秒表计划

Question

我有一个针对我的Java I类的秒表程序，它来自Java基础第3版第6.22页，我无法运行它。我不确定我哪里出错了。任何有助于破译该问题的帮助将不胜感激！该程序应该有一个3按钮设置和秒表计数秒，没什么花哨的。我有按钮本身的问题，我不能让他们启动，停止和重置计时器。我正在使用Jgrasp作为我的编译器，所有编译都很好。没有错误报告。我不确定我的if / else语句是否正确，或者我是否留下了一些不让计时器开始计数的东西。下面是作业的内容：设计并实现一个作为秒表的应用程序。包括显示以增量为单位的时间（以秒为单位）的显示。包括允许用户启动和停止时间的按钮，并将显示重置为零。

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class Assignment_6_22_Panel extends JPanel
{
  private JButton start, stop, reset;
  private JLabel label;
  private JPanel buttonPanel;
  private Timer timer; 
  private int time = 0;
  private final int DELAY = 1000;


public Assignment_6_22_Panel()
{
  label = new JLabel("Time: " + time);
  setBackground(Color.white);

  start = new JButton("Start");
  stop = new JButton("Stop");
  reset = new JButton("Reset");

  ButtonListener listener = new ButtonListener();
  TimeListener watchListener = new TimeListener();

  timer = new Timer(DELAY, watchListener);

  start.addActionListener(listener);
  stop.addActionListener(listener);
  reset.addActionListener(listener);



  buttonPanel = new JPanel();
  buttonPanel.setPreferredSize(new Dimension(200, 150));
  buttonPanel.setBackground(Color.white);
  buttonPanel.add(start);
  buttonPanel.add(stop);
  buttonPanel.add(reset);
  add(buttonPanel);
  add(label);

}


private class ButtonListener implements ActionListener
{

  public void actionPerformed(ActionEvent event)
  {
     if (event.getSource() == start)
        timer.start();

     else
         if (event.getSource() == stop)
            timer.stop();
         else
            time = 0;

  }
 }

private class TimeListener implements ActionListener
{

  public void actionPerformed(ActionEvent event)
  {

        label = new JLabel("Your Time: " + time);


  }
 }
}

这是相邻的代码

 import java.awt.*;
 import java.awt.event.*;
 import javax.swing.*;

 public class Assignment_6_22
 {
 //-----------------------------------------------------------------
 //  Displays the main frame of the program.
 //-----------------------------------------------------------------
  public static void main(String[] args)
  {
  JFrame frame = new JFrame("Stop Watch");
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  frame.getContentPane().add(new Assignment_6_22_Panel());

  frame.pack();
  frame.setVisible(true);
  }
 }

Answer 1

您的Timer代码和ButtonListener代码运行正常，问题出在TimerListener ...

private class TimeListener implements ActionListener {

    public void actionPerformed(ActionEvent event) {

        label = new JLabel("Your Time: " + time);

    }
}

每次JLabel触发时，您都会创建Timer的新实例，这与屏幕上显示的内容无关，而是需要设置现有的标签。

此外，您无法在何处实际更新time的值以显示时间的推移......

private class TimeListener implements ActionListener {

    public void actionPerformed(ActionEvent event) {

        time++;
        label.setText("Your Time: " + time);

    }
}

当您reset Timer时，您还应该确保更新label

private class ButtonListener implements ActionListener {

    public void actionPerformed(ActionEvent event) {
        if (event.getSource() == start) {
            timer.start();
        } else if (event.getSource() == stop) {
            timer.stop();
        } else {
            time = 0;
            label.setText("Your Time: " + time);
        }

    }
}