shapemover.java

初期JAVA学习非常有用的资料。帮助深入了解API。特别是Applet。

/*
* @(#)ShapeMover.java   1.2 98/07/31
*/


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

/*
 * This applet allows the user to move a texture painted rectangle around the applet
 * window.  The rectangle flickers and draws slowly because this applet does not use 
 * double buffering.
*/

public class ShapeMover extends Applet{
	static protected Label label;

	public void init(){

		setLayout(new BorderLayout());
		add(new SMCanvas());

		label = new Label("Drag rectangle around within the area");
		add("South", label);
	}

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

}


class SMCanvas 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 SMCanvas(){
               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 the mouse.
			if(rect.contains(e.getX(), e.getY())) updateLocation(e);
			else {
                        	ShapeMover.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 ShapeMover.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 {
                        	ShapeMover.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){}

                // Updates the coordinates representing the location of the current rectangle.
        	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()) {
                    ShapeMover.label.setText("Rectangle located at " +
                                                     rect.getX() + ", " +
                                                     rect.getY());
                } else {
                    ShapeMover.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;
		Dimension dim = getSize();
		int w = (int)dim.getWidth();
		int h = (int)dim.getHeight();
		g2.setStroke(new BasicStroke(8.0f));

		if(firstTime){
			area = new Rectangle(dim);
			rect.setLocation(w/2-50, h/2-25);
			firstTime = false;
		}

	        // Clears the rectangle that was previously drawn.
		g2.setPaint(Color.white);
		g2.fillRect(0, 0, w, h);
			
                // Draws and fills the newly positioned rectangle.
		g2.setPaint(strokePolka);
		g2.draw(rect);
		g2.setPaint(fillPolka);
		g2.fill(rect);

	}

        /*
	 * 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.getWidth()){
                        new_x = (int)area.getWidth()-99;
                }
                if(rect.x < 0){
                        new_x = -1;
                }
                if((rect.y+50)>area.getHeight()){
                        new_y = (int)area.getHeight()-49;
                }
                if(rect.y < 0){
                        new_y = -1;
                }
                rect.setLocation(new_x, new_y);
                return false;  
		}
}