交叉打印 0-100

方法1

關於 notify / notifyAll / wait，可參考：
https://www.cnblogs.com/moongeek/p/7631447.html

public class Solution {
    public static void main(String[] args) {
        Solution s = new Solution();
        Runnable r = () -> s.jiaocha();
        new Thread(r).start();
        new Thread(r).start();
        Thread.sleep(100000);
    }

    volatile int i = 0;
    private void jiaocha() {
        // notify / wait 必須同 synchronized 一起使用，且都是基於同一個對象，本例中爲 this
        synchronized (this) {
            while (i <= 100) {
                // 後啓動的線程喚醒先啓動的線程
                // 先啓動的線程打印第一條數據
                this.notify();
                this.mywait();
                System.out.println(Thread.currentThread().getName() + ":  " + i);
                i++;
            }
        }
    }

    private void mywait() {
        try {
            this.wait();
        } catch (Throwable e) {
        }
    }
}

方法2

    volatile boolean flag = false;

    private void jiaocha() {
        Runnable r1 = () -> {
            for (int i = 0; i <= 100; i += 2) {
                while (flag) {
                    continue;
                }
                System.out.println(Thread.currentThread().getName() + ":  " + i);
                flag = true;
            }
        };

        Runnable r2 = () -> {
            for (int i = 1; i <= 100; i += 2) {
                while (!flag) {
                    continue;
                }
                System.out.println(Thread.currentThread().getName() + ":  " + i);
                flag = false;
            }
        };

        new Thread(r1).start();
        new Thread(r2).start();
    }