多线程问题-一个输出数字,一个输出字母,交替输出1A2B3C4D...26Z

最近在学习多线程时见到了一道题目,需要我们用两个线程,一个输出字母,一个输出数字,要求输出结果为1A2B3C4D...26Z

多线程问题-一个输出数字,一个输出字母,交替输出1A2B3C4D...26Z_第1张图片

在学习一些视频和资料后,总结了几种比较简洁便于理解的方法:

1.使用LockSupport类中的park和unpark方法,park为阻塞当前线程,unpark(Thread thread)为唤醒传入参数所对应线程。该类属于java.util.concurrent.locks包。下面是代码:

 static Thread t1 = null, t2 = null;

    public static void main(String[] args) {
        String[] aInt = {"1","2","3","4","5","6","7","8","9","10"};
        char[] aChar = {'A','B','C','D','E','F','G','H','I','J'};

        t1 = new Thread(()->{
            for(String c:aInt){
                System.out.print(c);
                LockSupport.unpark(t2);//唤醒进程t2
                LockSupport.park();//阻塞自身进程
            }
        },"t1");

        t2 = new Thread(()->{
            for(char c:aChar){
                LockSupport.park();
                System.out.print(c);
                LockSupport.unpark(t1);
            }
        },"t2");

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

2.while自旋锁

    

enum ReadyToRun {T1,T2};

    static volatile ReadyToRun r = ReadyToRun.T1;

    public static void main(String[] args) {
        String[] aInt = {"1","2","3","4","5","6","7","8","9","10"};
        char[] aChar = {'A','B','C','D','E','F','G','H','I','J'};

        new Thread(()->{
            for(String c:aInt){
                while (r!=ReadyToRun.T1){};//若r不为T1,自旋空转
                System.out.print(c);
                r = ReadyToRun.T2;
            }
        },"t1").start();

        new Thread(()->{
            for(char c:aChar){
                while (r!=ReadyToRun.T2){};//若r不为T2,自旋空转
                System.out.print(c);
                r = ReadyToRun.T1;
            }
        },"t2").start();
    }

3.经典方法   Synchronized加wait,notify操作

这里需要注意的问题是for循环结束之后必须再写一个o.notify(),如果没有调用这个方法,虽然最后的输出结果可能仍然正确,但最后总有一个线程阻塞在wait()操作而无法结束。即出现下面这种情况,输出完成但程序无法结束。

多线程问题-一个输出数字,一个输出字母,交替输出1A2B3C4D...26Z_第2张图片

 public static void main(String[] args) {
        final Object o = new Object();

        String[] aInt = {"1","2","3","4","5","6","7","8","9","10"};
        char[] aChar = {'A','B','C','D','E','F','G','H','I','J'};

        new Thread(()->{
            synchronized (o){
                for(String c:aInt){
                    System.out.print(c);
                    try {
                        o.notify();//叫醒t2
                        o.wait();//阻塞自己
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                o.notify();
            }
        },"t1").start();

        new Thread(()->{
            synchronized (o){
                for(char c:aChar){
                    System.out.print(c);
                    try {
                        o.notify();//叫醒t1
                        o.wait();//阻塞自己
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                o.notify();
            }
        },"t2").start();
    }

 

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