JTextField 输入异常检查和输入问题 return

Question

我有这个调用 JFrame 并在返回该输入之前请求输入的代码。

代码如下：

import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.GroupLayout;
import javax.swing.GroupLayout.Alignment;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.LayoutStyle.ComponentPlacement;

public class testing1 {

    public JFrame frame;
    public JTextField textField;
    String keyword;
    ClickHandler cl = new ClickHandler();
    JTextArea messageText;
    String NumberUnits;

    public static void main(String[] args) {
        testing1 t = new testing1();
        int NUnits = t.AskUnits(); 
        System.out.println("Number of Units: " + NUnits);   
    }

    private testing1() {
        frame = new JFrame();
        frame.getContentPane().setBackground(Color.WHITE);
        
        JPanel questionPanel = new JPanel();
        questionPanel.setBackground(Color.WHITE);
        
        textField = new JTextField();
        textField.setColumns(10);
        
        JPanel panel = new JPanel();
        panel.setBackground(Color.WHITE);
        GroupLayout groupLayout = new GroupLayout(frame.getContentPane());
        groupLayout.setHorizontalGroup(
            groupLayout.createParallelGroup(Alignment.LEADING)
                .addGroup(groupLayout.createSequentialGroup()
                    .addGap(99)
                    .addGroup(groupLayout.createParallelGroup(Alignment.LEADING)
                        .addGroup(groupLayout.createSequentialGroup()
                            .addGap(10)
                            .addComponent(textField, GroupLayout.DEFAULT_SIZE, 210, Short.MAX_VALUE)
                            .addGap(11))
                        .addComponent(questionPanel, GroupLayout.DEFAULT_SIZE, 231, Short.MAX_VALUE))
                    .addGap(106))
                .addGroup(groupLayout.createSequentialGroup()
                    .addGap(132)
                    .addComponent(panel, GroupLayout.PREFERRED_SIZE, 173, GroupLayout.PREFERRED_SIZE)
                    .addContainerGap(131, Short.MAX_VALUE))
        );
        groupLayout.setVerticalGroup(
            groupLayout.createParallelGroup(Alignment.LEADING)
                .addGroup(groupLayout.createSequentialGroup()
                    .addContainerGap(38, Short.MAX_VALUE)
                    .addComponent(questionPanel, GroupLayout.PREFERRED_SIZE, 69, GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(ComponentPlacement.UNRELATED)
                    .addComponent(textField, GroupLayout.PREFERRED_SIZE, 19, GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(ComponentPlacement.RELATED)
                    .addComponent(panel, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                    .addGap(90))
        );
        
        messageText = new JTextArea();
        questionPanel.add(messageText);
        
        JButton okButton = new JButton("OK");
        okButton.setBackground(Color.WHITE);
        okButton.addActionListener(cl);
        okButton.setActionCommand("ok");
        panel.add(okButton);
        
        JButton cancelButton = new JButton("CANCEL");
        cancelButton.setBackground(Color.WHITE);
        cancelButton.addActionListener(cl);
        cancelButton.setActionCommand("cancel");
        panel.add(cancelButton);
        frame.getContentPane().setLayout(groupLayout);
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        frame.setVisible(true);
    }
    
    public int AskUnits() {
        keyword = "AskUnits";
        messageText.setText("How many units are in this course?");
        NumberUnits = textField.getText(); 
//      String NumberUnits = JOptionPane.showInputDialog(null, "How many units are in this course?", courseName, JOptionPane.INFORMATION_MESSAGE);
            try {
                   int NumberofUnits = Integer.parseInt(NumberUnits); 
                    if (NumberofUnits < 0 || NumberofUnits > 100) {
                        JOptionPane.showMessageDialog(null, "Input out of bounds",
                                  "ERROR", JOptionPane.ERROR_MESSAGE);
                        System.exit(0);
                    }
                    return NumberofUnits;
                 } catch(NumberFormatException e) {
                    JOptionPane.showMessageDialog(null, "Input is not a number",
                              "ERROR", JOptionPane.ERROR_MESSAGE);
                    System.exit(0);
                 }
            return 0; 
    } // all clear
    
    public class ClickHandler implements ActionListener {
        public void actionPerformed(ActionEvent event) {
            String yourChoice = event.getActionCommand();
            
            switch(keyword) {
            case "AskUnits":
                switch(yourChoice) {
                case "ok": System.out.println("OK GOT"); break;
                case "cancel": System.exit(0); break;
                }
                break;
            }
        }
    }
}

我对这段代码的问题：

甚至在输入代码之前，“INPUT IS NOT A NUMBER”异常就出现了。
我想在打印出从输入接收到的 NUnits 值之前接收输入 NUnits。但是，NUnits 在输入任何内容之前打印 0。

Answer 1

抛出异常是因为您在程序启动后立即调用 AskUnits()，这会启动输入处理而不给用户输入值的机会。如果您将 AskUnits() 方法调用移动到您的点击处理程序中，用户将有机会输入一个值，您可以在单击 OK 后将其打印到控制台。

如果您使用 AskUnits() 方法来设置屏幕（要问的问题等），您至少应该移动输入处理代码（下面的所有内容，包括 NumberUnits = textField.getText()调用）到一个单独的方法，然后您可以从 OK 按钮的点击处理程序调用该方法以打印输入的值。

@camickr 对 Java 命名约定给出了一些很好的建议。这是来自 Oracle 的一个很好的资源，它也涵盖了所有其他程序标识符。该页面已存档，但约定未更改。

来自Code Conventions for the Java Programming Language

Naming conventions make programs more understandable by making them easier to read.

大多数 SO 成员欣赏的东西，这反过来又使问题更有可能在此处获得帮助。

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