I have this problem:

1) There are objects placed in the TreeMap through the JTextField. (Phonebook-like program).

2)There are buttons that implement view of available records in TreeMap. When you click on these buttons next / previous available objects of TreeMap displaying in JTextField. (scroll through the available records).

I tried this code, but I didn't work :/

btn[4].addActionListener(new ActionListener(){
     Iterator iter = tree.keySet().iterator();
      public void actionPerformed(ActionEvent e) {
         if (iter.hasNext()){
         String str = iter.next().toString();
         fldFio.setText(str);
         fldNumber.setText(tree.get(str));
         }
      }
});