关于JComboBox的事件触发的问题;来者必有分!!!

下面是源代码
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class ComboBoxTest extends JFrame{
    private JLabel sqlLabel = new JLabel("SQL:");
    private JComboBox sqlComboBox = new JComboBox();
    public ComboBoxTest() {
        sqlComboBox.setEditable(true);
        sqlComboBox.addItem("");
        sqlComboBox.setBackground(Color.WHITE);
        sqlComboBox.setPreferredSize(new Dimension(500,25));
        sqlComboBox.addItemListener(new ItemListener() {
            public void itemStateChanged(ItemEvent event) {
                if (event.getStateChange() == ItemEvent.SELECTED){
                    if(sqlComboBox.getSelectedIndex()==-1){
                        String currentSQL=(String)event.getItem();
                        System.out.println("currentSQL : "+currentSQL);
                        sqlComboBox.addItem(currentSQL);
                    }
                }
            }
        });
        
        Container cp=getContentPane();
        cp.setLayout(new FlowLayout());
        cp.add(sqlLabel);
        cp.add(sqlComboBox);
        pack();
        setVisible(true);
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent evt) {
                System.exit(0);
            }
        });
    }
    
    public static void main(String[] args){
        new ComboBoxTest();
    }
}我得意图是让用户在JComboBox里写sql语句,当用户按回车时发送sql语句,并且把发送过的sql语句
用addItem()添加到JComboBox里,但是现在有一个问题:
当我连续敲击一次以上的回车时,为什么只能触发一次itemStateChanged,(我希望用户每次按回车都能触发一次itemStateChanged)
还有当选择了JComboBox里的被记录的sql后,再按回车却无法触发itemStateChanged;
谁能帮我解决这个问题