Question

当我运行程序时，我得到弹出框，当我输入number1或number2中的数字时，异常处理在我点击“输入”-key之前给出了“仅允许的数字”错误。它一直这样做，直到我在两个文本字段中填写了一个数字。除非我在文本字段中添加除数字以外的其他内容，否则不应该给我错误。也。我无法从CM转换为INCH两次，它会再次给我错误。我必须在从CM转换为INCH和INCH转换为CM之间切换。它转换得很好，所以问题必须是设置异常处理的问题？这就像它在我输入之前读取文本字段，因此它给了我一个错误，因为没有插入数字。

任何人都可以帮助我吗？提前谢谢！

//丹尼尔

我有两节课。

第1课的代码：

package inchcm;

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class InchCM extends JFrame {

    private JTextField num1 = new JTextField(8);
    private JTextField num2 = new JTextField(8);
    private JLabel l1 = new JLabel();
    private JLabel l2 = new JLabel();

    public InchCM() {


        setLayout(new BorderLayout());

        //panel 1 med GridLayout (2,0) til 2 x JTextField(8).
        JPanel p1 = new JPanel(new GridLayout(2, 0));
        p1.add(new JLabel(""));
        p1.add(num1);
        p1.add(new JLabel(""));
        p1.add(num2);


        JPanel p2 = new JPanel(new GridLayout(2, 0));
        p2.add(new JLabel(" Inches"));
        p2.add(l1);
        p2.add(new JLabel(" Centimeters"));
        p2.add(l2);


        add(p1, BorderLayout.EAST);
        add(p2, BorderLayout.WEST);


        num1.addKeyListener(
                new KeyAdapter() {

                    public void keyReleased(KeyEvent e) {

                        try {

                            double nummer1 = Double.parseDouble(num1.getText());
                            double nummer2 = Double.parseDouble(num2.getText());

                            Udregning udr = new Udregning(nummer1, nummer2);


                            if (e.getKeyCode() == KeyEvent.VK_ENTER) {
                                num2.setText(String.format("%.2f", udr.inchtocm()));
                            }                            
                        } 
                        //end tal i et af JTextFieldsne.
                        catch (NumberFormatException ex) {
                            System.out.println(ex);
                            JOptionPane.showMessageDialog(null,
                                    "Only numbers allowed \nTry again",
                                    "Input error", JOptionPane.ERROR_MESSAGE);
                        }
                    }
                });



        num2.addKeyListener(
                new KeyAdapter() {                    

                    public void keyReleased(KeyEvent e) {

                        try {
                            //objekt af num1 og num2.
                            double nummer1 = Double.parseDouble(num1.getText());
                            double nummer2 = Double.parseDouble(num2.getText());

                            Udregning udr = new Udregning(nummer1, nummer2);


                            if (e.getKeyCode() == KeyEvent.VK_ENTER) {
                                num1.setText(String.format("%.2f", udr.cmtoinch()));
                            }                            
                        } 

                        catch (NumberFormatException ex) {
                            System.out.println(ex);
                            JOptionPane.showMessageDialog(null,
                                    "Only numbers allowed \nTry againn",
                                    "Input error", JOptionPane.ERROR_MESSAGE);
                        }
                    }
                });

    }

    public static void main(String[] args) {


        InchCM frame = new InchCM();
        frame.pack();
        frame.setTitle("InchCM");
        frame.setSize(300, 130);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

第2课的代码： “计算类”

package inchcm;

public class Udregning {

    private double num1 = 0;
    private double num2 = 0;

    Udregning() {
    }

    Udregning(double newnum1, double newnum2) {
        setnum1(newnum1);
        setnum2(newnum2);
    }

    private void setnum1(double newnum1) {
        num1 = newnum1;
    }

    private void setnum2(double newnum2) {
        num2 = newnum2;
    }

    public double inchtocm() {
        double result;
        result = num1 * 2.54;
        return result;
    }

    public double cmtoinch() {
        double result;
        result = num2 * .39;
        return result;
    }
}

Answer 1

正如我最近自己在这里学到的，没有必要KeyListener来实现这种行为。您应该向ActionListener添加JTextField，当在文本字段内推送ENTER时将触发该KeyListener。

如果要触发另一个键的操作，然后按ENTER键，则应使用键绑定而不是{{1}}。请参阅Swing tutorial

Answer 2

每次触发KeyReleased事件时都会执行try catch块 - 即每次按键。在尝试解析输入数字之前，您需要更改它以检查VK_ENTER：

try {
    if (e.getKeyCode() == KeyEvent.VK_ENTER) {
        double nummer1 = Double.parseDouble(num1.getText());
        double nummer2 = Double.parseDouble(num2.getText());

        Udregning udr = new Udregning(nummer1, nummer2);
        num2.setText(String.format("%.2f", udr.inchtocm()));
    }                            
} 
//end tal i et af JTextFieldsne.
catch (NumberFormatException ex) {
    System.out.println(ex);
    JOptionPane.showMessageDialog(null,
            "Only numbers allowed \nTry again",
            "Input error", JOptionPane.ERROR_MESSAGE);
}

Answer 3

我同意@mcfinnigan的回答，但是在num1的事件处理程序中你不应该对num2做出反应。如果您想更新每个密钥：

 num1.addKeyListener(
            new KeyAdapter() {

                public void keyReleased(KeyEvent e) {

                    try {
                        double nummer1 = Double.parseDouble(num1.getText());

                        // Synchronize both fields:
                        try {
                            double nummer2 = Double.parseDouble(num2.getText());

                            Udregning udr = new Udregning(nummer1, nummer2);
                            //if (e.getKeyCode() == KeyEvent.VK_ENTER) {
                                num2.setText(String.format("%.2f", udr.inchtocm()));
                            //}                            
                        } catch (NumberFormatException ex2) { }


                    } 
                    //end tal i et af JTextFieldsne.
                    catch (NumberFormatException ex) {
                        System.out.println(ex);
                        JOptionPane.showMessageDialog(null,
                                "Only numbers allowed \nTry again",
                                "Input error", JOptionPane.ERROR_MESSAGE);
                    }
                }
            });

异常处理“只允许数字”，在我输入之前出错。为什么？

3 个答案: