Why does this JTextPane cause JScrollPane to flicker when I type into it?

[Gerald Lampi]

The following code example causes the vertical scrollbar to appear and disappear as you type into the JTextPane.

Any ideas on how to fix it?

Screencast of the flicker issue.

import java.awt.EventQueue;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import java.awt.BorderLayout;
import javax.swing.JTextPane;
import javax.swing.JPanel;
import javax.swing.JLabel;
import java.awt.FlowLayout;

public class JTextPaneScrollIssue {
	private JFrame frmJscrollpanescrollissue;
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					JTextPaneScrollIssue window = new JTextPaneScrollIssue();
					window.frmJscrollpanescrollissue.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the application.
	 */
	public JTextPaneScrollIssue() {
		initialize();
	}

	/**
	 * Initialize the contents of the frame.
	 */
	private void initialize() {
		frmJscrollpanescrollissue = new JFrame();
		frmJscrollpanescrollissue.setTitle("JScrollPaneScrollIssue");
		frmJscrollpanescrollissue.setBounds(100, 100, 450, 468);
		frmJscrollpanescrollissue.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		JPanel pnMain = new JPanel();
		pnMain.setLayout(new GridLayout(14, 1, 0 , 0));
		JScrollPane scrollPane = new JScrollPane(pnMain);
		
		JPanel panel = new JPanel();
		pnMain.add(panel);
		
		JLabel lblNewLabel_1 = new JLabel("New label");
		panel.add(lblNewLabel_1);
		
		JPanel panel_1 = new JPanel();
		pnMain.add(panel_1);
		
		JLabel lblNewLabel_4 = new JLabel("New label");
		panel_1.add(lblNewLabel_4);
		
		JPanel panel_2 = new JPanel();
		pnMain.add(panel_2);
		
		JLabel lblNewLabel_5 = new JLabel("New label");
		panel_2.add(lblNewLabel_5);
		
		JPanel panel_3 = new JPanel();
		pnMain.add(panel_3);
		
		JLabel lblNewLabel_6 = new JLabel("New label");
		panel_3.add(lblNewLabel_6);
		
		JPanel panel_4 = new JPanel();
		pnMain.add(panel_4);
		
		JLabel lblNewLabel_7 = new JLabel("New label");
		panel_4.add(lblNewLabel_7);
		
		JPanel panel_5 = new JPanel();
		pnMain.add(panel_5);
		
		JLabel lblNewLabel_8 = new JLabel("New label");
		panel_5.add(lblNewLabel_8);
		
		JPanel panel_6 = new JPanel();
		pnMain.add(panel_6);
		
		JLabel lblNewLabel_9 = new JLabel("New label");
		panel_6.add(lblNewLabel_9);
		
		JPanel panel_7 = new JPanel();
		pnMain.add(panel_7);
		
		JLabel lblNewLabel_2 = new JLabel("New label");
		panel_7.add(lblNewLabel_2);
		
		JPanel panel_8 = new JPanel();
		pnMain.add(panel_8);
		
		JLabel lblNewLabel_10 = new JLabel("New label");
		panel_8.add(lblNewLabel_10);
		
		JPanel panel_9 = new JPanel();
		pnMain.add(panel_9);
		
		JLabel lblNewLabel_11 = new JLabel("New label");
		panel_9.add(lblNewLabel_11);
		
		JPanel panel_10 = new JPanel();
		pnMain.add(panel_10);
		
		JLabel lblNewLabel_12 = new JLabel("New label");
		panel_10.add(lblNewLabel_12);
		
		JPanel panel_11 = new JPanel();
		pnMain.add(panel_11);
		
		JLabel lblNewLabel_3 = new JLabel("New label");
		panel_11.add(lblNewLabel_3);
		
		JPanel panel_12 = new JPanel();
		pnMain.add(panel_12);
		
		JLabel lblNewLabel_13 = new JLabel("New label");
		panel_12.add(lblNewLabel_13);
		
		JPanel panel_13 = new JPanel();
		FlowLayout flowLayout = new FlowLayout();
		flowLayout.setVgap(0);
		flowLayout.setHgap(0);
		flowLayout.setAlignment(FlowLayout.LEFT);
		panel_13.setLayout(flowLayout);
		pnMain.add(panel_13);
		
		JLabel lblNewLabel = new JLabel("New label: ");
		panel_13.add(lblNewLabel);
		
		JTextPane txtpnTypeInHere = new JTextPane();
		txtpnTypeInHere.setText("Type in here to see the vertical scrollbar flicker. ");
		panel_13.add(txtpnTypeInHere);
		frmJscrollpanescrollissue.getContentPane().add(scrollPane, BorderLayout.CENTER);
		
	}
}

[Rob Camick]

First of all it works OK with a JTextArea.

Why the difference? I'm just guessing.

In both cases the text components have a variable preferred size. As characters are added/removed the preferred size changes and the component is revalidated.

For a text pane the text wraps automatically (when needed), for the text area it doesn't.

Maybe the text pane has a problem thinking it needs to wrap the text but then realizes it doesn't so the scrollbar flashes.

[Darryl Burke]

Gerald, we don't have too many rules here, but we do ask that you BeForthrightWhenCrossPostingToOtherSites

http://forums.oracle.com/forums/thread.jspa?threadID=2264353