java - JButton 不显示

Question

嗨，有人知道为什么我的“button1”不显示吗？当我执行该程序时，我似乎无法弄清楚它一切正常并成功运行，但它不显示此按钮。任何帮助将不胜感激，谢谢。

private Container c;
private JPanel gridPanel;
private JComboBox combo;
final JLabel label = new JLabel();
private JButton button1 = new JButton("Clear");
private JButton button2 = new JButton("Exit");

/**
 * Christopher Haddad - 559815X
 */
public Planets() {
    c = getContentPane();
    gridPanel = new JPanel();
    gridPanel.setLayout(new GridLayout(5, 0, 0, 0));

    label.setVisible(true);

    combo = new JComboBox(); 
    combo.setEditable(false);
    combo.addItem("No Planet Selected");
    combo.addItem("Mercury"); 
    combo.addItem("Venus"); 
    combo.addItem("Earth"); 
    gridPanel.add(combo);

    add(button1);
    add(button2);
    button1.addActionListener(this);
    button2.addActionListener(this);

    c.add(gridPanel, BorderLayout.NORTH);
    setTitle("Planet Diameter"); 
    setSize(700, 250);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

    combo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent event) {

            JComboBox comboBox = (JComboBox) event.getSource();

            Object select = comboBox.getSelectedItem();

            if(select.toString().equals("No Planet Selected"))
                label.setText("");
            else if(select.toString().equals("Mercury"))
                label.setText("The planet Mercury is 3100kms in diameter");
            else if(select.toString().equals("Venus"))
                label.setText("The planet Venus is 7500kms in diameter");
            else if (select.toString().equals("Earth"))
                label.setText("The planet Earth is 8000kms in diameter");

        }
    });
    getContentPane().add(combo);
    getContentPane().add(label);
}

    // event handling method, implementing the actionPerformed method of ActionListener 
    public void actionPerformed(ActionEvent e) 
    { 
        // set the button label to number of times it has been clicked
        if(e.getSource() == button1) {
            label.setText(" ");
        }
        else if(e.getSource() == button2) {
            System.exit(0);
        }
    } 

Answer 1

很难确定，但我假设您将内容直接添加到顶级容器，例如JFrame

JFrame 使用 BorderLayout 作为默认布局管理器，因此使用

add(button1);
add(button2);

基本上是说，添加 button1到CENTER位置，然后添加 button2到 CENTER 位置。 BorderLayout 只允许单个组件存在于特定位置。

首先尝试将按钮添加到另一个面板...