用线程交替打印奇偶数

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;


public class TwoThread {

    private int start = 1;

    /**
     * 对 flag 的写入虽然加锁保证了线程安全，但读取的时候由于 不是 volatile 所以可能会读取到旧值
     *
     */
    private volatile boolean flag = false;

    /**
     * 重入锁
     */
    private final static Lock LOCK = new ReentrantLock();

    public static void main(String[] args) {
        TwoThread twoThread = new TwoThread();

        Thread t1 = new Thread(new OuNum(twoThread));
        t1.setName("t1");


        Thread t2 = new Thread(new JiNum(twoThread));
        t2.setName("t2");

        t1.start();
        t2.start();
    }

    /**
     * 偶数线程
     */
    public static class OuNum implements Runnable {

        private TwoThread number;

        public OuNum(TwoThread number) {
            this.number = number;
        }

        @Override
        public void run() {
            while (number.start <= 1000) {

                if (number.flag) {
                    try {
                        LOCK.lock();
                        System.out.println(Thread.currentThread().getName() + "+-+" + number.start);
                        number.start++;
                        number.flag = false;


                    } finally {
                        LOCK.unlock();
                    }
                }
            }
        }
    }

    /**
     * 奇数线程
     */
    public static class JiNum implements Runnable {

        private TwoThread number;

        public JiNum(TwoThread number) {
            this.number = number;
        }

        @Override
        public void run() {
            while (number.start <= 1000) {

                if (!number.flag) {
                    try {
                        LOCK.lock();
                        System.out.println(Thread.currentThread().getName() + "+-+" + number.start);
                        number.start++;
                        number.flag = true;


                    } finally {
                        LOCK.unlock();
                    }
                }
            }
        }
    }
}