java - 为什么操作监听器会阻止我的程序连续递增/递减数字？

Question

我正在尝试编写一个简单的计数器程序，该程序创建一个带有递增/递减按钮的窗口，用于对数字加/减一。我的问题是该程序只能在单击一次后才能运行。我试图让它在多次点击后继续运行。为什么 Action 监听器会阻止多次点击？

示例:

用户类型 5. 单击“+”按钮。结果显示6。
如果用户再次点击，什么也不会发生。

所需功能:

用户类型 5. 单击“+”按钮 5 次。结果应显示 10。

import javax.swing.JFrame;
import java.util.Scanner;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.*;
import java.awt.event.*;
import java.awt.event.KeyEvent;
import java.net.URL;
import javax.swing.AbstractButton;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.lang.*;

public class CounterTestDemo4 extends JFrame
{
// Create Buttons and fields
private JButton jbtAdd = new JButton("+");
private JButton jbtSub = new JButton("-");
private JTextField jtfNumber1 = new JTextField(8);
private JTextField jtfResponse = new JTextField(8);

public static void main(String[] args) 
{

    JFrame frame = new CounterTestDemo4();
    frame.setTitle("Counter Test");
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
 }


public CounterTestDemo4() 
{
    //Create Panel
    JPanel panel = new JPanel();
    panel.add(new JLabel("Enter Number:"));
    panel.add(jtfNumber1);
    panel.add(new JLabel("Result:"));
    panel.add(jtfResponse);
    panel.add(jbtAdd);
    panel.add(jbtSub);
    add(panel);
    BtnListener listener = new BtnListener();
    jbtAdd.addActionListener(listener);
    jbtSub.addActionListener(listener);
}

class JtfListener implements ActionListener {

    @Override
    public void actionPerformed(ActionEvent e) {
     int x = Integer.parseInt(jtfNumber1.getText());
    }
}

 class BtnListener implements ActionListener 
{
    @Override
 public void actionPerformed(ActionEvent e)
  {
 int int1 = Integer.parseInt(jtfNumber1.getText());
 if(e.getSource().equals(jbtAdd))
  {
    int1++;
  jtfResponse.setText(String.valueOf(int1));
  }

 else if( e.getSource().equals(jbtSub) )
 {
    int1--;
    jtfResponse.setText(String.valueOf(int1));
//end if
}//end else if statement
}//end action performed
}//end BtnListner     
}//end CounterTestDemo4

Answer 1

您从一个 JTextField 获取数字并更改另一个 JTextField，但您永远不会获得更改后的数字。建议:不要从 ActionListener 中的任何 JTextField 获取数字。相反，创建一个 int 变量并将数字存储在该变量中。使用文本字段仅用于显示。唯一的异常(exception)是我想如果您想从 JTextField 设置数字，然后在该监听器内部设置 int 字段，但之后使用 int 字段。

然后摆脱 jtfResponse:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class CounterTestDemo4 extends JFrame {
   private JButton jbtAdd = new JButton("+");
   private JButton jbtSub = new JButton("-");
   private JTextField jtfNumber1 = new JTextField(8);

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            JFrame frame = new CounterTestDemo4();
            frame.setTitle("Counter Test");
            frame.setLocationRelativeTo(null);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.pack();
            frame.setVisible(true);
         }
      });

   }

   public CounterTestDemo4() {
      JPanel panel = new JPanel();
      panel.add(new JLabel("Enter Number:"));
      panel.add(jtfNumber1);
      panel.add(new JLabel("Result:"));
      panel.add(jbtAdd);
      panel.add(jbtSub);
      add(panel);
      BtnListener listener = new BtnListener();
      jbtAdd.addActionListener(listener);
      jbtSub.addActionListener(listener);
   }

   class BtnListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent e) {
         int int1;
         try {
            int1 = Integer.parseInt(jtfNumber1.getText());
            if (e.getSource().equals(jbtAdd)) {
               int1++;
               jtfNumber1.setText(String.valueOf(int1));
            }

            else if (e.getSource().equals(jbtSub)) {
               int1--;
               jtfNumber1.setText(String.valueOf(int1));
            }
         } catch (NumberFormatException e1) {
            JOptionPane.showMessageDialog(jtfNumber1,
                  "Please enter a number in the text field",
                  "Text Field Without Number", JOptionPane.ERROR_MESSAGE);
            jtfNumber1.selectAll();
            jtfNumber1.requestFocusInWindow();
         }
      }
   }
}