The abstract modifier, for creating abstract classes and methods
An abstract class can never be instantiated.
If a class is declared as abstract then the main purpose is for the class to be extended.
An abstract method is a method declared with out any implementation.
Any class that extends an abstract class must implement all the abstract methods of the super class unless the
subclass is also an abstract class.
If a class contains one or more abstract methods then the class need to be declared abstract.
An abstract class does not need to contain abstract methods.
Note: An abstract method need to be end with semicolon(;)
public abstract class SuperClass
abstract void method(); //abstract method
class SubClass extends SuperClass
void method() // implements the abstract method