cornercaret.java

java swing 开发代码

// CornerCaret.java
// A custom caret class.
//
package	jswing.ch21;

import javax.swing.*;
import javax.swing.text.*;
import java.awt.*;

public class CornerCaret extends DefaultCaret {

  public CornerCaret() {
    setBlinkRate(500); // half a second
  }

  protected synchronized void damage(Rectangle r) {
    if (r == null) return;
    // give values to x,y,width,height (inherited from java.awt.Rectangle)
    x = r.x; 
    y = r.y + (r.height * 4 / 5 - 3);
    width = 5;
    height = 5;
    repaint(); // calls getComponent().repaint(x, y, width, height)
  }

  public void paint(Graphics g) {
    JTextComponent comp = getComponent();
    if (comp == null) return;

    int dot = getDot();
    Rectangle r = null;
    try {
      r = comp.modelToView(dot);
    } catch (BadLocationException e) { return; }
    if (r == null) return;

    int dist = r.height * 4 / 5 - 3; // will be distance from r.y to top

    if ( (x != r.x) || (y != r.y + dist) ) {
      // paint() has been called directly, without a previous call to
      // damage(), so do some cleanup. (This happens, for example, when the
      // text component is resized.)
      repaint(); // erase previous location of caret
      x = r.x; // set new values for x,y,width,height
      y = r.y + dist;
      width = 5;
      height = 5;
    }

    if ( isVisible() ) {
      g.setColor(comp.getCaretColor());
      g.drawLine(r.x, r.y + dist, r.x, r.y + dist + 4);  // 5 vertical pixels
      g.drawLine(r.x, r.y + dist + 4, r.x + 4, r.y + dist + 4); // 5 horiz px
    }
  }

  public static void main(String args[]) {
    JFrame frame = new JFrame("CornerCaret demo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JTextArea area = new JTextArea(8, 32);
    area.setCaret(new CornerCaret());
    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);
  }
}