Added class hierarchies.

double-dispatch/src/main/java/com/iluwatar/Asteroid.java

@@ -0,0 +1,8 @@
+package com.iluwatar;
+
+public class Asteroid extends Meteoroid {
+
+	public Asteroid(int left, int top, int right, int bottom) {
+		super(left, top, right, bottom);
+	}
+}

double-dispatch/src/main/java/com/iluwatar/GameObject.java

@@ -0,0 +1,13 @@
+package com.iluwatar;
+
+public abstract class GameObject extends Rectangle {
+	
+	public GameObject(int left, int top, int right, int bottom) {
+		super(left, top, right, bottom);
+	}
+	
+	@Override
+	public String toString() {
+		return this.getClass().getSimpleName();
+	}
+}

double-dispatch/src/main/java/com/iluwatar/Meteoroid.java

@@ -0,0 +1,8 @@
+package com.iluwatar;
+
+public class Meteoroid extends GameObject {
+
+	public Meteoroid(int left, int top, int right, int bottom) {
+		super(left, top, right, bottom);
+	}
+}

double-dispatch/src/main/java/com/iluwatar/Rectangle.java

@@ -0,0 +1,33 @@
+package com.iluwatar;
+
+public class Rectangle {
+
+	private int left;
+	private int top;
+	private int right;
+	private int bottom;
+
+	public Rectangle(int left, int top, int right, int bottom) {
+		this.left = left;
+		this.top = top;
+		this.right = right;
+		this.bottom = bottom;
+	}
+	
+	public int getLeft() {
+		return left;
+	}
+	public int getTop() {
+		return top;
+	}
+	public int getRight() {
+		return right;
+	}
+	public int getBottom() {
+		return bottom;
+	}	
+	
+	boolean intersectsWith(Rectangle r) {
+		return !(r.getLeft() > getRight() || r.getRight() < getLeft() || r.getTop() > getBottom() || r.getBottom() < getTop());
+	}
+}

double-dispatch/src/main/java/com/iluwatar/SpaceStationIss.java

@@ -0,0 +1,8 @@
+package com.iluwatar;
+
+public class SpaceStationIss extends SpaceStationMir {
+
+	public SpaceStationIss(int left, int top, int right, int bottom) {
+		super(left, top, right, bottom);
+	}
+}

double-dispatch/src/main/java/com/iluwatar/SpaceStationMir.java

@@ -0,0 +1,8 @@
+package com.iluwatar;
+
+public class SpaceStationMir extends GameObject {
+
+	public SpaceStationMir(int left, int top, int right, int bottom) {
+		super(left, top, right, bottom);
+	}
+}