如何在Java中创建多个下拉框？我想在这些代码行后面添加另一个下拉框

Question

    JFrame frame = new JFrame("Recipes"); 
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(500, 500);
    frame.setLocation(430, 100);

    JPanel panel = new JPanel();

    frame.add(panel);

    JLabel lbl = new JLabel("Select time taken");
    lbl.setVisible(true);

    panel.add(lbl);

    String[] choices = { "10 MINS","15 MINS", "20 MINS","25 MINS","30 MINS"};

    final JComboBox<String> cb = new JComboBox<String>(choices);

    cb.setVisible(true);
    panel.add(cb);
    
    JButton btn = new JButton("OK");
    panel.add(btn);`

我不知道该添加什么之后，我尝试添加另一个标签和组合框，但它没有工作

Answer 1

确保frame.setvisible（true）；在最后一行

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

public class Test01 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        JFrame frame = new JFrame("Recipes"); 
        //frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500, 500);
        frame.setLocation(430, 100);

        JPanel panel = new JPanel();

        frame.add(panel);

        JLabel lbl = new JLabel("Select time taken");
        lbl.setVisible(true);

        panel.add(lbl);

        String[] choices = { "10 MINS","15 MINS", "20 MINS","25 MINS","30 MINS"};

        final JComboBox<String> cb = new JComboBox<String>(choices);

        cb.setVisible(true);
        panel.add(cb);
        
        JButton btn = new JButton("OK");
        panel.add(btn);
        
        frame.setVisible(true);
    }

}