Abstract Class In Java :
- A class which is declared with the abstract keyword is known as an abstract class in Java. It contain the abstract and non – abstract methods (method with the body). It needs to be extended and its method implemented. It cannot be instantiated.
- All functions in java by default virtual.
Abstraction
- Abstraction is a process of hiding the implementation details and showing only functionality to the user.
- Concrete methods:Regular methods with body.
- Abstract class: Cannot create object but they can be subclasses. To access it, it must be inherited from another class. Abstract class at least one abstract method. An abstract class is a class that is declared abstract.
- Abstract classes can have contains Constructors, Member variables, Instance member and Normal methods. Constructor of the abstract class will be used to instantiate the abstract class instance variable.
- Abstract class can implement interfaces without even providing the implementation of interface methods.
- Abstract class is used to provide common method implementation to all the subclasses or to provide default implementation.
- A class cannot be both ‘abstract’ & ‘final’.
- We cannot make an inner class as abstract.
- We cannot use static method but can use static variable in the abstract class.
- If we don’t want to override abstract in its sub-class then declare that sub-class as abstract.
- Overridden abstract class methods will be accessed by its sub-class object.
- Abstract method: Only be used in an abstract class, and it does not have a body. The body is provided by the subclass.
- If you inherit an abstract class, you have to provide implementations to all the abstract methods in it.
- An abstract method has no implementation. It just has a method signature.
- Abstract method can never be final and static.
- Any subclass that extends an abstract class must implement all the abstract methods declared by the super class. All the abstract methods must be overridden.
- When you extend abstract class with abstract method, you must define the abstract method in the child class, or make the child class abstract.
- It can have final methods which will force the subclass not to change the body of the method.
For example:
- Every ATM card common functionality cash debit but password is different.
- Any person all different attributes name, age and working area.
