Java多线程轮流打印ABC的四种实现方式

ABCABCABCABCABC

/*
 1.设置共享变量state控制线程的执行顺序
 2.在打印方法中传入两个参数：打印的内容， 当前线程的state
 3.每个线程在调用打印方法时都要传入自己对应的顺序，A：0，B：1，C：2
*/
public class PrintABC {
    private static int state = 0;// 设置共享变量控制线程执行顺序
    private static final int COUNT = 5;// 控制执行顺序
    private static Object lock = new Object();// 用于加锁的对象

    public static void main(String[] args) {
        Thread t1 = new Thread(() -> {
            try {
                printChar("A", 0);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        });
        Thread t2 = new Thread(() -> {
            try {
                printChar("B", 1);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        });
        Thread t3 = new Thread(() -> {
            try {
                printChar("C", 2);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        });

        t1.start();
        t2.start();
        t3.start();
    }

    private static void printChar(String name, int curState) throws InterruptedException {
        int i = 0;
        while(i < COUNT) {
            synchronized (lock) {
                if(state % 3 == curState) {// 是当前线程的执行顺序
                    System.out.print(name + " ");
                    i++;// 控制当前线程的执行的次数
                    state++;// 轮转到下一个线程
                    lock.notifyAll();
                }else {// 轮不到当前线程  wait等待
                    lock.wait();
                }
            }
        }
    }
}

    /*
     *第四种方法：ReentrantLock + Condition 来实现更加精确的线程间通信
     * ReentrantLock实现加锁，解锁； Condition实现线程间的通信
     */

    public static final int COUNT = 5;
    public static int state = 0;
    public static ReentrantLock lock = new ReentrantLock();
    public static Condition conA = lock.newCondition();
    public static Condition conB = lock.newCondition();
    public static Condition conC = lock.newCondition();

    public static void main(String[] args) {
        new Thread(() ->printChar("A", 0, conA, conB)).start();
        new Thread(() ->printChar("B", 1, conB, conC)).start();
        new Thread(() ->printChar("C", 2, conC, conA)).start();
    }

    private static void printChar(String name, int curState, Condition curCondition, Condition nextCondition) {
        for(int i = 0; i < COUNT; i++) {
            lock.lock();
                try {
                    while(state % 3 != curState)
                        curCondition.await();

                    // 是当前线程  执行
                    System.out.print(name);
                    state++;
                    nextCondition.signal();

                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }finally {
                    lock.unlock();
                }

        }
    }

    /*
     * 第二种方法：使用Semaphore 信号量的方式控制执行顺序
     * 如何保证先打印A：semA, semB, semC  将A的许可设置为1，B,C的许可设置为0，则一定先执行A
     * 如何保证打印顺序：在打印方法中传入三个参数：name， curSem, nextSem  A-B  B-C  C-A
     * 执行完当前线程打印内容之后，让下一个线程release一个许可
     */

    private static final Semaphore semA = new Semaphore(1);
    private static final Semaphore semB = new Semaphore(0);
    private static final Semaphore semC = new Semaphore(0);
    private static final int COUNT = 5;

    public static void main(String[] args) {
        new Thread(() -> printChar("A", semA, semB)).start();
        new Thread(() -> printChar("B", semB, semC)).start();
        new Thread(() -> printChar("C", semC, semA)).start();
    }

    private static void printChar(String name, Semaphore cur, Semaphore next) {
        for(int i = 0; i < COUNT;) {
            try {
                cur.acquire();
                System.out.print(name + " ");
                ++i;
                next.release();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }

    /*
     * 第三种方法：使用BlockingQueue作为令牌的方式来控制打印顺序
     * 创建三个队列，每个队列分别打印对应需要打印的内容
     * 使用令牌来控制打印的顺序，和使用semaphore类似
     * 在打印的方法中传入三个参数：要打印的内容，当前队列，下一个队列
     */

    public static BlockingQueue<String> qA = new ArrayBlockingQueue<>(1);
    public static BlockingQueue<String> qB = new ArrayBlockingQueue<>(1);
    public static BlockingQueue<String> qC = new ArrayBlockingQueue<>(1);
    public static final int COUNT = 5;

    public static void main(String[] args) throws InterruptedException {
        new Thread(() -> printChar("A", qA, qB)).start();
        new Thread(() -> printChar("B", qB, qC)).start();
        new Thread(() -> printChar("C", qC, qA)).start();

        qA.put("go");
    }

    private static void printChar(String name, BlockingQueue<String> curQueue, BlockingQueue<String> nextQueue) {
        for(int i = 0; i < COUNT; i++) {
            try {
                curQueue.take();// 等待令牌传递
                System.out.print(name + " ");
                nextQueue.put("go");// 传递令牌
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }