Working JList And ScrollPane in Java

Abhishek Dubey
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Article

Introduction of JList

In this article we are going to describe how to use JList and JScrollPane in an application. JList is a component that displays a group of items to the user and allows him/her to select one or more items from the list. A listModel(interface) is used for maintaining the contents of the the list. A class DefaultListModel(inherits ListModel) is used for maintaining a contents list. This class actually provides methods to add removeAll elements or a specific elements list and to find the index of an element. A component that allows the user to select one or more objects from a list. A separate model, ListModel, represents the contents of the list. It's easy to display an array or vector of objects, using a JList constructor that builds a ListModel instance for you. A List doesn't support scrolling directly. To create a scrolling list you make the JList the viewport view of a JScrollPane. By default the JList selection model allows any combination of items to be selected at a time, using the constant MULTIPLE_INTERVAL_SELECTION. The selection state is actually managed by a separate delegate object, an instance of ListSelectionModel. However JList provides convenient properties for managing the selection.

Note - JJList doesn't provide any special support for handling double or triple (or N) mouse clicks however it's easy to handle them using a MouseListener. Use the JList method locationToIndex() to determine what cell was clicked.

Example

import javax.swing.*;

import javax.swing.event.ListSelectionEvent;

import javax.swing.event.ListSelectionListener;

import java.awt.*;

import java.awt.event.*;

public class JListExample extends JFrame

{

JList list;

String[] listColorNames = { "BLACK", "BLUE", "GREEN", "YELLOW","WHITE" };

Color[] listColorValues = { Color.BLACK, Color.BLUE, Color.GREEN,Color.YELLOW, Color.WHITE };

Container contentpane;

public JListExample()

{

super("List Example ");

contentpane = getContentPane();

contentpane.setLayout(new FlowLayout());

list = new JList(listColorNames);

list.setSelectedIndex(0);

list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

contentpane.add(new JScrollPane(list));

list.addListSelectionListener(new ListSelectionListener()

{

public void valueChanged(ListSelectionEvent e)

{

contentpane.setBackground(listColorValues[list.getSelectedIndex()]);

}

});

setSize(300, 300);

setVisible(true);

}

public static void main(String[] args)

{

JListExample test = new JListExample();

test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

Output

Cmd output

First or initial output.

When you select the BLUE item of the list.

When you select GREEN item on list.

Introduction of JScrollPane

JScollPane manages a viewport, optional vertical and horizontal scroll bars, and optional row and column heading viewports. The JViewport provides a window, or "viewport" onto a data source -- for example, a text file. That data source is the "scrollable client" (aka data model) displayed by the JViewport view. A JScrollPane basically consists of JScrollBars, a JViewport, and the wiring between them, as shown in the following diagram.