Refactor to support multiple balls

core/src/com/me/brickbuster/BrickBuster.java

@@ -27,20 +27,20 @@ public class BrickBuster extends ApplicationAdapter {
 	private BitmapFont font;
 	private SpriteBatch batch;
 
-	private Ball ball;
 	private Paddle paddle;
+	private ArrayList<Ball> balls;
 	private ArrayList<Brick> bricks;
 	private ArrayList<PowerUp> powerUps;
-	private boolean playing = false;
 
 	@Override
 	public void create () {
 		font = new BitmapFont();
 		batch = new SpriteBatch();
 
-		ball = new Ball(this);
 		paddle = new Paddle(this);
+
 		powerUps = new ArrayList<PowerUp>();
+
 		bricks = new ArrayList<Brick>();
 		for (int col = 0; col < 13; col++) {
 			for (int row = 0; row < 7; row++) {
@@ -56,6 +56,9 @@ public class BrickBuster extends ApplicationAdapter {
 				bricks.add(new Brick(this, powerUpType, x, HEIGHT - y));
 			}
 		}
+
+		balls = new ArrayList<Ball>();
+		balls.add(new Ball(this));
 	}
 
 	@Override
@@ -74,7 +77,9 @@ public class BrickBuster extends ApplicationAdapter {
 		for (PowerUp powerUp : powerUps) {
 			powerUp.render();
 		}
+		for (Ball ball : balls) {
 			ball.render();
+		}
 		paddle.render();
 		long finish_render = System.nanoTime() - start_render;
 
@@ -86,13 +91,19 @@ public class BrickBuster extends ApplicationAdapter {
 	}
 
 	public void update(float dt) {
-		if (Gdx.input.justTouched() && (!isPlaying() || ball.isStuck())) {
+		for (Iterator<Ball> it = balls.iterator(); it.hasNext();) {
-			playing = true;
+			Ball ball = it.next();
-			ball.launch();
-		}
 			ball.update(dt);
-		paddle.update(dt);
+			if (ball.isDead()) {
+				it.remove();
+			}
+		}
 
+		if (balls.isEmpty()) {
+			reset();
+		}
+
+		paddle.update(dt);
 
 		for (Iterator<PowerUp> it = powerUps.iterator(); it.hasNext();) {
 			PowerUp powerUp = it.next();
@@ -104,24 +115,25 @@ public class BrickBuster extends ApplicationAdapter {
 
 		if (getBricks().isEmpty()) {
 			create();
-			playing = false;
 		}
 	}
 
+	public void reset() {
+		Paddle paddle = getPaddle();
+		Ball ball = new Ball(this);
+		ball.setX(paddle.getX());
+		ball.setY(Paddle.PADDLE_Y + Paddle.PADDLE_HEIGHT + Ball.RADIUS);
+		balls.add(ball);
+		paddle.setSticky(false);
+		paddle.setWidth(Paddle.DEFAULT_WIDTH);
+	}
+
 	@Override
 	public void dispose () {
 	}
 
-	public boolean isPlaying() {
+	public ArrayList<Ball> getBalls() {
-		return playing;
+		return balls;
-	}
-
-	public void setPlaying(boolean playing) {
-		this.playing = playing;
-	}
-
-	public Ball getBall() {
-		return ball;
 	}
 
 	public Paddle getPaddle() {

core/src/com/me/brickbuster/entity/Ball.java

@@ -1,5 +1,6 @@
 package com.me.brickbuster.entity;
 
+import com.badlogic.gdx.Gdx;
 import com.badlogic.gdx.graphics.Color;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
 import com.badlogic.gdx.math.MathUtils;
@@ -20,10 +21,12 @@ public class Ball extends Entity {
 
 	public Vector2 direction;
 	private float speed;
-	private boolean isStuck = false;
+	private boolean isStuck = true;
+	private boolean isDead = false;
 
 	public Ball(BrickBuster brickBuster) {
 		super(brickBuster,BrickBuster.WIDTH/2, Paddle.PADDLE_Y + Paddle.PADDLE_HEIGHT + RADIUS);
+		this.speed = getBrickBuster().getBricks().size() > BLOCKS_FOR_BOOST? DEFAULT_SPEED : DEFAULT_SPEED;
 	}
 
