使用 JTextField 问题的 Java 计算器程序

Question

import java.awt.Font;
import java.awt.GridLayout;

import javax.swing.JPanel;
import javax.swing.JTextField;

public class CalField extends JPanel {
    private JTextField field;

    public CalField() {

        setLayout(new GridLayout(1, 1, 5, 5));
        field = new JTextField(20);
        field.setFont(new Font("SansSerif", Font.PLAIN, 20));
        field.setEditable(true);
        add(field);

    }

    public JTextField getField() {
        return field;
    }

    public void setField(String text) {
        field.setText(text);
        System.out.print(text);

    }
}

CalButton 类:

import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JPanel;

public class CalButton extends JPanel {
    private JButton[] buttons;
    private static final String[] buttonNames = { "7", "8", "9", "/", "4", "5",
            "6", "*", "1", "2", "3", "-", "0", ".", "=", "+" };
    private CalField calField;

    public CalButton() {
        buttons = new JButton[buttonNames.length];
        setLayout(new GridLayout(4, 4, 3, 3));
        calField = new CalField();
        ButtonListener handler = new ButtonListener();
        for (int i = 0; i < buttonNames.length; i++) {
            buttons[i] = new JButton(buttonNames[i]);
            buttons[i].setFont(new Font("SansSerif", Font.BOLD, 20));

            add(buttons[i]);
            buttons[i].addActionListener(handler);
        }

    }

    private class ButtonListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent event) {
            // TODO Auto-generated method stub

            if (buttons[0].getActionCommand() == event.getActionCommand()) {
                calField.setField(event.getActionCommand());
//              System.out.print(buttons[0].getActionCommand());
            } else if (buttons[1].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[1].getActionCommand());
            } else if (buttons[2].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[2].getActionCommand());
            } else if (buttons[3].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[3].getActionCommand());
            } else if (buttons[4].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[4].getActionCommand());
            } else if (buttons[5].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[5].getActionCommand());
            } else if (buttons[6].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[6].getActionCommand());
            } else if (buttons[7].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[7].getActionCommand());
            } else if (buttons[8].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[8].getActionCommand());
            } else if (buttons[9].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[9].getActionCommand());
            } else if (buttons[10].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[10].getActionCommand());
            } else if (buttons[11].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[11].getActionCommand());
            } else if (buttons[12].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[12].getActionCommand());
            } else if (buttons[13].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[13].getActionCommand());
            } else if (buttons[14].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[14].getActionCommand());
            } else if (buttons[15].getActionCommand() == event
                    .getActionCommand()) {
                System.out.print(buttons[15].getActionCommand());
            }
        }
    }
}

计算器类:

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingConstants;

public class Calculator {
    public static void main(String[] args) {

        JFrame application = new JFrame("Calculator");
        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.setSize(250, 200);

        CalField calField = new CalField();
        CalButton calButton = new CalButton();

        application.add(calField, BorderLayout.PAGE_START);
        application.add(calButton, BorderLayout.CENTER);

        application.setVisible(true);
    }
}

在这个程序中，在JButton的 actionListener 我称之为 CalField 类的 setText()在JTextField中设置相应按钮文本的方法.

但控制台中显示的文本却未显示在 TextField 中.我现在能做什么？请帮助我。

Answer 1

因此，在您的 Calculator 类中，您创建一个 CalField 实例并将其添加到 JFrame...

public class Calculator {
    public static void main(String[] args) {

        JFrame application = new JFrame("Calculator");
        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.setSize(250, 200);

        CalField calField = new CalField();
        CalButton calButton = new CalButton();

        application.add(calField, BorderLayout.PAGE_START);
        application.add(calButton, BorderLayout.CENTER);

        application.setVisible(true);
    }
}

然后，在您的 CalButton 类中，您创建了 CalField 的另一个实例...

public class CalButton extends JPanel {
    //...
    private CalField calField;

    public CalButton() {
        //...
        calField = new CalField();
        //...
    }

这永远不会添加到任何东西，而是您尝试更新的实例。此 CalField 实例与您添加到框架的 CalField 实例无关。

相反，您需要将 CalField 的实例传递给 CalButton

public class CalButton extends JPanel {
    //...
    private CalField calField;

    public CalButton(CalField calField) {
        //...
        this.calField = calField;
        //...
    }

然后在您的Calculator 类中，您会将创建的CalField 实例传递给CalButton 实例...

CalField calField = new CalField();
CalButton calButton = new CalButton(calField);

application.add(calField, BorderLayout.PAGE_START);
application.add(calButton, BorderLayout.CENTER);

这创建了实际显示在屏幕上的类之间的关系

Now when i clicking on a button this shows the text but when i click another button it overrides the previous one's text. How to solve this problem so that the overriding does'nt occur

那是因为 setText 就是这样做的，它设置字段的文本，替换之前的内容。

相反，当您调用 setField 时，您应该在字段中追加新的下一个文本，例如...

public void setField(String text) {
    field.setText(field.getText() + text);
    System.out.print(text);

}

但我可能会将该方法更改为 appendField，以便清楚它的作用

此外，因为 actionPerformed 中的大部分 if-else 语句实际上并没有做任何事情，它们所做的几乎是同一件事，

if (buttons[0].getActionCommand() == event.getActionCommand()) {
    calField.setField(event.getActionCommand());
} else if (buttons[1].getActionCommand() == event.getActionCommand()) {
    System.out.print(buttons[1].getActionCommand());
} else if (buttons[2].getActionCommand() == ...

你可以做一些更像...

calField.setField(event.getActionCommand());

现在，您可能需要为特殊键添加一些if语句，例如=和clear，但所有其他数字按钮，只需要执行上述操作，这应该会大大减少重复的代码，让代码维护起来更容易