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Inheritance in Java

Inheritance can be defined as the process where one class acquires the properties (methods and fields) of another. In other words, the derived class inherits the states and behaviors from the base class. The derived class is also called subclass and the base class is also known as super-class. The derived class can add its own additional variables and methods. These additional variable and methods differentiates the derived class from the base class.

Inheritance is a compile-time mechanism. A super-class can have any number of subclasses. But a subclass can have only one superclass. This is because Java does not support multiple inheritance.

The superclass and subclass have “is-a” relationship between them. Let’s have a look at the syntex below.

The extends keyword indicates that you are making a new class that derives from an existing class.

In the terminology of Java, a class that is inherited is called a super class. The new class is called a subclass.

Here is the complete example:

Types of inheritance in java

On the basis of class, there can be three types of inheritance in java: single, multilevel and hierarchical.

In java programming, multiple and hybrid inheritance is supported through interface only. We will learn about interfaces later.



Constructors and Inheritance

The constructor in the superclass is responsible for building the object of the superclass and the constructor of the subclass builds the object of subclass. When the subclass constructor is called during object creation, it by default invokes the default constructor of super-class. Hence, in inheritance the objects are constructed top-down. The super class constructor can be called explicitly using the keyword super, but it should be first statement in a constructor. The keyword super always refers to the superclass immediately above of the calling class in the hierarchy. The use of multiple super keywords to access an ancestor class other than the direct parent is illegal.



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