Java Swing银行存取款窗口代码报错，try/catch放置位置是否正确？

问题排查 #

你的代码存在以下几类明确错误：

• 语法结构错误：actionPerformed方法、第二个main方法直接定义在initialize方法内部，Java不允许方法嵌套定义普通方法；末尾多余多个闭合大括号；重复定义了两次main方法。
• 作用域错误：
  • 余额变量balance、余额显示标签totalBalance是initialize方法的局部变量，事件回调逻辑无法正常访问，需要提升为类的成员变量
  • 三个按钮绑定的都是空的ActionListener，你写的actionPerformed逻辑没有和按钮做绑定
• 依赖缺失：没有导入javax.swing.JOptionPane，调用弹窗时会报错
• 变量引用错误：调用JOptionPane.showMessageDialog时第一个参数写了不存在的变量f，应该用当前的frame对象作为父窗口
• 命名错误：类名是acmeBank，第二个main方法里实例化写的是ACMEBank，Java大小写敏感，找不到对应类

修正后的完整代码 #

import java.awt.EventQueue;
import java.awt.Font;
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.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;
import javax.swing.LayoutStyle.ComponentPlacement;

// 类名遵循Java规范改为大驼峰
public class AcmeBank {
    private JFrame frame;
    private JTextField creditInput;
    private JTextField debitInput;
    // 提升为成员变量
    private double balance = 0;
    private JLabel totalBalance;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    AcmeBank window = new AcmeBank();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public AcmeBank() {
        initialize();
    }

    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 470, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JLabel lblNewLabel = new JLabel("DEPOSIT");
        lblNewLabel.setFont(new Font("Tahoma", Font.PLAIN, 14));
        
        JLabel lblNewLabel_1 = new JLabel("WITHDRAWAL");
        lblNewLabel_1.setFont(new Font("Tahoma", Font.PLAIN, 14));
        
        creditInput = new JTextField();
        creditInput.setColumns(10);
        
        debitInput = new JTextField();
        debitInput.setColumns(10);
        
        JButton creditButton = new JButton("CREDIT");
        JButton debitButton = new JButton("DEBIT");
        JButton clearButton = new JButton("CLEAR");
        
        // 统一绑定监听器
        ActionListener listener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                if (e.getSource() == creditButton) {
                    try {
                        double amount = Double.parseDouble(creditInput.getText());
                        balance += amount;
                        totalBalance.setText(String.valueOf(balance));
                    } catch (NumberFormatException ee) {
                        JOptionPane.showMessageDialog(frame, "请输入合法数字");
                    }
                } else if (e.getSource() == debitButton) {
                    try {
                        double amount = Double.parseDouble(debitInput.getText());
                        if(amount > balance) {
                            JOptionPane.showMessageDialog(frame, "余额不足");
                            return;
                        }
                        balance -= amount;
                        totalBalance.setText(String.valueOf(balance));
                    } catch (NumberFormatException ee) {
                        JOptionPane.showMessageDialog(frame, "请输入合法数字");
                    }
                } else if (e.getSource() == clearButton) {
                    debitInput.setText("");
                    creditInput.setText("");
                }
            }
        };
        creditButton.addActionListener(listener);
        debitButton.addActionListener(listener);
        clearButton.addActionListener(listener);
        
        JLabel lblNewLabel_2 = new JLabel("BALANCE    $");
        lblNewLabel_2.setFont(new Font("Tahoma", Font.PLAIN, 14));
        
        totalBalance = new JLabel("0");
        GroupLayout groupLayout = new GroupLayout(frame.getContentPane());
        groupLayout.setHorizontalGroup(
            groupLayout.createParallelGroup(Alignment.LEADING)
                .addGroup(groupLayout.createSequentialGroup()
                    .addGroup(groupLayout.createParallelGroup(Alignment.TRAILING, false)
                        .addGroup(groupLayout.createSequentialGroup()
                            .addGap(47)
                            .addComponent(lblNewLabel_2)
                            .addPreferredGap(ComponentPlacement.RELATED)
                            .addComponent(totalBalance, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
                        .addGroup(Alignment.LEADING, groupLayout.createSequentialGroup()
                            .addGap(18)
                            .addGroup(groupLayout.createParallelGroup(Alignment.LEADING)
                                .addComponent(lblNewLabel, Alignment.TRAILING)
                                .addComponent(lblNewLabel_1, Alignment.TRAILING))
                            .addGap(0)
                            .addGroup(groupLayout.createParallelGroup(Alignment.LEADING, false)
                                .addComponent(debitInput, Alignment.TRAILING)
                                .addComponent(creditInput, Alignment.TRAILING, GroupLayout.DEFAULT_SIZE, 124, Short.MAX_VALUE))))
                    .addPreferredGap(ComponentPlacement.RELATED, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addGroup(groupLayout.createParallelGroup(Alignment.LEADING)
                        .addComponent(debitButton, GroupLayout.PREFERRED_SIZE, 76, GroupLayout.PREFERRED_SIZE)
                        .addComponent(creditButton, GroupLayout.PREFERRED_SIZE, 80, GroupLayout.PREFERRED_SIZE))
                    .addGap(18)
                    .addComponent(clearButton, GroupLayout.PREFERRED_SIZE, 78, GroupLayout.PREFERRED_SIZE)
                    .addContainerGap(39, Short.MAX_VALUE))
        );
        groupLayout.setVerticalGroup(
            groupLayout.createParallelGroup(Alignment.LEADING)
                .addGroup(groupLayout.createSequentialGroup()
                    .addGroup(groupLayout.createParallelGroup(Alignment.LEADING)
                        .addGroup(groupLayout.createSequentialGroup()
                            .addGap(23)
                            .addGroup(groupLayout.createParallelGroup(Alignment.BASELINE)
                                .addComponent(lblNewLabel)
                                .addComponent(creditInput, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                                .addComponent(creditButton))
                            .addGap(11)
                            .addGroup(groupLayout.createParallelGroup(Alignment.BASELINE)
                                .addComponent(lblNewLabel_1)
                                .addComponent(debitInput, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                                .addComponent(debitButton)))
                        .addGroup(groupLayout.createSequentialGroup()
                            .addGap(40)
                            .addComponent(clearButton)))
                    .addGap(33)
                    .addGroup(groupLayout.createParallelGroup(Alignment.TRAILING)
                        .addComponent(lblNewLabel_2)
                        .addComponent(totalBalance, GroupLayout.PREFERRED_SIZE, 26, GroupLayout.PREFERRED_SIZE))
                    .addContainerGap(122, Short.MAX_VALUE))
        );
        frame.getContentPane().setLayout(groupLayout);
    }
}

内容的提问来源于stack exchange，提问作者FingerLessB