如何将秒表制作为Java中的线程？

Question

我正在尝试实现一个类似于Is there a stopwatch in Java? 的秒表，但作为Thread。

我的SecondsCounter 类实现了Runnable，然后调用它的start 方法将创建一个线程作为局部变量。

似乎该线程与run 方法中的第一行冲突：this.runningTime = System.currentTimeMillis(); ...因为条件while (this.runningTime < this.endTime) 从不 损坏（无限循环）...

那么让一个类既实现Runnable 并且包含它的Thread 也是不正确的吗？

---

这是具有主要方法的类：

public class MultithreadingTest {

    public static void main(String[] args) {
        int totalSeconds = 5;
        SecondsPrinter printer = new SecondsPrinter(totalSeconds);
        printer.startPrinting();
    }
} // end of class

...秒打印机类：

public class SecondsPrinter {

    // composition here:
    private SecondsCounter clock;

    public SecondsPrinter(int totalSeconds) {
        this.clock = new SecondsCounter(totalSeconds);
    }

    public void startPrinting() {
        this.clock.start();
        while (this.clock.isRunning()) {

            // this is incorrectly always printing the maximum seconds value:
            System.out.println(this.clock.getCurrentSecond());
        }
    }
} // end of class

...和秒计数器类：

public class SecondsCounter implements Runnable {

    private int totalSeconds, currentSecond;
    private long startTime, runningTime, endTime;
    private Thread thread;

    public SecondsCounter(int totalSeconds) {
        this.totalSeconds = totalSeconds;
    }

    public int getCurrentSecond() {
        return this.currentSecond;
    }

    @Override
    public void run() {
        this.runningTime = System.currentTimeMillis();

        // this is an infinite loop, but it shouldn't be:
        while (this.runningTime < this.endTime) {
            this.currentSecond = (int)(this.endTime - this.runningTime) / 1000;
        }

        // this code is never reached:
        this.stop();
    }

    public void start() {
        this.startTime = System.currentTimeMillis();
        this.runningTime = this.startTime;
        this.endTime = this.startTime + (this.totalSeconds * 1000);

        // multithreading here:
        this.thread = new Thread(this);
        this.thread.start();
    }

    public boolean isRunning() {
        return this.thread.isAlive();
    }

    public void stop() {
        this.thread.interrupt();
        this.thread = null;
    }
} // end of class

Answer 1

其实这应该是一个无限循环。看看你的循环。

while (this.runningTime < this.endTime) {
    this.currentSecond = (int)(this.endTime - this.runningTime) / 1000;
}

条件表明它将在runningTime < endTime 时循环。 runningTime 在哪里更新？如果你在循环中添加这样的东西，它应该可以工作：

public void run() {
    this.runningTime = System.currentTimeMillis();

    // no longer an infinite loop
    while (this.runningTime < this.endTime) {
        this.currentSecond = (int)(this.endTime - this.runningTime) / 1000;
        this.runningTime = System.currentTimeMillis();
    }

    // this code is now reached.
    this.stop();
}

您甚至可以组合它（或完全删除变量 runningTime）：

public void run() {
    while ((this.runningTime = System.currentTimeMillis()) < this.endTime) {
        this.currentSecond = (int)(this.endTime - this.runningTime) / 1000;
    }

    this.stop();
}