如何在Java秋千中动态更改和相互关联的文本字段

Question

我刚刚开始学习java swings。实际上，我正计划在有3个文本字段，卢比和日元的情况下制作一个货币转换器。当我编辑美元的文本字段时，我希望其他两个文本字段动态更改为适当的转换后的货币值。我一开始尝试使用DocumentListener，但失败了。所以我尝试了addKeylistener。当我更改第一个文本字段时，它可以很好地工作，但是当我首先更改第二或第三个字段时，我会得到不熟悉的泵送事件和线程错误。请在此处查看代码。预先感谢您。

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JButton;
import net.miginfocom.swing.MigLayout;
import javax.swing.JTextField;
import java.awt.GridBagLayout;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.GridBagConstraints;
import javax.swing.JLabel;
public class Conv {
private JFrame frame;
private JTextField textField1;
private JTextField textField2;
private JTextField textField3;
private JLabel lblNum;
private JLabel lblNum_1;
private JLabel lblNum_2;
/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Conv window = new Conv();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}
/**
 * Create the application.
 */
public Conv() {
    initialize();
}
/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(null);
    textField1 = new JTextField();
    textField1.setBounds(170, 69, 86, 20);
    frame.getContentPane().add(textField1);
    textField1.setColumns(10);
    textField2 = new JTextField();
    textField2.setBounds(170, 111, 86, 20);
    frame.getContentPane().add(textField2);
    textField2.setColumns(10);
    textField3 = new JTextField();
    textField3.setBounds(170, 155, 86, 20);
    frame.getContentPane().add(textField3);
    textField3.setColumns(10);
    lblNum = new JLabel("Dollar");
    lblNum.setBounds(114, 72, 46, 14);
    frame.getContentPane().add(lblNum);
    lblNum_1 = new JLabel("Rupees");
    lblNum_1.setBounds(114, 114, 46, 14);
    frame.getContentPane().add(lblNum_1);
    lblNum_2 = new JLabel("Yen");
    lblNum_2.setBounds(114, 158, 46, 14);
    frame.getContentPane().add(lblNum_2);
    textField1.addKeyListener(new KeyAdapter() {
          public void keyReleased(KeyEvent e1) {    
            textField2.setText("");
            textField3.setText("");  
            Double d1,d2,d3;
            d1 = Double.parseDouble(textField1.getText());
            d2 = d1 + 1;
            d3 = d1 + 2;
            textField2.setText(Double.toString(d2));
            textField3.setText(Double.toString(d3));
          }
        });
    textField2.addKeyListener(new KeyAdapter() {
          public void keyTyped(KeyEvent e2) {
              textField1.setText("");
                textField3.setText("");  
                Double d1,d2,d3;
                d2 = Double.parseDouble(textField2.getText());
                d1 = d2 - 1;
                d3 = d2 + 1;
                textField1.setText(Double.toString(d1));
                textField3.setText(Double.toString(d3));
          }
        });
    textField3.addKeyListener(new KeyAdapter() {

          public void keyPressed(KeyEvent e3) {
              textField1.setText("");
                textField2.setText("");  
                Double d1,d2,d3;
                d3 = Double.parseDouble(textField3.getText());
                d1 = d3 - 2;
                d2 = d3 - 1;
                textField1.setText(Double.toString(d1));
                textField2.setText(Double.toString(d2));
          }
        });
      }
}

输出/错误：

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException:empty String
at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
at sun.misc.FloatingDecimal.parseDouble(Unknown Source)
at java.lang.Double.parseDouble(Unknown Source)
at Conv$3.keyTyped(Conv.java:101)
at java.awt.Component.processKeyEvent(Unknown Source)
at javax.swing.JComponent.processKeyEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

错误消息中的第一行包含： java.lang.NumberFormatException:empty String这意味着您尝试将空字符串""转换为从未填充的文本字段中获得的数字。

---

堆栈跟踪中提到您的代码的第一行是：

at Conv$3.keyTyped(Conv.java:101)

我猜它在这里：

   textField2.addKeyListener(new KeyAdapter() {
          public void keyTyped(KeyEvent e2) {
              textField1.setText("");
                textField3.setText("");  
                Double d1,d2,d3;
                d2 = Double.parseDouble(textField2.getText()); // line 101

您需要将textField2.getText()提取到 local变量并检查它是否确实包含一个数字。