问答题 本题的功能是对列表项的操作，包括删除、添加和反选。窗口中有两个列表框和5个按钮，按钮标签代表着移除列表项的方向，“＞”代表只移除选中的列表项，“＞＞”代表移除所有的列表项，“!”代表反向选择列表项。
import jav

• a.awt.*;
  import java.awt.event.*;
  class java3 extends Frame implements ActionListener&ItemListener
  final static int ITEMS=10;
  List ItList=new List(ITEMS,true);
  List rtList=new List(0,true);
  java3()
  super("java3");
  addWindowListener(new WindowAdapter()
  public void windowClosing(WindowEvent e)
  System.exit(0);
  
  );
  GridBagLayout gbl=new GridBagLayout();
  setLayout(gbl);
  add(ItList,0,0,1,5,1.0,1.0);
  add(rtList,2,0,1,5,1.0,1.0);
  ItList.addActionListener(this);
  ItList.addItemListener(this);
  rtList.addActionListener(this);
  rtList.addItemListener(this);
  Button b;
  add(b=new Button("＞"),1,0,1,1,0,1.0);
• b.addActionListener(this);
  add(b=new Button("＞＞"),1,1,1,1,0,1.0);b.addActionListener(this);
  add(b=new Button("＜"),1,2,1,1,0,1.0);b.addActionListener(this);
  add(b=new Button("＜＜"),1,3,1,1,0,1.0);b.addActionListener(this);
  add(b=Flew Button("!"),1,4,1,1,0,1.0);b.addActionListener(this);
  for(int i=0;i＜ITEMS;i++)
  ltList.add("item"+i);
  
  pack();
  show();
  
  void add(Component comp,
  int x,int y,int w,int h,double weightx,double weighty)
  GridBagLayout gbl=(GridBagLayout)getLayout();
  GridBagConstraints c=new GridBagConstraints();
• c.fill=GridBagConstraints.BOTH;c.gridx=x;c.gridy=y;c.gridwidth=w;c.gridheight=h;c.weightx=weightx;c.weighty=weighty;
  add(comp);
  gbl.setConstraints(comp,c);
  
  void reverseSelections(List 1)
  for(int i=0;i＜1.length();i++)
  if(l.isIndexSelected(i))
  l.deselect(i);
  else
  l.select(i);
  
  
  
  void deselectAll(List 1)
  for(int i=0;i＜1.getItemCount();itt)
  l.deselect(i);
  
  
  void replaceItem(List 1,String item)
  for(int i=0;i＜1.getItemCount();i+t)
  if(1.getItem(i).equals(item))
  l.replaceItem(item +"*",i);
  
  
  
  void move(List l1,List 12,boolean all)
  if(all)
  for(int i=0;i＜l1.getItemCount();i++)
  l2.add(l1.getItem(i));
  
  l1.removeAll();
  else
  String[]items=l1.getSelectedItems();
  int[]itemIndexes=l1.getSelectedIndexes();
  deselectAll(l2);
  for(int i=0;i＜items.length;i++)
  l2.add(items[i]);
  l2.select(l2.getItemCount()=1);
  if(i==0)
  l2.makeVisible(l2.getItemCount()=1);
  
  
  for(int i=itemIndexes.length-1;i＞=0;i--)
  l1.remove(itemIndexes[i]);
  
  
  
  public void actionPerformed(ActionEvent evt)
  String arg=evt.getActionCommand();
  if("＞".equals(arg))
  move(ltList,rtList,false);
  else if("＞＞".equals(arg))
  move(ltList,rtList,true);
  else if("＜".equals(arg))
  move(rtList,ltList,false);
  else if("＜＜".equals(arg))
  move(rtList,ltList,true);
  else if("!".equals(arg))
  if(ltList.getSelectedItems().length＞0)
  reverseSelections(ltList);
  else if(rtList.getSelectedItems().length＞0)
  reverseSelections(rtList);
  
  else
  Object target=evt.getSource();
  if(target==rtList || target==ItList)
  replaceItem((List)target,arg);
  
  
  
  public void itemStatedChanged(ItemEvent ent)
  List target=(List)evt.getSource();
  if(target==ltList)
  deselectAll(rtList);
  else if(target==rtList)
  deselectAll(ltList);
  
  
  public static void main(String[]args)
  new java3();