 	@Override
@@ -36,9 +39,13 @@ public class Ball extends Entity {
 
 	@Override
 	public void update(float dt) {
-		if (!getBrickBuster().isPlaying() || isStuck()) {
+		if (isStuck || isDead) {
+			if (!isDead && Gdx.input.justTouched()) {
+				launch();
+			} else {
 				return;
 			}
+		}
 
 		Vector2 new_pos = getPos().cpy().add(direction.cpy().scl(speed * dt));
 
@@ -71,7 +78,7 @@ public class Ball extends Entity {
 		} else if (new_pos.y + RADIUS > BrickBuster.HEIGHT) {
 			Utils.reflect(direction, BrickBuster.HORIZONTAL_EDGE);
 		} else if (new_pos.y - RADIUS < 0) {
-			reset();
+			isDead = true;
 			return;
 		}
 
@@ -101,13 +108,12 @@ public class Ball extends Entity {
 	public void launch() {
 		if (getBrickBuster().getPaddle().isSticky()) {
 			direction = paddleReflectAngle();
-			isStuck = false;
 		} else {
 			// launch at random angle between 135 and 45 degrees
 			float angle = MathUtils.random(MathUtils.PI/2) + MathUtils.PI/4;
 			direction = new Vector2(MathUtils.cos(angle), MathUtils.sin(angle));
-			speed = DEFAULT_SPEED;
 		}
+		isStuck = false;
 	}
 
 	public void paddleCollision() {
@@ -120,17 +126,12 @@ public class Ball extends Entity {
 		direction = paddleReflectAngle();
 	}
 
-	public void reset() {
-		Paddle paddle = getBrickBuster().getPaddle();
-		setX(paddle.getX());
-		setY(Paddle.PADDLE_Y + Paddle.PADDLE_HEIGHT + RADIUS);
-		paddle.setSticky(false);
-		paddle.setWidth(Paddle.DEFAULT_WIDTH);
-		getBrickBuster().setPlaying(false);
-	}
 
 	public boolean isStuck() {
 		return isStuck;
 	}
 
+	public boolean isDead() {
+		return isDead;
+	}
 }

core/src/com/me/brickbuster/entity/Paddle.java

@@ -33,28 +33,33 @@ public class Paddle extends Entity {
 
 	@Override
 	public void update(float dt) {
-		Ball ball = getBrickBuster().getBall();
 		if (Gdx.input.isKeyPressed(Input.Keys.LEFT)) {
 			if (getX() - width/2 - PADDLE_SPEED * dt < 0) {
 				setX(width/2);
 				return;
 			}
 			setX(getX() - PADDLE_SPEED * dt);
-			if (!getBrickBuster().isPlaying() || ball.isStuck()) {
+
+			for (Ball ball : getBrickBuster().getBalls()) {
+				if (ball.isStuck()) {
 					ball.setX(ball.getX() - PADDLE_SPEED * dt);
 				}
 			}
+		}
 		if (Gdx.input.isKeyPressed(Input.Keys.RIGHT)) {
 			if (getX() + width/2 + PADDLE_SPEED * dt > BrickBuster.WIDTH) {
 				setX(BrickBuster.WIDTH - width/2);
 				return;
 			}
 			setX(getX() + PADDLE_SPEED * dt);
-			if (!getBrickBuster().isPlaying() || ball.isStuck()) {
+
+			for (Ball ball : getBrickBuster().getBalls()) {
+				if (ball.isStuck()) {
 					ball.setX(ball.getX() + PADDLE_SPEED * dt);
 				}
 			}
 		}
+	}
 
 	public Pair<Vector2, Vector2> getTopEdge() {
 		return new Pair<Vector2, Vector2>(