drawinggizmo.java

Java程序设计(美) David D. Riley著 机械工业出版社 书籍配套 代码

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

/**  DrawingGizmo is like a drawing pen that
 *  can be moved around a drawing canvas
 *  This is similar to a turtle from the
 *  LOGO programming language.
 *
 *  Class Invariant
 *      window is instantiated with a canvas of 260 by 160 colored
 *      and  the window is colored as established by setBackground
 *		and  (locX, locY) maintains the position of the drawing tool
 *			 within the window canvas
 *      and  direction indicates the direction of travel (in degrees)
 *          (increasing the direction value rotates clockwise) 
 */
public class DrawingGizmo extends JComponent {
    private static JFrame window;
    private int locX, locY;
    private boolean isDrawing;
    private int direction;
    private Robot delayTimer;

    /** post:   window@pre!=null implies window == window@pre
	 *			and  window.getContentPane().getWidth()==200  and  window.getContentPane().getHeight()==160
	 *			and  getX() == 127  and  getY() == 77  and  getWidth() == getHeight() == 9
	 *			and  isDrawing
	 *			and  direction == -90 (the triangle points up)
	 *			and  getForeground() == Color.green 
     */
    public DrawingGizmo()  {
        super();
        if  ( window == null )   {
            window = new JFrame( "Drawing Canvas");
			window.getContentPane().setLayout(null);
			window.setVisible(true);
            window.setBounds(50, 50, 
                            260 + window.getInsets().left + window.getInsets().right,
                            160 + window.getInsets().top + window.getInsets().bottom); 
        }
		locX = 127;
		locY = 77;
		setBounds(locX,locY,9,9);
        draw();
        direction = -90;
        window.getContentPane().add(this);
        repaint();
        window.repaint();
        try {
            delayTimer = new Robot();
        }
        catch (Exception e) {
            System.out.println("This System does not support java.awt.Robot usage.");
        }
    }

    /** post:  isDrawing */
    public void draw()   {
        isDrawing = true;
    }

    /** post:   !isDrawing */
    public void dontDraw()   {
        isDrawing = false;
        repaint();
    }

    /** post:  direction == direction@pre + d  (direction rotates clockwise by d degrees) */
    public void turnBy(int d)   {
        direction = direction + d;
        repaint();
    }

    /** post:  direction == direction@pre + 30  (direction rotates clockwise by 10 degrees) */
    public void turnClockwise()   {
        turnBy(30);
    }

    /** post:  direction == direction@pre - 30  (direction rotates counterclockwise by 10 degrees) */
    public void turnCounterclockwise()   {
        turnBy(-30);
    }

    /** post:  (locX, locY) is a point at angle direction and d units from (locX@pre, locY@pre)
	 *			and  isDrawing implies a line segment is drawn connecting (locX@pre, locY@pre)
	 *				 with (locX, locY) 
     */
    public void moveBy( int d )   {
        Line line;
        int oldX = locX;
        int oldY = locY;
        locX = oldX + (int)(d * Math.cos(Math.toRadians(direction)));
        locY = oldY + (int)(d * Math.sin(Math.toRadians(direction)));
        setLocation(locX,locY);
        if  ( isDrawing )   {
            line = new Line(oldX+4, oldY+4, locX+4, locY+4);
			line.setForeground(getForeground());
            window.getContentPane().add(line);
            line.repaint();
        }
        repaint();
    }

    /** post:  (locX, locY) is a point at angle direction and 20 units from (locX@pre, locY@pre)
	 *			and  isDrawing implies a line segment is drawn connecting (locX@pre, locY@pre)
	 *				 with (locX, locY) 
     */
    public void moveForward()   {
        moveBy(20);
    }
    
    /** post:  the window is recolored to match c */
    public void setBackground(Color c)   {
        window.setBackground(c);
    }

    /**   post: thisis drawn as an arrow at position (locX,locY), 
     *              angled according to direction
	 *          and isDrawing implies the arrow is colored green
	 *			otherwise the arrow is colored red 
     */
    public void paint(Graphics g)  {
		if (isDrawing)
			g.setColor( Color.green );
		else
			g.setColor( Color.red );
        ((Graphics2D)g).rotate(Math.toRadians(direction), getWidth()/2, getHeight()/2);
        g.drawLine(2, 1, 8, 4);
        g.drawLine(8, 4, 2, 7);
        g.drawLine(0, 4, 8, 4);
        g.drawLine(6, 3, 6, 5);
        g.drawLine(5, 3, 5, 5);
        g.drawLine(4, 2, 4, 6);
        g.drawLine(3, 2, 3, 6);
    }
   
    public void delay2Sec() {
        delayTimer.delay(2000);
    }
   
    public void delayBy(int t) {
        delayTimer.delay(t);
    }
   
/** This internal class is used to construct line segments for the drawing tool. */   
private class Line extends JComponent  {
    private boolean isMajorDiagonal;
    public Line(int x1, int y1, int x2, int y2) {
        super();
        setBounds(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x1-x2)+1, Math.abs(y1-y2)+1);
        isMajorDiagonal = (x1==Math.min(x1,x2) && y1==Math.min(y1,y2)) || (x2==Math.min(x1,x2) && y2==Math.min(y1,y2));         
    }
    
    public void paint(Graphics g) {
        g.setColor(getForeground());
        if (isMajorDiagonal)
            g.drawLine(0, 0, getWidth()-1, getHeight()-1);
        else
            g.drawLine(0, getHeight()-1, getWidth()-1, 0);
    }
}

}