Question

我正在制作一个目前有两个班级的计算器。第一个是扩展JFrame并创建计算器框架的主类，另一个是为JFrame创建按钮布局的类。我希望能够将ButtonPanel类中的文本设置为包含文本区域的主类，但是当我让ButtonPanel类扩展主类时，它扩展了JFrame它会导致这些错误。

Exception in thread "main" java.lang.StackOverflowError
at sun.awt.Win32GraphicsConfig.getBounds(Native Method)
at sun.awt.Win32GraphicsConfig.getBounds(Unknown Source)
at java.awt.Window.init(Unknown Source)
at java.awt.Window.<init>(Unknown Source)
at java.awt.Frame.<init>(Unknown Source)
at javax.swing.JFrame.<init>(Unknown Source)

我的代码

public class Calculator extends JFrame {
    public Calculator() {
        super("Calculator");
        setSize(300,200);
        setResizable(false);
        setLocationRelativeTo(null);

        textBox = new JTextField();
        getContentPane().add(textBox,BorderLayout.NORTH);

        getContentPane().add(new ButtonPanel(), BorderLayout.CENTER);
        setVisible(true);

    }
    protected JTextField textBox;
    public void setString(String str) {
        textBox.setText(str);
    }

    public static void main(String[] args) {
        Calculator ge = new Calculator();
    }
}

class ButtonPanel extends Calculator {

    ButtonPanel() {
        JPanel pan = new JPanel();
        GridBagLayout gbl = new GridBagLayout();
        pan.setLayout(gbl);
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.fill = GridBagConstraints.HORIZONTAL;

        gbc.gridx = gbc.gridy = 0;
        gbc.gridheight = gbc.gridwidth = 1;
        JButton button = new JButton("7");
        pan.add(button,gbc);
        button.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent event) {
                    int num = 7;
                    performAct(num);
                }
            });

        gbc.gridx = 1;
        button = new JButton("8");
        pan.add(button, gbc);
        button.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent event) {
                    int num = 8;
                    performAct(num);
                }
            });

        //Other Buttons not included
        void performAct(int buttonNum) {
            switch (buttonNum) {
            case 0: setString("0");
            case 1: setString("1");
            case 2: setString("2");
            case 3: setString("3");
            case 4: setString("4");
            case 5: setString("5");
            case 6: setString("6");
            case 7: setString("7");
            case 8: setString("8");
            case 9: setString("9");
            case 10: setString(" + ");
            case 11: setString( " - ");
            case 12: setString(" * ");
            case 13: setString( " / ");
            case 14: setString(" % ");
            }
        }
    }

Answer 1

 class ButtonPanel extends Calculator

ButtonPanel不应该扩展计算器。 ButtonPanel不是JFrame。

ButtonPanel可以扩展JPanel，因为你想向它添加组件。

JPanel pan = new JPanel();

然后就不需要创建JPanel了。您只需设置类的布局并直接添加组件。

查看How to Use GridBagLayout上Swing教程中的部分，了解如何构建课程的更好示例。

扩展一个类后的StackOverflowError，其父类扩展了JFrame

1 个答案: