Ball.java

package testGame;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.util.Random;

class Ball extends Rectangle{

    double xVel, yVel;

    Ball() {
        x = Game.SCREEN_WIDTH  / 2;
        y = Game.SCREEN_HEIGHT / 2;
        width = height = 30;
        Random rndm = new Random();

        while (xVel != 0 || yVel != 0) {
            if (rndm.nextBoolean()) {
                xVel = rndm.nextInt(4) + 1;
                yVel = rndm.nextInt(4) + 1;
            } else {
                xVel = -rndm.nextInt(4) + 1;
                yVel = -rndm.nextInt(4) + 1;
            }
        }
        //DEBUG: set a starting speed
        xVel = yVel = -1.5;
    }

    void draw(Graphics g) {
        g.setColor(Color.white);
        g.fillOval(x, y, width, height);
    }

    void move() {

        //move the ball before checking for collisions
        x += xVel;
        y += yVel;

        bounceOffWalls(); //top and bottom
        // <-- add some sort of method to see if the ball hits the left or right walls

    }

    void bounceOffWalls() {
        //bounce off top wall
        if (y < 0 && yVel < 0) {
            y=0;
            yVel = -yVel;
        }
        //bounce off bottom wall
        if (y+height > Game.SCREEN_HEIGHT && yVel > 0) {
            y = Game.SCREEN_HEIGHT - height;
            yVel = -yVel;
        }
    }

    void checkPlayerCollision(Paddle player) {
        //Since they are both rectangles, we can check for collisions this way
        //but we only want the collision to happen if it's coming from the right side
        if (player.intersects(this) && this.xVel < 0) {
            //undo the last move of the ball to get it out of the paddle
            x -= xVel;
            y -= yVel;
            //now change the x velocity to the opposite sign.
            //Since the paddle is long and thin, this should suffice.
            this.xVel = -xVel;
        }
    }

}