Java Abstraction

Abstract class is a class that is declared abstract
*  it may or may not include abstract methods.
*  Abstract classes cannot be instantiated, but they can be subclassed.
*  If a class includes abstract methods, the class itself must be declared abstract.
* When an abstract class is subclassed, the subclass must have implementations for all of the 
   abstract  methods.
* When an abstract class inherited from an abstract class there is no need to 
  implement its super abstract methods

Abstract method is a method that is declared without an implementation:(without braces, and followed by a semicolon)
abstract void setUserName(String name);