May 19

When you add a JTextField to a BoxLayout managed panel it will expand vertically to take up available space.

To avoid this you can simply set the maximum size of the field to be the same as its preferred size.

textField.setMaximumSize( textField.getPreferredSize() );

written by objects \\ tags: , ,

Feb 22

We’ve all got code riddled with System.out.println() messages. We should use a logging framework, but often we’re in a rush and we end up writing to stdout because its simpler at the time.

If there are too many System.out.println() calls and we want to stop them going to the console then we can redirect stdout and stderr to a different stream using the setOut() and setErr() methods provided by the System class.

If we want to instead have them written to a Swing text component such as a JTextArea or JTextPane then what we need is an OutputStream subclass that will write to the text component.

The following code shows how that can achieved, resulting in System.out.println() call writing to your designated JTextComponent.


import javax.swing.SwingUtilities;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.JTextComponent;

public class RedirectOutput {

	private JTextComponent textComponent;
	public static void sendTo(JTextComponent textComponent) {
		new RedirectOutput(textComponent).redirectSystemStreams();
	private RedirectOutput(JTextComponent textComponent) {
		this.textComponent = textComponent;
	private void updateTextComponent(final String text) {
		SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				Document doc = textComponent.getDocument();
				try {
					doc.insertString(doc.getLength(), text, null);
				} catch (BadLocationException e) {
					throw new RuntimeException(e);
				textComponent.setCaretPosition(doc.getLength() - 1);

	private void redirectSystemStreams() {
		OutputStream out = new OutputStream() {
			public void write(final int b) throws IOException {
				updateTextComponent(String.valueOf((char) b));

			public void write(byte[] b, int off, int len) throws IOException {
				updateTextComponent(new String(b, off, len));

			public void write(byte[] b) throws IOException {
				write(b, 0, b.length);

		System.setOut(new PrintStream(out, true));
		System.setErr(new PrintStream(out, true));


written by objects \\ tags: , , , , , , ,

Feb 26

To switch focus to a text field (or any component actually) just call the target components requestFocusInWindow() method.


NB. There is also a requestFocus() method but it’s behavior is platform dependent and thus it’s use is discouraged.

written by objects \\ tags: , ,