java常见并发面试题目+示例代码

1、现在有线程 T1、T2 和 T3。你如何确保 T2 线程在 T1 之后执行，并且 T3 线程在 T2 之后执行？

这个线程面试题通常在第一轮面试或电话面试时被问到，这道多线程问题为了测试面试者是否熟悉join方法的概念。答案也非常简单——可以用 Thread 类的join方法实现这一效果。

public class Test {

    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread() {
            public void run() {
                System.out.println("1");
            }
        };
        Thread t2 = new Thread() {
            public void run() {
                System.out.println("2");
            }
        };
        Thread t3 = new Thread() {
            public void run() {
                System.out.println("3");
            }
        };
        
        t1.start();
        t1.join();//阻塞住直到t1完成
        t2.start();
        t2.join();
        t3.start();
        System.out.println("end");
    }
}

 

 

 2、两线程奇偶数打印

public class Test {
    static class SoulutionTask implements Runnable {
        static int value = 0;

        @Override
        public void run() {
            while (value <= 100) {
                synchronized (SoulutionTask.class) {
                    System.out.println(Thread.currentThread().getName() + ":" + value++);
                    SoulutionTask.class.notify();
                    try {
                        SoulutionTask.class.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new Thread(new SoulutionTask(), "偶数").start();
        new Thread(new SoulutionTask(), "奇数").start();
    }
}

 

N个线程循环打印

public class Test implements Runnable {
    private static final Object LOCK = new Object();
    /**
     * 当前即将打印的数字
     */
    private static int current = 0;
    /**
     * 当前线程编号，从0开始
     */
    private int threadNo;
    /**
     * 线程数量
     */
    private int threadCount;
    /**
     * 打印的最大数值
     */
    private int maxInt;

    public Test(int threadNo, int threadCount, int maxInt) {
        this.threadNo = threadNo;
        this.threadCount = threadCount;
        this.maxInt = maxInt;
    }

    @Override
    public void run() {
        while (true) {
            synchronized (LOCK) {
                // 判断是否轮到当前线程执行
                while (current % threadCount != threadNo) {
                    if (current > maxInt) {
                        break;
                    }
                    try {
                        // 如果不是，则当前线程进入wait
                        LOCK.wait();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
                // 最大值跳出循环
                if (current > maxInt) {
                    break;
                }
                System.out.println("thread" + threadNo + " : " + current);
                current++;
                // 唤醒其他wait线程
                LOCK.notifyAll();
            }
        }
    }

    public static void main(String[] args) {
        int threadCount = 3;
        int max = 100;
        for (int i = 0; i < threadCount; i++) {
            new Thread(new Test(i, threadCount, max)).start();
        }
    }
}