Line highlighting in Text Component

Question

I'm trying to figure out how to apply a colored background to certain lines of a text component. This is common, for instance, in a lot of editors, especially IDE's (notably, Eclipse), where the currently selected line has a separate background color from the rest of the page. I'm having a lot of trouble understanding how to use Elements and Views and EditorKits and all that, and I'm not even sure if that will solve the problem. All I've been able to do so far is put a colored background behind individual characters; but then it stops at the end of the line, instead of continuing for the width of the text component.
Any help is greatly appreciated.

Answer 1

I assumed you were using the built-in Highlighter classes to do the coloring. If you aren't, you're doing a lot more work than you need to. Here's what I use:import java.awt.Color;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.text.*;
* Usage: new CurrentLineHighlighter(myColor).install(myTextComponent);
public class CurrentLineHighlighter implements ChangeListener
  static final Color DEFAULT_COLOR = new Color(0, 0, 0, 15);
  private Highlighter.HighlightPainter painter;
  private Object highlight;
  private JTextComponent comp;
  public CurrentLineHighlighter()
    this(null);
  public CurrentLineHighlighter(Color highlightColor)
    Color c = highlightColor != null ? highlightColor : DEFAULT_COLOR;
    painter = new DefaultHighlighter.DefaultHighlightPainter(c);
  public void install(JTextComponent tc)
    comp = tc;
    comp.getCaret().addChangeListener(this);
  public void stateChanged(ChangeEvent evt)
    if (highlight != null)
      comp.getHighlighter().removeHighlight(highlight);
      highlight = null;
    int pos = comp.getCaretPosition();
    Element elem = Utilities.getParagraphElement(comp, pos);
    int start = elem.getStartOffset();
    int end = elem.getEndOffset();
    try
      highlight = comp.getHighlighter().addHighlight(start, end, painter);
    catch (BadLocationException ex)
      ex.printStackTrace();
}