Java如何侦听JComboBox中所选项目的更改？
此示例演示ItemListener侦听JComboBox组件中所选项目的更改。
package org.nhooo.example.swing;
import javax.swing.*;
import javax.swing.border.BevelBorder;
import java.awt.event.ItemListener;
import java.awt.event.ItemEvent;
import java.awt.*;
public class ComboBoxSelectionChange extends JFrame {
public ComboBoxSelectionChange() {
initialize();
}
private void initialize() {
setSize(300, 300);
setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
setLayout(new FlowLayout(FlowLayout.LEFT));
String[] items = new String[] {"A", "B", "C", "D", "E", "F"};
JComboBox<String> comboBox = new JComboBox<>(items);
final JTextArea textArea = new JTextArea(5, 15);
textArea.setBorder(new BevelBorder(BevelBorder.LOWERED));
//用于收听组合框中所选项目的更改
//我们需要向组合框组件添加一个ItemListener，如图所示
//下面。
comboBox.addItemListener(new ItemListener() {
//侦听是否已选择组合框的新项目。
public void itemStateChanged(ItemEvent event) {
JComboBox comboBox = (JComboBox) event.getSource();
//受事件影响的项目。
Object item = event.getItem();
textArea.setText("Affected items: " + item.toString());
if (event.getStateChange() == ItemEvent.SELECTED) {
textArea.setText(item.toString() + " selected.");
}
if (event.getStateChange() == ItemEvent.DESELECTED) {
textArea.setText(item.toString() + " deselected.");
}
}
});
getContentPane().add(comboBox);
getContentPane().add(textArea);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new ComboBoxSelectionChange().setVisible(true);
}
});
}
}