How to make a drop-down box in java?

A friend is worried because of some problems when doing Java-related development. For example, this question, how to make a drop-down box in java? This article will tell you how to implement a drop-down box in Java. Friends who are interested can learn about it.

The referenced packages are:

java.awt is a software package that contains all categories for creating user interfaces and drawing graphical images. In AWT terminology, user interface objects such as buttons or scroll bars are called components.

javax.swing The most commonly used pachage, contains classes for various swing components

javax.swing.border contains classes related to the outer frame of swing components

import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;
 
import java.awt.event.*;
public class Test extends JFrame {
    private JPanel jPane;//大的面板
    private JTextField textField;//文本框
    public JComboBox comboBox;//下拉选择框
    public static String a =null;
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Test frame = new Test();
                    frame.setVisible(true);
//              设置窗口可见
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
  
    /**
     * Create the frame.
     */
    public Test() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//      EXIT_ON_CLOSE相当于执行System.exit(0);的动作方法退出应用程序，关闭进程
//      如果不写这句话点击X我们也能关闭窗口，但是在后台进程里面我们会发现我们的进程数并不减少
        setBounds(200, 200, 400, 400);//首次点开，发现距离屏幕左边,上方200，长宽均为400
        jPane = new JPanel();
        jPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(jPane);
        jPane.setLayout(null);
//按照规定的位置显示，否则按照默认的FlowLayout（每个JPanel对象初始化时都使用FlowLayout布局，）布局显示的
          
        comboBox = new JComboBox();
        String[] select = {"选项一","选项二","选项三"};
//        添加选项值
        comboBox.setModel(new DefaultComboBoxModel(select));
        comboBox.setBounds(15, 15, 100, 25);
        jPane.add(comboBox);
      
        textField = new JTextField();
        textField.setBounds(150, 15, 76, 22);
        jPane.add(textField);
        textField.setText("选项一");
    
        comboBox.addItemListener(new ItemListener() {
            @Override
            public void itemStateChanged(ItemEvent e) {
                if(e.getStateChange() == ItemEvent.SELECTED) {
                     textField.setText(comboBox.getSelectedItem().toString());
                     a = textField.getText();
                     System.out.print(a);
                }
            }  
        });
    }
}

Related learning recommendations: java basic tutorial

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