Added inheritance and overwrite examples

typescript.html.markdown

@@ -83,8 +83,10 @@ class Point {
   //Properties
 	x: number;
 	
-	//Constructor - the public keyword is a shortcut to generate the code for a property and it's initialization, equivalent to "x" in this case
+	//Constructor - the public/private keywords are shortcuts to generate the code for a property and its initialization
-	constructor(x: number, public y: number) {
+	//Equivalent to "x" in this case
+	//Default values are also supported
+	constructor(x: number, public y: number = 0) {
 		this.x = x;
 	}
 	
@@ -95,7 +97,23 @@ class Point {
 	static origin = new Point(0, 0);
 }
 
-var p = new Point(10 ,20);
+var p1 = new Point(10 ,20);
+var p2 = new Point(25); //y will be 0
+
+//Inheritance
+class Point3D extends Point {
+	constructor(x: number, y: number, public z: number = 0) {
+		super(x, y); //Explicit call to the super class constructor is mandatory
+	}
+	
+	/Overwrite
+	dist() {
+		var d = super.dist();
+		return Math.sqrt(d * d + this.z * this.z);
+	}
+}
+
+//Modules
 
 //Generics