不讲武德(手动狗头)：面试官上来就甩给我几道多线程代码题叫我手撕，我心里拔凉拔凉的~~~

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前言

栗花落香奈乎

女主真好看

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两个线程，一个线程打印奇数，一个线程打印偶数

ReentrantLock + Condition 来实现

public class Main {


    private static Lock lock = new ReentrantLock();
    static Condition c1 = lock.newCondition();
    static Condition c2 = lock.newCondition();

	//数字
    static volatile int num = 1;

    public static void main(String[] args) {


		//线程A
        new Thread(() -> {
            lock.lock();
            try{
                while (true) {
                	//如果是奇数
                    if (num % 2 == 1) {
                        System.out.println(Thread.currentThread().getName() + "打印奇数：\t" + num);
                        num++;
                        c2.signal();
                        c1.await();
                    }
                }
            }catch(Exception e){
                e.printStackTrace();
            }finally{
                lock.unlock();
            }
        },"A").start();

		//线程B
        new Thread(() -> {
            lock.lock();
            try{
                while (true) {
                	//如果是偶数
                    if (num % 2 == 0) {
                        System.out.println(Thread.currentThread().getName() + "打印偶数：\t" + num);
                        num++;
                        TimeUnit.SECONDS.sleep(1);
                        c1.signal();
                        c2.await();
                    }
                }
            }catch(Exception e){
                e.printStackTrace();
            }finally{
                lock.unlock();
            }
        },"B").start();

    }


}

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三个线程打印ABC

public class Main {

    private static int state = 0;
    private static final Lock lock = new ReentrantLock();

    public static void main(String[] args) {

        //打印A
        Thread a = new Thread(() -> {
            while (true) {
                lock.lock();
                try{
                    if (state % 3 == 0) {
                        System.out.print("A");
                        state++;
                    }
                }catch(Exception e){
                    e.printStackTrace();
                }finally{
                    lock.unlock();
                }
            }
        });

        //打印B
        Thread b = new Thread(() -> {
            while (true) {
                lock.lock();
                try{
                    if (state % 3 == 1) {
                        System.out.print("B");
                        state++;
                    }
                }catch(Exception e){
                    e.printStackTrace();
                }finally{
                    lock.unlock();
                }
            }
        });

        //打印C
        Thread c  = new Thread(() -> {
            while (true) {
                lock.lock();
                try{
                    if (state % 3 == 2) {
                        System.out.println("C");
                        TimeUnit.SECONDS.sleep(1);
                        state++;
                    }
                }catch(Exception e){
                    e.printStackTrace();
                }finally{
                    lock.unlock();
                }
            }
        });

        a.start();
        b.start();
        c.start();
    }

}

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线程打印A5次，B10次，C15次

public class Test01 {


    private int number = 1;
    private static Lock lock = new ReentrantLock();
    static Condition c1 = lock.newCondition();
    static Condition c2 = lock.newCondition();
    static Condition c3 = lock.newCondition();


    public void printNum(int num,Condition st,Condition start,int currentNum,int futureNum) {
        lock.lock();
        try{
            while (number != currentNum) {
                st.await();
            }
            for (int i = 1; i <= num; i++) {
                System.out.println(Thread.currentThread().getName() + "\t" + i);
            }
            number = futureNum;
            start.signal();
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            lock.unlock();
        }

    }


    public static void main(String[] args) {
        Test01 test01 = new Test01();

        new Thread(() -> {
            for (int i = 0; i < 2; i++) {
                test01.printNum(5,c1,c2,1,2);
            }
        },"AAA").start();

        new Thread(() -> {
            for (int i = 0; i < 2; i++) {
                test01.printNum(10,c2,c3,2,3);
            }
        },"BBB").start();

        new Thread(() -> {
            for (int i = 0; i < 2; i++) {
                test01.printNum(15,c3,c1,3,1);
            }
        },"CCC").start();
    }
}

