java - 为什么中间的栏不显示？

Question

我正在用 Java 制作一个简单的计算器 GUI，以开始学习如何使用 Java。以下代码不起作用。仅出现第一列。第二列和第三列去哪里？

    package Start;


    import java.awt.*;
    import javax.swing.*;       

    public class CalculatorGUI {

public static void addComponentsToPane(Container pane) {

    pane.setLayout(new GridBagLayout());
    GridBagConstraints c = new GridBagConstraints();
    c.fill = GridBagConstraints.HORIZONTAL;

    JLabel label;
    JButton button;

    label = new JLabel("I'm a calculator");
    c.gridwidth = GridBagConstraints.REMAINDER;
    c.weightx = 0.0;
    c.gridx = 0;
    c.gridy = 0;
    pane.add(label, c);

    button = new JButton("1");
    c.gridx = 0;
    c.gridy = 1;
    pane.add(button, c);

    button = new JButton("2");
    c.gridx = 1;
    c.gridy = 1;
    pane.add(button, c);

    button = new JButton("3");
    c.gridx = 2;
    c.gridy = 1;
    pane.add(button, c);

    button = new JButton("4");
    c.gridx = 0;
    c.gridy = 2;
    pane.add(button, c);

    button = new JButton("5");
    c.gridx = 1;
    c.gridy = 2;
    pane.add(button, c);

    button = new JButton("6");
    c.gridx = 2;
    c.gridy = 2;
    pane.add(button, c);

    button = new JButton("7");
    c.gridx = 0;
    c.gridy = 3;
    pane.add(button, c);

    button = new JButton("8");
    c.gridx = 1;
    c.gridy = 3;
    pane.add(button, c);

    button = new JButton("9");
    c.gridx = 2;
    c.gridy = 3;
    pane.add(button, c);


}

public static void createAndShowGUI() {
    JFrame frame = new JFrame("CalculatorGUI");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

   addComponentsToPane(frame.getContentPane());

    frame.pack();
    frame.setVisible(true);
}

public static void main(String[] args) {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI();
        }
    });
  }
}

我尝试让标签只写c.gridwidth = 3;，但这做了同样的事情。当我将宽度设为 1 时，所有按钮都会出现，但标签仅位于一个单元格中。 如何使标签跨越 3 列？而不使其他按钮消失。

Answer 1

How do i make the label span 3 columns without gridwidth?

c.gridwidth = 3;

然后，您需要在添加其他组件之前将其重置为 1。

so that it is centered over the '2' button

您还需要设置标签的文本对齐方式:

label.setHorizontalAlignment(JLabel.CENTER);