Java多线程练习题

1. 两个线程交替打印1212121212

这题使用了原子的一个状态类表示当前可执行的线程。

/**
 * @Author: tjc
 * @description
 * @Date Created in 14:35 2021-03-03
 * 两个线程交替打印1212121212
 */
public class Demo6 {

    public static void main(String[] args) {
        AtomicInteger i = new AtomicInteger(0);
        new Thread(new Print1(i)).start();
        new Thread(new Print2(i)).start();

    }

}

class Print1 implements Runnable{
    private AtomicInteger i;

    public Print1(AtomicInteger i) {
        this.i = i;
    }

    public void run() {
        while(true) {
            if(i.get() == 0) {
                System.out.print("1");
                i.compareAndSet(0, 1);
            }
        }
    }
}

class Print2 implements Runnable{
    private AtomicInteger i;

    public Print2(AtomicInteger i) {
        this.i = i;
    }


    public void run() {
        while(true) {
            if(i.get() == 1) {
                System.out.print("2");
                i.compareAndSet(1, 0);
            }
        }
    }
}

2. 通过 N 个线程顺序循环打印从 0 至 100

/**
 * @Author: tjc
 * @description
 * @Date Created in 16:05 2021-03-03
 * 通过 N 个线程顺序循环打印从 0 至 100
 */
public class Demo3 {

    public static void main(String[] args) {
        AtomicInteger curThread = new AtomicInteger(1);
        AtomicInteger count = new AtomicInteger(0);
        new Thread(new PrintTask(1, 5, curThread, count)).start();
        new Thread(new PrintTask(2, 5, curThread, count)).start();
        new Thread(new PrintTask(3, 5, curThread, count)).start();
        new Thread(new PrintTask(4, 5, curThread, count)).start();
        new Thread(new PrintTask(5, 5, curThread, count)).start();
    }
}

class PrintTask implements Runnable {

    private AtomicInteger count;
    private int no;
    private int maxNum;
    private AtomicInteger curThread;

    private boolean start = true;

    public PrintTask(int no, int maxNum, AtomicInteger curThread, AtomicInteger count) {
        this.no = no;
        this.maxNum = maxNum;
        this.count = count;
        this.curThread = curThread;
    }

    public void turn() {
        if (curThread.get() >= maxNum) {
            curThread.set(1);
        } else {
            curThread.incrementAndGet();
        }
    }
    
    public void run() {
        while (start) {
            synchronized (curThread) {
                while (no != curThread.get()) {
                    try {
                        curThread.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                turn();
                if (count.get() > 100) {
                    start = false;
                    curThread.notifyAll();
                    break;
                }
                System.out.println("thread" + no + ": " + count.get());
                count.getAndIncrement();
                curThread.notifyAll();
            }
        }
        System.out.println("thread" + no + " end.");
    }
}