robot.java

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

/*	Robot objects display an image like a robot and move about a test range.
    Author:  David Riley -- Jan, 2005 */
    
/** class invariant: (direction == down  or  direction == up
 *                      or direction == left  or  direction == right)
 *                  and  0 <= column <= 11
 *                  and  0 <= row <= 8  
 */
    
import java.awt.Toolkit.*;
import java.awt.*;
import javax.imageio.ImageIO;
import java.io.*;
import javax.swing.*;
import java.awt.event.*;

public class Robot extends JComponent implements java.awt.image.ImageObserver, ActionListener {
	private java.awt.Image content;
    private RoadCourse theCourse;
    private final int up = 0;
    private final int right = 1;
    private final int down = 2;
    private final int left = 3;
    private int direction;
    private int column, row;
    private Timer clock;
    private int xDelta, yDelta, tickCount;

	/**	pre:    a proper JPEG image file must be in file /graphics/RoboDown.jpg in the
     *          same folder as the current .class file
     *  post:   an pylon image is instantiated
     *          and  getX() == 0   and  getY() == 0   
     *          and  getWidth() == 72  AND  getHeight() == 72
     *          and  direction == right
     *          and  column == 0 (leftmost column on test range)
     *          and  row == 0 (top rown on test range) 
     *          and  theCourse == rc 
     */
	public Robot(RoadCourse rc)  {
		super();
		setBounds(0, 0, 144, 144);
        setImage("graphics/RoboRight.jpg");
        direction = right;
        column = 0;
        row = 0;
        theCourse = rc;
        clock = new Timer(40, this);
	} 

	/**	post:   Upon repaint the image displayed will be given by the 
     *          file with complete pathname specified as s 
     *          (Note that the file should be a gif or jpeg encoding.)  
     */
	private void setImage(String s)  {
        java.net.URL url = getClass().getResource(s);  // for applets
        if (url == null)   {
            url = getClass().getResource("/"+s);
            if (url == null)
                try {  // for applications
                    content = ImageIO.read(new File(s));
                    System.out.println("hereh");
                } catch(IOException ioe) {
                    ioe.printStackTrace();
                }
            else
                content = getToolkit().getImage(url);
        } else
            content = getToolkit().getImage(url);

	}
    
    /** post:   direction is changed to represent a 90 degree clockwise turn */
    public void rotateClockwise() {
        direction = (direction + 1) % 4;
        if (direction == up)
            setImage("graphics/RoboUp.jpg");
        else if (direction == right)
            setImage("graphics/RoboRight.jpg");
        else if (direction == down)
            setImage("graphics/RoboDown.jpg");
        else if (direction == left)
            setImage("graphics/RoboLeft.jpg");
        repaint();
    }
    
    /** post:   canStep()@pre implies the robot steps forward one unit */
    public void moveByOneStep() {
        if (canStep()) {
            tickCount = 0;
            if (direction == up) {
                theCourse.moveRobotFromTo(row, column, row-1, column);
                row--;
                xDelta = 0;
                yDelta = -1;
                clock.start();
            } else if (direction == right) {
                theCourse.moveRobotFromTo(row, column, row, column+1);
                column++;
                xDelta = 1;
                yDelta = 0;
                clock.start();
            } else if (direction == down) {
                theCourse.moveRobotFromTo(row, column, row+1, column);
                row++;
                xDelta = 0;
                yDelta = 1;
                clock.start();
            } else if (direction == left) {
                theCourse.moveRobotFromTo(row, column, row, column-1);
                column--;
                xDelta = -1;
                yDelta = 0;
                clock.start();
            }
        }
    }

    /** post:   result == the robot can step forward in the current direction */
    private boolean canStep() {
        return (direction == up  &&  theCourse.canMoveUp(row,column))
                || (direction == right  &&  theCourse.canMoveRight(row,column))
                || (direction == down  &&  theCourse.canMoveDown(row,column)) 
                || (direction == left  &&  theCourse.canMoveLeft(row,column));
    }
    
	public void paint(Graphics g)  {
		g.drawImage(content, 0, 0, getWidth(), getHeight(), this);
	} 
    
    public void actionPerformed(ActionEvent e) {
        setLocation(getX()+xDelta, getY()+yDelta);
        repaint();
        tickCount++;
        if (tickCount == 72)
            clock.stop();
    }

}