alienEntity.java

package org.newdawn.spaceinvaders;

/**
 * An entity which represents one of our space invader aliens.
 * 
 * @author Kevin Glass
 */
public class AlienEntity extends Entity 
{
	/** The speed at which the alient moves horizontally */
	private double moveSpeed = 75;
	/** The game in which the entity exists */
	private Game game;
	
	/**
	 * Create a new alien entity
	 * 
	 * @param game The game in which this entity is being created
	 * @param ref The sprite which should be displayed for this alien
	 * @param x The intial x location of this alien
	 * @param y The intial y location of this alient
	 */
	public AlienEntity(Game game,String ref,int x,int y) 
        {
		super(ref,x,y);
		
		this.game = game;
		dx = -moveSpeed;
	}

	/**
	 * Request that this alien moved based on time elapsed
	 * 
	 * @param delta The time that has elapsed since last move
	 */
	public void move(long delta) 
        {
		// if we have reached the left hand side of the screen and
		// are moving left then request a logic update 
		if ((dx < 0) && (x < 10)) 
                {
			game.updateLogic();
		}
		// and vice vesa, if we have reached the right hand side of 
		// the screen and are moving right, request a logic update
		if ((dx > 0) && (x > 750)) 
                {
			game.updateLogic();
		}
		
		// proceed with normal move
		super.move(delta);
	}
	
	/**
	 * Update the game logic related to aliens
	 */
	public void doLogic() 
        {
		// swap over horizontal movement and move down the
		// screen a bit
		dx = -dx;
		y += 10;
		
		// if we've reached the bottom of the screen then the player
		// dies
		if (y > 570) 
                {
			game.notifyDeath();
		}
	}
	
	/**
	 * Notification that this alien has collided with another entity
	 * 
	 * @param other The other entity
	 */
	public void collidedWith(Entity other) 
        {
		// collisions with aliens are handled elsewhere
	}
}