Question

我尝试使用以下代码：

 public class JComboBoxDemo extends JFrame{
    private JPanel panelParents;
    private JLabel lblTitle;
    private JComboBox cboLanguage;

public JComboBoxDemo() {
    super("JComboBox Demo");
    setContentPane(panelParents);

    String language[] = {"English","Khmer","Korea","Chinese","Thai","Russia"};

    cboLanguage = new JComboBox(language);
    cboLanguage.setSelectedIndex(1);
    cboLanguage.setMaximumRowCount(5);

    pack();
    setBounds(100,100,450,256);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setLocationRelativeTo(null);
}
}

但它在JComboBox中没有显示任何内容，我的代码有什么问题？

Answer 1

问题是您正在将null传递给setContentPane。下面的代码正在运行

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class JComboBoxDemo1 extends JFrame {
    private JPanel panelParents;
    private JLabel lblTitle;
    private JComboBox cboLanguage;

    public JComboBoxDemo1() {
        super("JComboBox Demo");

        String language[] = {"English", "Khmer", "Korea", "Chinese", "Thai",
                "Russia"};

        cboLanguage = new JComboBox(language);
        cboLanguage.setSelectedIndex(1);
        cboLanguage.setMaximumRowCount(5);
        getContentPane().add(cboLanguage);

        pack();
        setBounds(100, 100, 450, 256);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
    }

    public static void main(String[] args) {
        new JComboBoxDemo1();
    }
}

Answer 2

以下是第二种方法。理想情况下，如果不扩展它的功能，则不应覆盖类。 首选合成而不是继承 ，详情为here。可以找到JFrame个详细信息here

以下代码：

import java.awt.Component;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class JComboBoxDemo {
    private JPanel panelParents;
    private JLabel lblTitle;

    public JComboBoxDemo() {
        JFrame frame = new JFrame("JComboBox Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(getMainComponent());
        frame.pack();
        frame.setBounds(100, 100, 450, 256);
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);
    }

    private Component getMainComponent() {
        JComboBox cboLanguage = new JComboBox();
        String language[] = {"English", "Khmer", "Korea", "Chinese", "Thai",
                "Russia"};
        cboLanguage = new JComboBox(language);
        cboLanguage.setSelectedIndex(1);
        cboLanguage.setMaximumRowCount(5);
        return cboLanguage;
    }

    public static void main(String[] args) {
        new JComboBoxDemo();
    }
}

JComboBox不显示数据？

2 个答案: