Thread: Why does JList use Vectors?

Out of curiosity, does anyone know why JList allows you to only set the data via an Object array or an Object Vector (unless you make your own ListModel and such)? Why a Vector<Object> instead of the more generic List<Object>? They must have had a good reason for this.

Interesting question. Same could be asked for JTable, JComboBox, etc... My understanding is that Swing was available prior to the introduction of Collections, at a time when Vector was the only 'List' available. List was probably never introduced as an option because implementation of your own model allows you the flexibility to use any data structure you wish.

Vector is synchronized, so I could see an argument for preferring it over unsynchronized ArrayLists. You can modify the Vector that you pass in to the JList constructor, since the constructor just refers to the Vector directly:

    public JList(final Vector<? extends E> listData) {
        this (
            new AbstractListModel<E>() {
                public int getSize() { return listData.size(); }
                public E getElementAt(int i) { return listData.elementAt(i); }
            }
        );
    }

Since you're using Vector, in theory you can modify the Vector from any Thread without weird stuff happening.

However, from my testing, you need to call JList.updateUI() after you modify it anyway, so I don't see any huge benefits from this approach:

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Vector;
 
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
 
public class JListTest {
 
	public JListTest(){
 
		final JFrame frame = new JFrame ("JList Test");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		final Vector<String> v = new Vector<String>();
		v.add("one");
		v.add("two");
		v.add("three");
 
		final JList<String> list = new JList<String>(v);
 
		JButton button = new JButton("Add");
		button.addActionListener(new ActionListener(){
			public void actionPerformed(ActionEvent e){
				v.add("four");
				list.updateUI();
			}
		});
 
		frame.add(new JScrollPane(list), BorderLayout.CENTER);
		frame.add(button, BorderLayout.SOUTH);
 
		frame.pack();
		frame.setVisible(true);
	}
 
	public static void main(String [] args){
		new JListTest();
	}
}

So I don't know. This might be a remnant of AWT which is supposed to be thread-safe, but it's often a bit of a waste of time to focus too much on these kinds of questions.

Also, from the DefaultListModel API:

This class loosely implements the java.util.Vector API, in that it implements the 1.1.x version of java.util.Vector, has no collection class support, and notifies the ListDataListeners when changes occur. Presently it delegates to a Vector, in a future release it will be a real Collection implementation.