#48 Abstraction & Interface In Java | Abstract Class Vs. Interface | final keyword | Java Tutorials

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Abstraction in Java
In java abstract is a keyword which can only be used with:
a. Methods
b. Classes

Abstract Method:
If you want a class to contain a particular method but you want the actual implementation of that method to be determined by child classes, you can declare the method in the parent class as an abstract.
1. The abstract keyword is used to declare the method as abstract.
2. You have to place the abstract keyword before the method name in the method declaration. E.g., public void get();
3. An abstract method contains a method signature, but no method body.
4. Instead of curly braces, an abstract method will have a semicolon (;) at the end.

Declaring a method as abstract has two consequences: -
a. The class containing it must be declared as abstract.
b. Any class inheriting the current class must either override the abstract method or declare itself as abstract.

Abstract Class:
A class which contains the abstract keyword in its declaration is known as an abstract class. E.g., abstract class Employee{ }
1. Abstract classes may or may not contain abstract methods, i.e., methods without a body. . E.g., public void get();
2. But, if a class has at least one abstract method, then the class must be declared abstract.
3. If a class is declared abstract, it cannot be instantiated means we can’t create object of that class.
4. To use an abstract class, you have to inherit it from another class, and also you need to define/override all the abstract method of that class in your class.


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