程序添加JComboBox的item也能触发itemStateChanged事件吗

程序添加JComboBox的item也能触发itemStateChanged事件吗

直接看实例:

Java代码  

1. package share;  
2.   
3. import java.awt.EventQueue;  
4. import java.awt.GridBagConstraints;  
5. import java.awt.GridBagLayout;  
6. import java.awt.Insets;  
7. import java.awt.event.ItemEvent;  
8. import java.awt.event.ItemListener;  
9.   
10. import javax.swing.JButton;  
11. import javax.swing.JComboBox;  
12. import javax.swing.JFrame;  
13. import javax.swing.JPanel;  
14. import javax.swing.border.EmptyBorder;  
15.   
16. import com.string.widget.util.ValueWidget;  
17.   
18. public class TestJComboBox extends JFrame {  
19.   
20.     private JPanel contentPane;  
21.     private JComboBox<String> comboBox;  
22.   
23.     /** 
24.      * Launch the application. 
25.      */  
26.     public static void main(String[] args) {  
27.         EventQueue.invokeLater(new Runnable() {  
28.             public void run() {  
29.                 try {  
30.                     TestJComboBox frame = new TestJComboBox();  
31.                     frame.setVisible(true);  
32.                 } catch (Exception e) {  
33.                     e.printStackTrace();  
34.                 }  
35.             }  
36.         });  
37.     }  
38.   
39.     /** 
40.      * Create the frame. 
41.      */  
42.     public TestJComboBox() {  
43.         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
44.         setBounds(100, 100, 450, 300);  
45.         contentPane = new JPanel();  
46.         contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));  
47.         setContentPane(contentPane);  
48.         GridBagLayout gbl_contentPane = new GridBagLayout();  
49.         gbl_contentPane.columnWidths = new int[]{0, 0, 0};  
50.         gbl_contentPane.rowHeights = new int[]{0, 0};  
51.         gbl_contentPane.columnWeights = new double[]{1.0, 0.0, Double.MIN_VALUE};  
52.         gbl_contentPane.rowWeights = new double[]{0.0, Double.MIN_VALUE};  
53.         contentPane.setLayout(gbl_contentPane);  
54.           
55.         comboBox = new JComboBox<String>();  
56.         GridBagConstraints gbc_comboBox = new GridBagConstraints();  
57.         gbc_comboBox.insets = new Insets(0, 0, 0, 5);  
58.         gbc_comboBox.fill = GridBagConstraints.HORIZONTAL;  
59.         gbc_comboBox.gridx = 0;  
60.         gbc_comboBox.gridy = 0;  
61.         contentPane.add(comboBox, gbc_comboBox);  
62.           
63.         JButton btnAddItem = new JButton("add item");  
64.         GridBagConstraints gbc_btnAddItem = new GridBagConstraints();  
65.         gbc_btnAddItem.gridx = 1;  
66.         gbc_btnAddItem.gridy = 0;  
67.         contentPane.add(btnAddItem, gbc_btnAddItem);  
68.           
69.           
70.         comboBox.addItemListener(new ItemListener()  
71.         {  
72.             @Override  
73.             public void itemStateChanged(ItemEvent arg0)  
74.             {  
75.                 System.out.println("itemStateChanged");  
76.             }  
77.         });  
78.         init222();  
79.           
80.     }  
81.     private void init222(){  
82.         comboBox.addItem("a");  
83.         comboBox.addItem("b");  
84.         comboBox.addItem("c");  
85.     }  
86.   
87. }  

启动的时候,控制台打印:

itemStateChanged

说明启动之后,执行了itemStateChanged 方法,说明了触发了itemStateChanged 事件.

总结:程序添加addItem 也能触发itemStateChanged 事件

如何把init222 方法放在comboBox.addItemListener 前就不会触发itemStateChanged 事件