如何使JComboBox的下拉部分比它自己的框宽啊？原来默认是一样宽的!(高分）

比较笨的方法：
public void actionPerformed(ActionEvent event) {
        UI ui = new UI();
        jComboBox1.setUI(ui);
        ((Popup)ui.getPopup()).setDisplaySize(100, 50);
    }    class UI extends javax.swing.plaf.basic.BasicComboBoxUI {
        protected javax.swing.plaf.basic.ComboPopup createPopup() {
            Popup popup = new Popup( comboBox );
            popup.getAccessibleContext().setAccessibleParent(comboBox);
            return popup;
        }
        public javax.swing.plaf.basic.ComboPopup getPopup() {
            return popup;
        }
    }    class Popup extends javax.swing.plaf.basic.BasicComboPopup {
        public Popup(JComboBox combo) {
            super(combo);
        }
        public void setDisplaySize(int width, int height) {
            scroller.setSize(width, height);
            scroller.setPreferredSize(new Dimension(width, height));
        }
        public void show() {
            setListSelection(comboBox.getSelectedIndex());
            Point location = getPopupLocation();
            show( comboBox, location.x, location.y );
        }
        private void setListSelection(int selectedIndex) {
            if ( selectedIndex == -1 ) {
                list.clearSelection();
            }
            else {
                list.setSelectedIndex( selectedIndex );
                list.ensureIndexIsVisible( selectedIndex );
            }
        }
        
        private Point getPopupLocation() {
            Dimension popupSize = comboBox.getSize();
            Insets insets = getInsets();            // reduce the width of the scrollpane by the insets so that the popup
            // is the same width as the combo box.
            popupSize.setSize(popupSize.width - (insets.right + insets.left),
                              getPopupHeightForRowCount( comboBox.getMaximumRowCount()));
            Rectangle popupBounds = computePopupBounds( 0, comboBox.getBounds().height,
                popupSize.width, popupSize.height);
            Dimension scrollSize = popupBounds.getSize();
            Point popupLocation = popupBounds.getLocation();//            scroller.setMaximumSize( scrollSize );
//            scroller.setPreferredSize( scrollSize );
//            scroller.setMinimumSize( scrollSize );            list.revalidate();
            
            return popupLocation;
        }
    }