为什么 JComboBox 在鼠标 hover 上触发 toString()？

Question

I have created a simple GUI, one JComboBox and JButton. JButton populate the JComboBox with objects of class testString. When mouse hover the JComboBox it fired toString() of testString class almost 25 time. Why this happening? How we can stop it?

here is code:

import javax.swing.DefaultComboBoxModel;

public class _NewJFrame extends javax.swing.JFrame {

public _NewJFrame() {
    initComponents();
}

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    
    Object[] args = {new testString("ABC") , new testString("EDF") , "GIH", "IJK"}; 
    jComboBox1.setModel(new DefaultComboBoxModel(args ));
}                                        
public static void main(String args[]) {
        

            new _NewJFrame().setVisible(true);
            
             
}

private javax.swing.JButton jButton1;
private javax.swing.JComboBox<String> jComboBox1;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JTextArea jTextArea1;
}



class testString {
String text; 
static int i; 
testString(String text){ this.text = text; }; 


public String toString(){
    System.out.println("ToSting() Called on Text " + text + " "+ ++i);

    return text; 
}


}

GUI output

Answer 1

You can't stop the JComboBox from calling the toString() method of your items.

This is because the JComboBox needs to know what text it has to show to the user.

For this it calls the toString() method of the items (of the currently shown item on mouse-over, of all items when the drop down list).

Answer 2

@Thomas

I have tried the following but results are same.

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    
    
    Object[] args = {new testString("ABC") , new testString("EDF") }; 
    jComboBox1.setModel(new DefaultComboBoxModel(args ));
    
    
    
    
    jComboBox1.setRenderer(new DefaultListCellRenderer() {
@Override
public Component getListCellRendererComponent(JList list,
                                           Object value,
                                           int index,
                                           boolean isSelected,
                                           boolean cellHasFocus) {
    testString employee = (testString)value;
    value = employee.mytoString();
    return super.getListCellRendererComponent(list, value,
            index, isSelected, cellHasFocus);
}
});