java组件JTree问题

Question

//给树的子节点 添加了单机监听事件后，

//怎么使其选择单机的节点页面置顶，以及单机的页面不论点击多少次，始终只实例化一次

tree.addMouseListener(new MouseAdapter() {
   public void mouseClicked(final MouseEvent arg0) {
    TreePath tp = tree.getSelectionPath();
    if( tp == null){
     JOptionPane.showMessageDialog(null,
       "请点击选择按钮");
     return;
     }
    System.out.println(tp);
    String str = tp.toString();
    String[] arr = str.split(",");
    str = arr[arr.length-1].trim();
    str = str.substring(0, str.length()-1);
    if(str.equals("开户")){
     
     BankAddFrame addl = new BankAddFrame();
     desktopPane.add(addl);
     
    }else if(str.equals("挂失")){
     BankLossFrame loss = new BankLossFrame();
     desktopPane.add(loss);
    }else if(str.equals("注销")){
     BankCloseFrame close = new BankCloseFrame();
     desktopPane.add(close);
    }else if(str.equals("个人业务")){
     BankPerFrame per = new BankPerFrame();
     desktopPane.add(per);
    }else if(str.equals("贷款")){
     BankLoanFrame loan = new BankLoanFrame();
     desktopPane.add(loan);
    }   
   }
  });