JList And JScrollPane in Java

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 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.

 

 

 

Example

import javax.swing.*;
public class JScrollPaneDemo
{
    public static void main(String[] args)
    {
        String st = "Amit Maheswari\n"
            +
            "Akshay Tewatiya\n"
            +
            "Praveen Kumar\n"
            +
            "Vipendra kumar\n"
            +
            "Arjun Pawar"
            +
            "sanjoli\n" + "Deepak Dwij"
            +
            "Amit\n" + "Anuj\n"
            +
            "Sourabh Tripathi\n" + "Vaibhav Tripathi\n"
            +
            "Anamika" + "KRIShana\n"
            +
            "I have four cars and two computers.";
        JFrame frame = new JFrame("Example a JScrollPane ");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel();
        JTextArea area = new JTextArea(st, 8, 12);
        JScrollPane spane = new JScrollPane(area);
        panel.add(spane);
        frame.add(panel);
        frame.setSize(400, 400);
        frame.setVisible(true);
    }
}

Output

 

 

 

Resources

• Describing the Java Packages
• Garbage Collector in .NET
• Use of ByteStreams and CharacterStreams in JAVA
• Describing the JSF Elements
• Learning JDBC (Java Database Connectivity)