图没截完

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创建水分子

实现两个方法生成一个水分子H2O，一个方法输出一个O,另一个方法输出一个H,水分子需要由2个H和一个O构成，

public class Main {


    private static ReentrantLock lock = new ReentrantLock();
    private static Condition c1 = lock.newCondition();
    private static Condition c2 = lock.newCondition();
    private static AtomicInteger num = new AtomicInteger(1);

    public static void printH2() {
        lock.lock();
        try{
            System.out.print("H");
            if (num.intValue() % 2 == 0) {
                c2.signal();
                c1.await();
            }else {
                num.incrementAndGet();
                printH2();
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            lock.unlock();
        }
    }

    public static void printO() {
        lock.lock();
        try{
            System.out.println("O");
            TimeUnit.SECONDS.sleep(1);
            num.incrementAndGet();
            c1.signal();
            c2.await();
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            lock.unlock();
        }
    }

    public static void main(String[] args) {

        new Thread(() -> {
            while (true) {
                printH2();
            }
        },"1").start();

        new Thread(() -> {
            while (true) {
                printO();
            }
        },"2").start();
    }



}

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生产者、消费者阻塞普通版

public class Test01 {


    private Lock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();
    private volatile int num = 0;

    //生产者
    public void produce() {
        lock.lock();
        try{
            //如果不等于0，那么就不去生产
            while (num != 0) {
                condition.await();
            }
            //生产
            num++;
            System.out.println(Thread.currentThread().getName() + "\t生产：" + num);
            //唤醒
            condition.signal();
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            lock.unlock();
        }
    }


    //消费者
    public void consumer() {
        lock.lock();
        try{
            //如果恒等于0，那么就不能去消费
            while (num == 0) {
                condition.await();
            }
            //消费
            num--;
            System.out.println(Thread.currentThread().getName() + "\t消费：" + num);
            TimeUnit.SECONDS.sleep(1);
            //唤醒
            condition.signal();
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            lock.unlock();
        }
    }

    public static void main(String[] args) {

        Test01 test = new Test01();

        new Thread(() -> {
            while (true) {
                test.produce();
            }
        },"A").start();

        new Thread(() -> {
            while (true) {
                test.consumer();
            }
        },"B").start();
    }
}

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生产者、消费者阻塞队列版

public class Test01 {


    public static void main(String[] args) {
        //将阻塞队列容量初始化为5
        MySource source = new MySource(new ArrayBlockingQueue<>(5));

        new Thread(() -> {
            System.out.println(Thread.currentThread().getName() + "\t 生产线程启动");
            try {
                source.myProduct();
            }catch (Exception e) {
                e.printStackTrace();
            }
        },"Product").start();

        new Thread(() -> {
            System.out.println(Thread.currentThread().getName() + "\t 消费线程启动");
            System.out.println();
            try {
                source.myConsumer();
            }catch (Exception e) {
                e.printStackTrace();
            }
        },"Consumer").start();


		//5秒后退出
        try {
            TimeUnit.SECONDS.sleep(5);
        }catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println();
        System.out.println("时间到，结束！");
        source.stop();
    }
}


class MySource {
    private volatile boolean FLAG = true; // 默认开启 生产+消费

    private AtomicInteger atomicInteger = new AtomicInteger();

    //阻塞队列
    BlockingQueue<String> blockingQueue = null;

    public MySource(BlockingQueue<String> blockingQueue) {
        this.blockingQueue = blockingQueue;
    }


    //生产者
    public void myProduct() throws Exception {
        String data = null;
        boolean retValue;
        while (FLAG) {
            data = atomicInteger.incrementAndGet() + "";
            //添加到阻塞队列，默认过期时间为2秒，offer方法返回的是 boolean值
            retValue = blockingQueue.offer(data,2L, TimeUnit.SECONDS);
            if (retValue) {
                System.out.println(Thread.currentThread().getName() + "\t 插入队列成功" + data);
            }else {
                System.out.println(Thread.currentThread().getName() + "\t 插入队列失败" + data);
            }
            TimeUnit.SECONDS.sleep(1);
        }
        System.out.println(Thread.currentThread().getName() + "\t 停止生产");
    }

    //消费者
    public void myConsumer() throws Exception {
        String result = null;
        while (FLAG) {
            //两秒钟从队列中取不到就不放弃不取了
            result = blockingQueue.poll(2L,TimeUnit.SECONDS);
            //如果从队列中拿不到值，或者为 ""，
            if (null == result || "".equals(result)) {
                FLAG = false;
                System.out.println(Thread.currentThread().getName() + "\t 超时，消费退出");
                return;
            }

            System.out.println(Thread.currentThread().getName() + "\t 消费队列成功" + result);
        }
        System.out.println(Thread.currentThread().getName() + "\t 停止消费");
    }

    public void stop() {
        this.FLAG = false;
    }
}

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最后

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