java - 使用两个线程时如何在每次更改后打印值

Question

我有 A 类，我需要它来获取当前日期并修改它。

public class A {

    private Calendar cal = Calendar.getInstance();

    public void change() {
        try
        {
            cal.add(Calendar.MONTH, 1);
            Thread.sleep(1000);
        }
        catch (Exception e)
        {
            System.out.println("Thread  interrupted.");

        }


    }
    public void print() {
       DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");

       System.out.println("Current Date Time : " + dateFormat.format(cal.getTime()));
    }
}

在我的主函数中，我创建了类 A 的实例，并创建了两个线程:一个负责更改日期，另一个负责将其打印到控制台(使用 A 的打印和更改方法)

我想要它做的是在每次更改后打印新日期，但是我打印了相同的日期。

public class Main {

    public static void main(String[] args) throws InterruptedException {
        A a = new A();
        Thread B = new Thread(new Runnable(){
            public void run() {
                for (int i = 0; i < 10; i++) {
                    a.print();
                }
            }

        });

        Thread C = new Thread(new Runnable(){
            public void run(){
                for(int i =0; i<10; i++) {
                    a.change();
                }

            }
        });
        synchronized (a) {
                B.start();
                C.start();

        }
    }
}

输出如下:

Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27
Current Date Time : 2019/12/29 18:27:27

Answer 1

这是您的代码的更新版本，它将适合您:

class A {

private BlockingQueue<Calendar> calList = new ArrayBlockingQueue<Calendar>(1);

public void change() {
    try {
        Calendar cal=Calendar.getInstance();
        while(true) {
            cal.add(Calendar.MONTH, 1);
            calList.add(cal);
            System.out.println("Adding month to date");
            Thread.sleep(1000);
        }
    } catch (Exception e) {
        System.out.println("Thread  interrupted.");

    }

}

public void print() throws InterruptedException {
    while(true) {
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        System.out.println("Current Date Time : " + dateFormat.format(calList.take().getTime()));
    }
}}

目前，它继续循环并添加月份。您可以根据需要更改它:

public static void main(String[] args) throws InterruptedException {
    A a = new A();
    Thread B = new Thread(new Runnable() {
        public void run() {
            try {
                a.print();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    });

    Thread C = new Thread(new Runnable() {
        public void run() {
            a.change();
        }
    });
    B.start();
    C.start();

}