两个线程交替打印 0 - 99

volatile 控制

public class ThreadPrint {

    private static volatile int i = 0;
    private static volatile boolean who = true;

    public static void main(String[] args) {
        new Thread(() -> {
            while (true) {
                if (who) {
                    // 出口
                    if (i == 100) {
                        who = !who;
                        break;
                    }
                    System.out.println("t1 = " + i);
                    i++;
                    who = !who;
                }
            }
        }).start();

        new Thread(() -> {
            while (true) {
                if (!who) {
                    if (i == 100) {
                        who = true;
                        break;
                    }
                    System.out.println("t2 - " + i);
                    i++;
                    who = !who;
                }
            }
        }).start();
    }

}

notify 机制

public class ThreadPrint {

    private static volatile int i = 0;
    private static Object lock = new Object();

    public static void main(String[] args) {
        new Thread(() -> {
            synchronized(lock) {
                while (true) {
                    if (i == 100) break;
                    System.out.println("t1 - " + i);
                    i++;
                    lock.notify();
                    try {
                        // 释放锁
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                // 通知另一线程结束
                lock.notify();
            }
        }).start();

        new Thread(() -> {
            synchronized (lock) {
                while (true) {
                    if (i == 100) break;
                    System.out.println("t2 - " + i);
                    i++;
                    lock.notify();
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                // 通知另一线程结束
                lock.notify();
            }
        }).start();
    }

}