A basic JTree example

Let us demonstrate a simple creation of a Tree application, TreeExample.java:

• we will create a simple tree (Fig ) containing only a few items and having no ability to add or remove items.
• we will include a scrollable pane, which will become more important as we add features to our application.
• The icons shown in this example are defaults provided by Swing.
• We do not actually insert an items in the tree. When no specific data model has been specified, JTree reverts to a default example model which is impractical but useful for this demonstration.
• When the program is executed, notice that the tree is initially collapsed down to the root level.
• Opening the root expands it, showing the next level of indentation -- Notice the change in icon for the lowest element of the tree.
• This is the default operation for the simple tree.

The full code listing for TreeExample.java is as follows:

// Imports
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class TreeExample
		extends 	JFrame
 {
	// Instance attributes used in this example
	private	JPanel		topPanel;
	private	JTree		tree;
	private	JScrollPane scrollPane;

	// Constructor of main frame
	public TreeExample()
	{
		// Set the frame characteristics
		setTitle( "Simple Tree Application" );
		setSize( 300, 100 );
		setBackground( Color.gray );

		// Create a panel to hold all other components
		topPanel = new JPanel();
		topPanel.setLayout( new BorderLayout() );
		getContentPane().add( topPanel );

		// Create a new tree control
		tree = new JTree();

		// Add the listbox to a scrolling pane
		scrollPane = new JScrollPane();
		scrollPane.getViewport().add( tree );
		topPanel.add( scrollPane, BorderLayout.CENTER );
	}

	// Main entry point for this example
	public static void main( String args[] )
	{
		// Create an instance of the test application
		TreeExample mainFrame	= new TreeExample();
		mainFrame.setVisible( true );
	}
}