public synchronized void add() {
		i++;
		System.out.println(Thread.currentThread().getName()
				+ "对i + 1 : " + i);
	}
	public synchronized void minus() {
		j--;
		System.out.println(Thread.currentThread().getName()
				+ "对j - 1 : " + j);
	}

	class plus implements Runnable {

		@Override
		public void run() {
			// TODO Auto-generated method stub
			for (int q = 0; q < 10; q++) {
				add();
			}
		}

	}

	class minus implements Runnable {

		@Override
		public void run() {
			// TODO Auto-generated method stub
			for (int p = 0; p < 10; p++) {
				minus();
			}
		}
	}
}

运行结果：

Thread-0对i + 1 : 11
Thread-3对j - 1 : 49
Thread-3对j - 1 : 48
Thread-3对j - 1 : 47
Thread-3对j - 1 : 46
Thread-3对j - 1 : 45
Thread-3对j - 1 : 44
Thread-3对j - 1 : 43
Thread-3对j - 1 : 42
Thread-3对j - 1 : 41
Thread-3对j - 1 : 40
Thread-0对i + 1 : 12
Thread-0对i + 1 : 13
Thread-0对i + 1 : 14
Thread-0对i + 1 : 15
Thread-0对i + 1 : 16
Thread-0对i + 1 : 17
Thread-0对i + 1 : 18
Thread-0对i + 1 : 19
Thread-0对i + 1 : 20
Thread-2对j - 1 : 39
Thread-2对j - 1 : 38
Thread-2对j - 1 : 37
Thread-2对j - 1 : 36
Thread-2对j - 1 : 35
Thread-2对j - 1 : 34
Thread-2对j - 1 : 33
Thread-2对j - 1 : 32
Thread-2对j - 1 : 31
Thread-2对j - 1 : 30
Thread-1对i + 1 : 21
Thread-1对i + 1 : 22
Thread-1对i + 1 : 23
Thread-1对i + 1 : 24
Thread-1对i + 1 : 25
Thread-1对i + 1 : 26
Thread-1对i + 1 : 27
Thread-1对i + 1 : 28
Thread-1对i + 1 : 29
Thread-1对i + 1 : 30