java - 计算器编码错误。请更正

Question

我曾尝试使用 Java 中的 GUI 编写一个简单的计算器，但被这段代码困住了，并反复收到“输入有效数字”的消息。我愿意接受建议。建议我的代码中可能的更正。我认为我错误地使用了 java 的 try 和 check 异常功能。

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JTextField;
import java.awt.BorderLayout;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JLabel;
import javax.swing.JOptionPane;

import java.awt.Font;
import javax.swing.SwingConstants;

public class FIRSTCALC {

private JFrame frame;
private JTextField txtfield1;
private JTextField txtfield2;
private JTextField textfieldans;

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

/**
 * Create the application.
 */
public FIRSTCALC() {
    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);

    txtfield1 = new JTextField();
    txtfield1.setHorizontalAlignment(SwingConstants.LEFT);
    txtfield1.setText("ENTER NUMBER 1 : ");
    txtfield1.setBounds(28, 11, 178, 68);
    frame.getContentPane().add(txtfield1);
    txtfield1.setColumns(10);

    txtfield2 = new JTextField();
    txtfield2.setHorizontalAlignment(SwingConstants.LEFT);
    txtfield2.setText("ENTER NUMBER 2 : ");
    txtfield2.setBounds(228, 11, 175, 68);
    frame.getContentPane().add(txtfield2);
    txtfield2.setColumns(10);

    JButton btnNewButton = new JButton("ADD");
    btnNewButton.setToolTipText("TO ADD NUMBERS");
    btnNewButton.setFont(new Font("Sitka Text", Font.BOLD, 16));
    btnNewButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            int num1,num2,sum;
            try
            {
                num1=Integer.parseInt(txtfield1.getText());
                num2=Integer.parseInt(txtfield2.getText());
                sum=num1+num2;
                textfieldans.setText(Integer.toString(sum));
            }
            catch(Exception e1)
            {
                JOptionPane.showMessageDialog(null, "ENTER VALID NUMBER");
            }
        }
    });
    btnNewButton.setBounds(61, 121, 120, 42);
    frame.getContentPane().add(btnNewButton);

    JButton btnNewButton_1 = new JButton("SUBTRACT");
    btnNewButton_1.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            int num1,num2,sum;
            try
            {
                num1=Integer.parseInt(txtfield1.getText());
                num2=Integer.parseInt(txtfield2.getText());
                sum=num1-num2;
                textfieldans.setText(Integer.toString(sum));
            }
            catch(Exception e1)
            {
                JOptionPane.showMessageDialog(null, "ENTER VALID NUMBER");
            }   
        }
    });
    btnNewButton_1.setToolTipText("TO SUBTRACT NUMBERS");
    btnNewButton_1.setFont(new Font("Sitka Text", Font.BOLD, 16));
    btnNewButton_1.setBounds(251, 121, 128, 42);
    frame.getContentPane().add(btnNewButton_1);

    JLabel lblNewLabel = new JLabel("THE ANSWER IS :");
    lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
    lblNewLabel.setFont(new Font("Sitka Text", Font.BOLD, 18));
    lblNewLabel.setBounds(28, 192, 193, 58);
    frame.getContentPane().add(lblNewLabel);

    textfieldans = new JTextField();
    textfieldans.setBounds(251, 196, 109, 48);
    frame.getContentPane().add(textfieldans);
    textfieldans.setColumns(10);
}

}

Answer 1

您显然会遇到异常，因为您正在将输入的数字附加或添加到已包含在其中一个 JTextField 中的文本中。当尝试使用 Integer.parseInt() 方法将 JTextField 中包含的字符串解析为整数值时，这会生成 NumberFormatException 。如果提供除数字之外的任何内容，则将引发此异常。您只是让异常显示一个消息框，指示用户“输入有效数字”。

如果您想将文本保留在文本字段组件中，请应用焦点监听器来突出显示组件中当前的文本，以便在用户输入数字时它会被覆盖。一般来说，这个前置文本是浅灰色的。这是一个例子:

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;
import javax.swing.SwingConstants;

public class FIRSTCALC {

    private JFrame frame;
    private JTextField txtfield1;
    private JTextField txtfield2;
    private JTextField textfieldans;

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

    /**
     * Create the application.
     */
    public FIRSTCALC() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setAlwaysOnTop(true);
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        txtfield1 = new JTextField("Enter First Number");
        txtfield1.setForeground(Color.lightGray);
        // Add a Focus Listener to txtfield1
        txtfield1.addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                txtfield1.selectAll();
            }

            @Override
            public void focusLost(FocusEvent e) { 
                txtfield1.setForeground(Color.black);
            }
        });
        txtfield1.setHorizontalAlignment(SwingConstants.CENTER);
        txtfield1.setBounds(28, 11, 178, 68);
        txtfield1.setColumns(10);
        frame.getContentPane().add(txtfield1);

        txtfield2 = new JTextField("Enter Second Number");
        txtfield2.setForeground(Color.lightGray);
        // Add a Focus Listener to txtfield2
        txtfield2.addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                txtfield2.selectAll();
            }

            @Override
            public void focusLost(FocusEvent e) {
                txtfield2.setForeground(Color.black);
            }
        });
        txtfield2.setHorizontalAlignment(SwingConstants.CENTER);
        txtfield2.setBounds(228, 11, 175, 68);
        txtfield2.setColumns(10);
        frame.getContentPane().add(txtfield2);

        JButton btnNewButton = new JButton("ADD");
        btnNewButton.setToolTipText("TO ADD NUMBERS");
        btnNewButton.setFont(new Font("Sitka Text", Font.BOLD, 16));
        btnNewButton.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e) {
                int num1, num2, sum;
                try {
                    num1 = Integer.parseInt(txtfield1.getText());
                    num2 = Integer.parseInt(txtfield2.getText());
                    sum = num1 + num2;
                    textfieldans.setText(Integer.toString(sum));
                }
                catch (NumberFormatException ex) {
                    JOptionPane.showMessageDialog(frame, "<html><center>The following formula:<br><br>"
                                + "<font size='4' color=red>" + txtfield1.getText() + 
                                "</font> + <font size='4' color=red>"+ txtfield2.getText() + 
                                "</font><br><br>contains invalid digits!</center></html>");
                }
            }
        });
        btnNewButton.setBounds(61, 121, 120, 42);
        frame.getContentPane().add(btnNewButton);

        JButton btnNewButton_1 = new JButton("SUBTRACT");
        btnNewButton_1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                int num1, num2, sum;
                try {
                    num1 = Integer.parseInt(txtfield1.getText());
                    num2 = Integer.parseInt(txtfield2.getText());
                    sum = num1 - num2;
                    textfieldans.setText(Integer.toString(sum));
                }
                catch (NumberFormatException ex) {
                    JOptionPane.showMessageDialog(frame, "<html><center>The following formula:<br><br>"
                                + "<font size='4' color=red>" + txtfield1.getText() + 
                                "</font> - <font size='4' color=red>"+ txtfield2.getText() + 
                                "</font><br><br>contains invalid digits!</center></html>");
                }
            }
        });
        btnNewButton_1.setToolTipText("TO SUBTRACT NUMBERS");
        btnNewButton_1.setFont(new Font("Sitka Text", Font.BOLD, 16));
        btnNewButton_1.setBounds(251, 121, 128, 42);
        frame.getContentPane().add(btnNewButton_1);

        JLabel lblNewLabel = new JLabel("THE ANSWER IS :");
        lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
        lblNewLabel.setFont(new Font("Sitka Text", Font.BOLD, 18));
        lblNewLabel.setBounds(28, 192, 193, 58);
        frame.getContentPane().add(lblNewLabel);

        textfieldans = new JTextField();
        textfieldans.setHorizontalAlignment(SwingConstants.CENTER);
        textfieldans.setBounds(251, 196, 109, 48);
        textfieldans.setColumns(10);
        frame.getContentPane().add(textfieldans);
        frame.setLocationRelativeTo(null);

    }

}