Assignment 6: An animation of alien activity

---

• A button for creating new aliens.
• A "board" that is the aliens’ universe
• An abstract class called Alien that looks like the following:

public abstract class Alien {
    int x, y,       // location of alien
        size;       // size of alien
    Color color;    // color of alien
    final static int boardSize = 200,
                     xBoard = 50,
                     yBoard = 50;

// Constructor: initialize x and y to a random position inside the board, so that the even // the biggest alien gets drawn completely inside the board.
    public Alien()  { }
 
    // compute coordinates of next position of alien
    abstract void move();

    // draw alien at his location within the universe
    abstract void draw(Graphics g);
}

• The applet skeleton that accomplishes the animation follows:

import java.awt.*;
import java.applet.*;

public class animations extends Applet {
    int sleepTime = 80,     // time step between repaints
    // insert the other applet variables here

    // initialize applet
    public void init() {}
 
                // paint accomplishes the animation
    public void paint(Graphics g) {
       // draw the bounding box of the universe and all the aliens

        try {
            Thread.sleep(sleepTime);
        }
        catch (InterruptedException e) {
            showStatus(e.toString());
        }
        repaint();
    }

    public boolean action(Event event, Object o) {

        // process the button being clicked, then  ....
        repaint();
        return true;
    }
}

• Your abstract class Alien will have at least the 3 subclasses described below:


1. Martian:
• They are red squares, 10 pixels on a side.
• When created, they are placed randomly on the board.
• At each time step, they move randomly 5 pixels either left or right  and randomly 5 pixels either up or down.
• They stay fully within the universe at all times.  If a move would put them out of the universe, they wrap around (like a modulus operation).
2. Venutians:
• They are green ovals, 20 pixels wide and 40 pixels high.
• When created, they are placed randomly on the board, and are given a movement vector (x, y), where x is a random number of pixels between 0 and 9, inclusive; y is another number in the same interval.
• At each time step, they move according to this vector, except that when the reach a boundary, the reflect, like a billiard ball.
• They stay fully within the universe at all times.
3. Earthlings:
• They are blue circles, 6 pixels in diameter that move in a circle of radius 30 pixels.
• When they are created, the center of their circle is randomly selected within the universe.
• At each time step, they move around the circle 0.2 radians.
• If any portion of their orbit falls outside the universe, then when they are on that portion of their orbit, they are not visible.
• When the create button is clicked, you create a randomly selected alien.  Your applet should be able to hold a maximum of 20 such aliens.
• You must use polymorphism in your paint method to update the positions of the aliens and to draw them.  This is illustrated in the solar system applet presented in class.  A link to its source code appears on the course’s Resources page.
• You optionally can create other kinds of Aliens.  For example, you might create a subclass of Alien, called Jovians, who are pulled by gravity to the bottom of the universe, and bounce half as high.  Their horizontal direction is a random number of pixels between 0 and 15.  You can fill in other details.
• Here is the html file you should use:

Turn In Procedure