چند نکته در مورد Abstract class در جاوا

• Abstract class contains zero or more abstract methods.
• the class that want to provide the definition of the abstract method present in abstract class, has to extend the abstract class.
• the abstract keyword can be used only before a method and before a class.
• we can create reference variable of the abstract class but we can not create
  an object of the abstract class using "new" keyword. it is possible using the
  concept of sub class and super class.
• abstract methods by default are public and no need for public word.