LineHighlightPainter.java Source code

Introduction

Here is the source code for LineHighlightPainter.java

Source

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.Shape;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.text.BadLocationException;
import javax.swing.text.Caret;
import javax.swing.text.DefaultCaret;
import javax.swing.text.Highlighter;
import javax.swing.text.JTextComponent;

public class LineHighlightPainter implements Highlighter.HighlightPainter {

    private void paintLine(Graphics g, Rectangle r, int x2) {
        int ytop = r.y + r.height - 3;
        g.fillRect(r.x, ytop, x2 - r.x, 3);
    }

    public void paint(Graphics g, int p0, int p1, Shape bounds, JTextComponent c) {

        Rectangle r0 = null, r1 = null, rbounds = bounds.getBounds();
        int xmax = rbounds.x + rbounds.width;
        try {
            r0 = c.modelToView(p0);
            r1 = c.modelToView(p1);
        } catch (BadLocationException ex) {
            return;
        }
        if ((r0 == null) || (r1 == null))
            return;

        g.setColor(c.getSelectionColor());

        // special case if p0 and p1 are on the same line
        if (r0.y == r1.y) {
            paintLine(g, r0, r1.x);
            return;
        }

        // first line, from p1 to end-of-line
        paintLine(g, r0, xmax);

        // all the full lines in between, if any (assumes that all lines have
        // the same height--not a good assumption with JEditorPane/JTextPane)
        r0.y += r0.height; // move r0 to next line
        r0.x = rbounds.x; // move r0 to left edge
        while (r0.y < r1.y) {
            paintLine(g, r0, xmax);
            r0.y += r0.height; // move r0 to next line
        }

        // last line, from beginning-of-line to p1
        paintLine(g, r0, r1.x);
    }

    public static void main(String args[]) {

        // extend DefaultCaret as an anonymous inner class
        Caret lineHighlightPainterCaret = new DefaultCaret() {
            private Highlighter.HighlightPainter lhp = new LineHighlightPainter();

            // override getSelectionPainter to return the LineHighlightPainter
            protected Highlighter.HighlightPainter getSelectionPainter() {
                return lhp;
            }
        };

        JFrame frame = new JFrame("LineHighlightPainter demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JTextArea area = new JTextArea(9, 45);
        area.setCaret(lineHighlightPainterCaret);
        area.setLineWrap(true);
        area.setWrapStyleWord(true);
        area.setText("This is the story\nof the hare who\nlost his spectacles.");
        frame.getContentPane().add(new JScrollPane(area), BorderLayout.CENTER);
        frame.pack();
        frame.setVisible(true);
    }
}