Added some contents in Abstract readme

Author: bigyaa

Interface and Abstract Class/readme.md

@@ -3,8 +3,12 @@
 * Interface basically has two main components
     - Constants (By default)
     - Methods (They do not have data type)
-* When we implement the **Interface** to a class then we nedd to define all the **methods** of the Interface.
+* When we implement the **Interface** to a class then we need to define all the **methods** of the Interface.
 
 # Abstract
-* Abstract is similar to Interface. It is a class itself. 
+* It is any class having one or more abstract methods.
+* Abstract is similar to Interface. The difference: Not all methods need to be over-ridden; common methods can be defined within the Abstract class itself.
+* Objects of Abstract classes cannot be made. It can only be inherited.
+* If one or more method is declared abstract, its class must also be abstract.
 * When we extend an Abstract Class to a Class, we need to define all the **methods** defined in the Abstract Class else the derived class again should be Abstract. 
+* It can have final methods i.e. methods that cannot be over-ridden.