Adding Items to and Removing Items from a List

The ListDemo example that we showed previously features a list whose contents can change. You can find the source code for ListDemo in ListDemo.java. Here is the ListDemo code that creates a mutable list model object, puts the initial items in it, and uses the list model to create a list:

listModel = new DefaultListModel();
listModel.addElement("Debbie Scott");
listModel.addElement("Scott Hommel");
listModel.addElement("Alan Sommerer");

list = new JList(listModel);

This particular program uses an instance of DefaultListModel, a class provided by Swing. In spite of the class name, a list does not have a DefaultListModel unless your program explicitly makes it so. If DefaultListModel does not suit your needs, you can write a custom list model, which must adhere to the ListModel interface.

The following code snippet shows the actionPerformed method for the action listener registered on the Fire button. The bold line of code removes the selected item in the list. The remaining lines in the method disable the fire button if the list is now empty, and make another selection if it is not.

public void actionPerformed(ActionEvent e) {
   int index = list.getSelectedIndex();
   listModel.remove(index);

   int size = listModel.getSize();

   if (size == 0) { //Nobody's left, disable firing.
       fireButton.setEnabled(false);

   } else { //Select an index.
       if (index == listModel.getSize()) {
           //removed item in last position
           index--;
       }

       list.setSelectedIndex(index);
       list.ensureIndexIsVisible(index);
   }
}

Here is the actionPerformed method for the action listener shared by the Hire button and the text field:

public void actionPerformed(ActionEvent e) {
   String name = employeeName.getText();

   //User did not type in a unique name...
   if (name.equals("") || alreadyInList(name)) {
       Toolkit.getDefaultToolkit().beep();
       employeeName.requestFocusInWindow();
       employeeName.selectAll();
       return;
   }

   int index = list.getSelectedIndex(); //get selected index
   if (index == -1) { //no selection, so insert at beginning
       index = 0;
   } else {           //add after the selected item
       index++;
   }

   listModel.insertElementAt(employeeName.getText(), index);

   //Reset the text field.
   employeeName.requestFocusInWindow();
   employeeName.setText("");

   //Select the new item and make it visible.
   list.setSelectedIndex(index);
   list.ensureIndexIsVisible(index);
}

This code uses the list model's insertElementAt method to insert the new name after the current selection or, if no selection exists, at the beginning of the list. If you just wish to add to the end of the list, you can use DefaultListModel's addElement method instead.

Whenever items are added to, removed from, or modified in a list, the list model fires list data events. Refer to How to Write a List Data Listener for information about listening for these events. That section contains an example that is similar to ListDemo, but adds buttons that move items up or down in the list.