JComboBox显示长项目的内容

如果JComboBox列表中的内容过长的话，下拉框中不全部显示
解决方法一：当鼠标放在这个过长的项目中时显示tooltip，提示用户选择这项的全部信息
setComboBoxUI(combobox);

private void setComboBoxUI(final JComboBox combobox) {
        combobox.setUI(new WindowsComboBoxUI() {
            protected ComboPopup createPopup() {
                return new BasicComboPopup(combobox) {
                    protected JList createList() {
                        return new JList(comboBox.getModel()) {
                            public void processMouseEvent(MouseEvent e) {
                                if (e.isControlDown()) {
                                    e = new MouseEvent((Component) e.getSource(), e.getID(), e.getWhen(),
                                            e.getModifiers() ^ InputEvent.CTRL_MASK, e.getX(), e.getY(),
                                            e.getClickCount(), e.isPopupTrigger());
                                }
                                super.processMouseEvent(e);
                            }
      
                            public String getToolTipText(MouseEvent event) {
                                int index = locationToIndex(event.getPoint());
                                if (index != -1) {
                                    Object value = getModel().getElementAt(index);
                                    ListCellRenderer renderer = getCellRenderer();
                                    Component rendererComp =
                                            renderer.getListCellRendererComponent(this, value, index, true, false);
                                    if (rendererComp.getPreferredSize().width > getVisibleRect().width) {
                                        return value == null ? null : value.toString();
                                    } else {
                                        return null;
                                    }
                                }
                                return null;
                            }
      
                            public Point getToolTipLocation(MouseEvent event) {
                                int index = locationToIndex(event.getPoint());
                                if (index != -1) {
                                    Rectangle cellBounds = getCellBounds(index, index);
                                    return new Point(cellBounds.x, cellBounds.y);
                                }
                                return null;
                            }
                        };
                    }
                };
            }
        });
    }

解决方法二：获取最大长项目宽度，并设置为弹出下拉框时的宽度
combobox.setUI(new LargerComboBoxUI());

class LargerComboBoxUI extends BasicComboBoxUI {
        protected ComboPopup createPopup() {
            return new LargerComboPopup(comboBox);
        }
      
        public class LargerComboPopup extends BasicComboPopup {
            public LargerComboPopup(JComboBox comboBox) {
                super(comboBox);
            }
      
            public void show() {
                int selectedIndex = comboBox.getSelectedIndex();
                if (selectedIndex == -1) {
                    list.clearSelection();
                } else {
                    list.setSelectedIndex(selectedIndex);
                    list.ensureIndexIsVisible(selectedIndex);
                }
      
                Insets insets = getInsets();
                Dimension listDim = list.getPreferredSize();
                boolean hasScrollBar = scroller.getViewport().getViewSize().height != listDim.height;
                if (hasScrollBar) {
                    JScrollBar scrollBar = scroller.getVerticalScrollBar();
                    listDim.width += scrollBar.getPreferredSize().getWidth();
                }
      
                int width = Math.max(listDim.width, comboBox.getWidth() - (insets.right + insets.left));
                int height = getPopupHeightForRowCount(comboBox.getMaximumRowCount());
                Rectangle popupBounds = computePopupBounds(0, comboBox.getHeight(), width, height);
      
                Dimension scrollSize = popupBounds.getSize();
                scroller.setMaximumSize(scrollSize);
                scroller.setPreferredSize(scrollSize);
                scroller.setMinimumSize(scrollSize);
      
                list.revalidate();
                show(comboBox, popupBounds.x, popupBounds.y);
            }
        }
    }