（转）
package comboBox;

import java.awt.Dimension;
import java.util.Vector;

import javax.swing.ComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;

public class WideComboBox extends JComboBox {

 public WideComboBox() {
 }

 public WideComboBox(final Object items[]) {
  super(items);
 }

 public WideComboBox(Vector items) {
  super(items);
 }

 public WideComboBox(ComboBoxModel aModel) {
  super(aModel);
 }

 private boolean layingOut = false;

 public void doLayout() {
  try {
   layingOut = true;
   super.doLayout();
  } finally {
   layingOut = false;
  }
 }

 public Dimension getSize() {
  Dimension dim = super.getSize();
  if (!layingOut)
   dim.width = Math.max(dim.width, getPreferredSize().width);
  return dim;
 }

 public static void main(String[] args) {
  JFrame jf = new JFrame();
  WideComboBox wc = new WideComboBox(new String[] { "11111111111111",
    "22222222222222", "333" });
  jf.getContentPane().add(wc);
  jf.setVisible(true);
 }
}