bufferedshapemover.java

初期JAVA学习非常有用的资料。帮助深入了解API。特别是Applet。

import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;
import java.awt.image.*;

public class BufferedShapeMover extends Applet{

	static protected Label label;

	public void init(){
		//Initialize the layout.
		setLayout(new BorderLayout());
		add(new BSMCanvas());
		label = new Label("Drag rectangle around within the area");
		add("South", label);
	}

    public static void main(String s[]) {
        Frame f = new Frame("BufferedShapeMover");
        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {System.exit(0);}
        });
	Applet applet = new BufferedShapeMover();
	f.add("Center", applet);
	applet.init();
	f.pack();
        f.setSize(new Dimension(550,250));
        f.show();
    }

}

class BSMCanvas extends Canvas implements MouseListener, MouseMotionListener{

	Rectangle rect = new Rectangle(0, 0, 100, 50);
	BufferedImage bi;
	Graphics2D big;

        // Holds the coordinates of the user's last mousePressed event.
	int last_x, last_y;
	boolean firstTime = true;
	TexturePaint fillPolka, strokePolka;
        Rectangle area;

        // True if the user pressed, dragged or released the mouse outside of the rectangle; false otherwise.
	boolean pressOut = false;		

	public BSMCanvas(){
                setBackground(Color.white);
                addMouseMotionListener(this);
                addMouseListener(this);

		// Creates the fill texture paint pattern.
                bi = new BufferedImage(5, 5, BufferedImage.TYPE_INT_RGB);
                big = bi.createGraphics();
                big.setColor(Color.pink);
                big.fillRect(0, 0, 7, 7);
                big.setColor(Color.cyan);
                big.fillOval(0, 0, 3, 3);
                Rectangle r = new Rectangle(0,0,5,5);
                fillPolka = new TexturePaint(bi, r);
		big.dispose();

		//Creates the stroke texture paint pattern.
                bi = new BufferedImage(5, 5, BufferedImage.TYPE_INT_RGB);
		big = bi.createGraphics();		
		big.setColor(Color.cyan);
                big.fillRect(0, 0, 7, 7);
                big.setColor(Color.pink);
                big.fillOval(0, 0, 3, 3);
                r = new Rectangle(0,0,5,5);
                strokePolka = new TexturePaint(bi, r);
		big.dispose();
	}

        // Handles the event of the user pressing down the mouse button.
	public void mousePressed(MouseEvent e){

		last_x = rect.x - e.getX();
		last_y = rect.y - e.getY();

                // Checks whether or not the cursor is inside of the rectangle while the user is pressing themouse.
		if(rect.contains(e.getX(), e.getY())){
			updateLocation(e);
		} else {
		BufferedShapeMover.label.setText("First position the cursor on the rectangle and then drag.");
			pressOut = true;
		}
	}

        // Handles the event of a user dragging the mouse while holding down the mouse button.
	public void mouseDragged(MouseEvent e){

		if(!pressOut){
			 updateLocation(e);
		} else {  
		BufferedShapeMover.label.setText("First position the cursor on the rectangle and then drag.");
		}
	}

        // Handles the event of a user releasing the mouse button.
	public void mouseReleased(MouseEvent e){

                // Checks whether or not the cursor is inside of the rectangle when the user releases the
		// mouse button.   
		if(rect.contains(e.getX(), e.getY())){
			updateLocation(e);
		} else {
		BufferedShapeMover.label.setText("First position the cursor on the rectangle and then drag.");
			pressOut = false;
		}
	}

	// This method required by MouseListener.
	public void mouseMoved(MouseEvent e){}

        // These methods are required by MouseMotionListener.
	public void mouseClicked(MouseEvent e){}
	public void mouseExited(MouseEvent e){}
	public void mouseEntered(MouseEvent e){}
	public void updateLocation(MouseEvent e){

		rect.setLocation(last_x + e.getX(), last_y + e.getY());
                /*
                 * Updates the label to reflect the location of the
                 * current rectangle 
                 * if checkRect returns true; otherwise, returns error message.
                 */
                if (checkRect()) {
                    BufferedShapeMover.label.setText("Rectangle located at " +
                                                     rect.getX() + ", " +
                                                     rect.getY());
                } else {
                    BufferedShapeMover.label.setText("Please don't try to "+
                                                     " drag outside the area.");
                }
		repaint();
	}

	public void paint(Graphics g){
                update(g);
	}

	public void update(Graphics g){
		Graphics2D g2 = (Graphics2D)g;
                 
          	if(firstTime){
                    Dimension dim = getSize();
                    int w = dim.width;
                    int h = dim.height;
                    area = new Rectangle(dim);
		    bi = (BufferedImage)createImage(w, h);
		    big = bi.createGraphics();
		    rect.setLocation(w/2-50, h/2-25);
		    big.setStroke(new BasicStroke(8.0f));
		    firstTime = false;
		} 

		// Clears the rectangle that was previously drawn.
		big.setColor(Color.white);
		big.clearRect(0, 0, area.width, area.height);

		// Draws and fills the newly positioned rectangle to the buffer.
		big.setPaint(strokePolka);
		big.draw(rect);
		big.setPaint(fillPolka);
		big.fill(rect);

		// Draws the buffered image to the screen.
		g2.drawImage(bi, 0, 0, this);
	}
	/*
         * Checks if the rectangle is contained within the applet window.  If the rectangle
         * is not contained withing the applet window, it is redrawn so that it is adjacent
         * to the edge of the window and just inside the window.
	 */
	boolean checkRect(){
            if (area == null) {
                return false;
            }
		if(area.contains(rect.x, rect.y, 100, 50)){
			return true;
		}
		int new_x = rect.x;
		int new_y = rect.y;

		if((rect.x+100)>area.width){
			new_x = area.width-99;
		}
		if(rect.x < 0){  
			new_x = -1;
		}
		if((rect.y+50)>area.height){
			new_y = area.height-49;
		}
		if(rect.y < 0){  
			new_y = -1;
		}
		rect.setLocation(new_x, new_y);
		return false;
	}

}