不太好的方法：用synchronized實(shí)現(xiàn)

當(dāng)其中一個(gè)線程一直持有鎖時(shí)，會(huì)重復(fù)執(zhí)行 if 判斷，做無(wú)用功！

/**
 * 兩個(gè)線程交替打印0-100的奇偶數(shù)，
 * 用synchronized關(guān)鍵字實(shí)現(xiàn)
 */
public class WaitNotifyPrintOddEvenSyn {

    // 新建2個(gè)線程
    // 1個(gè)只處理偶數(shù)，第二個(gè)只處理奇數(shù)（用位運(yùn)算）
    // 用synchronized來(lái)通信

    private static int count;

    private static final Object lock = new Object();

    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (count < 100) {
                    synchronized (lock) {
                        if ((count & 1) == 0) {
                            System.out.println(Thread.currentThread().getName() + ":" + count++);
                        }
                    }
                }
            }
        }, "偶數(shù)線程").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (count < 100) {
                    synchronized (lock) {
                        if ((count & 1) == 1) {
                            System.out.println(Thread.currentThread().getName() + ":" + count++);
                        }
                    }
                }
            }
        }, "奇數(shù)線程").start();
    }
}

更好的實(shí)現(xiàn)方法：用wait和notify實(shí)現(xiàn)

/**
 * 兩個(gè)線程交替打印0-100的奇偶數(shù)，
 * 用wait和notify實(shí)現(xiàn)
 */
public class WaitNotifyPrintOddEvenWait {

    // 1.拿到鎖，就打印
    // 2.打印完，喚醒其它線程，自己休眠

    private static int count = 0;

    private static final Object lock = new Object();

    static class TurningRunner implements Runnable {

        @Override
        public void run() {
            while (count <= 100) {
                synchronized (lock) {
                    System.out.println(Thread.currentThread().getName() + ":" + count++);
                    lock.notify();
                    if (count <= 100) {
                        try {
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    }

    public static void main(String[] args) {
        new Thread(new TurningRunner(), "偶數(shù)線程").start();
        new Thread(new TurningRunner(), "奇數(shù)線程").start();
    }
}