fallingobject.java~

书籍"Java_面向事件编程"的附带光盘代码

import objectdraw.ActiveObject;
import objectdraw.Drawable2DInterface;

// FallingObject class to encapsulate the behavior of ActiveObjects that
// fall until they reach a certain y-position then disappear
//
// Version with a hitBottom method that can easily be overridden
//
// Jim Teresco, April 2002
//

public class FallingObject extends ActiveObject {
    
    protected static final int DELAY_TIME = 33;
    
    // Fall until we get to this position
    protected int fallToPos;
    
    // how fast?
    protected double ySpeed;
    
    // what is falling?
    protected Drawable2DInterface object;
    
    // Constructor
    // Parameters: thePos - how far down the object should fall
    //             theSpeed - how far to fall each time around
    public FallingObject(int thePos, double theSpeed) {
        
        ySpeed = theSpeed;
        fallToPos = thePos;
        
        // note that it is the responsibility of the derived class
        // to call start();
    }
    
    // The run method
    public void run() {
        
        while (object.getY() < fallToPos) {
            
            pause(DELAY_TIME);
            object.move(0, ySpeed);
        }
        hitBottom();
    }
    
    // default "hit bottom" behavior - may be overridden
    protected void hitBottom() {
        
        object.removeFromCanvas();
    }
}