The Java Developers Almanac 1.4

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e1006. Highlighting Words in a JTextComponent

This example demonstrates how to highlight a range of characters in a text component using highlights. The example uses a text component's highlighter to create and manage the highlights. Since one of the highlights in the highlighter is the selection, we must be careful when removing highlights not to remove the selection.

The way in which we identify our highlights is to create the highlight using a private painter. So when removing highlights from the highlighter, we remove only the ones whose painter is an instance of the private painter.

If many different highlight styles are required, it is necessary to use styles with a JTextPane. See e1007 Setting the Font and Color of Text in a JTextPane Using Styles for more details.

    JTextArea textComp = new JTextArea();
    
    // Highlight the occurrences of the word "public"
    highlight(textComp, "public");
    
    // Creates highlights around all occurrences of pattern in textComp
    public void highlight(JTextComponent textComp, String pattern) {
        // First remove all old highlights
        removeHighlights(textComp);
    
        try {
            Highlighter hilite = textComp.getHighlighter();
            Document doc = textComp.getDocument();
            String text = doc.getText(0, doc.getLength());
            int pos = 0;
    
            // Search for pattern
            while ((pos = text.indexOf(pattern, pos)) >= 0) {
                // Create highlighter using private painter and apply around pattern
                hilite.addHighlight(pos, pos+pattern.length(), myHighlightPainter);
                pos += pattern.length();
            }
        } catch (BadLocationException e) {
        }
    }
    
    // Removes only our private highlights
    public void removeHighlights(JTextComponent textComp) {
        Highlighter hilite = textComp.getHighlighter();
        Highlighter.Highlight[] hilites = hilite.getHighlights();
    
        for (int i=0; i<hilites.length; i++) {
            if (hilites[i].getPainter() instanceof MyHighlightPainter) {
                hilite.removeHighlight(hilites[i]);
            }
        }
    }
    
    // An instance of the private subclass of the default highlight painter
    Highlighter.HighlightPainter myHighlightPainter = new MyHighlightPainter(Color.red);
    
    // A private subclass of the default highlight painter
    class MyHighlightPainter extends DefaultHighlighter.DefaultHighlightPainter {
        public MyHighlightPainter(Color color) {
            super(color);
        }
    }