FocusListener不是JComboBox的适当监听器，另外一个监听器可以创建无限循环（尤其是可编辑的JComboBox），
的FocusListener是异步的，有时是太难捕捉事件是正确的订单特别是在案件JComponents增加了另一个侦听器（S）太
示例如何从派生收听Focus
JTextField/ JFormattedTextField
import java.awt.*;import java.awt.event.*;import javax.swing.*;public class ComboBoxTwo extends Jframe implements ItemListener { private static final long serialVersionUID = 1L; private JComboBox mainComboBox; private JComboBox subComboBox; public ComboBoxTwo() { String[] items = {"Select Item", "Color", "Shape", "Fruit"}; String[] subItems1 = {"Select Color", "Red", "Blue", "Green"}; mainComboBox = new JComboBox(items); mainComboBox.addItemListener(this); mainComboBox.addFocusListener(fcsListener); add(mainComboBox, BorderLayout.WEST); subComboBox = new JComboBox(subItems1); subComboBox.setPrototypeDisplayValue("XXXXXXXXXXXXXXXXXXX"); subComboBox.addItemListener(this); add(subComboBox, BorderLayout.EAST); } @Override public void itemStateChanged(ItemEvent e) { if (e.getStateChange() == ItemEvent.SELECTED) { if (e.getSource() == mainComboBox) { System.out.println("Source : mainComboBox"); } else if (e.getSource() == subComboBox) { System.out.println("Source : subComboBox"); } } } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { Jframe frame = new ComboBoxTwo(); frame.setDefaultCloseOperation(EXIT_ON_CLOSE); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } }); }// private FocusListener fcsListener = new FocusListener() { @Override public void focusGained(FocusEvent e) { dumpInfo(e); } @Override public void focusLost(FocusEvent e) { dumpInfo(e); } private void dumpInfo(FocusEvent e) { System.out.println("Source : " + name(e.getComponent())); System.out.println("Opposite : " + name(e.getOppositeComponent())); System.out.println("Temporary: " + e.isTemporary()); final Component c = e.getComponent();//works for editable JComboBox too if (c instanceof JFormattedTextField) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { ((JFormattedTextField) c).selectAll(); } }); } else if (c instanceof JTextField) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { ((JTextField) c).selectAll(); } }); } } private String name(Component c) { return (c == null) ? null : c.getName(); } };}
