What is Inheritance in Java and How to Implement It?

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Introduction

Inheritance in Java is a process by which one object obtains all the properties and behaviors of its parent. It is an essential element of OOPs (object-oriented programming systems). The concept behind Inheritance in Java is that you can form new classes that are created upon existing classes. When you inherit from an existing class, you can reuse methods and domains from the parent class. Moreover, you can add new methods and fields to your existing class as well. Inheritance in Java symbolizes the IS-A relationship, which is also understood as a parent-child relationship. The new class that is built is known as a subclass (child or derived class), and the current class from which the child class is derived is known as a superclass (parent or base class).

Why is Inheritance used in Java?

The most essential use of inheritance in Java is code reusability. The derived class can access all the functionality when a derived class inherits the base class, and the base class's code can be reused in the derived class. The code can be directly used by the child class that is present in the parent class. Method overriding is also called runtime polymorphism. Inheritance permits programmers to form classes that are created upon existing classes, determine a new implementation while preserving the same behaviors, reuse code, and unassisted expand original software through public classes and interfaces.

A few necessary vocabularies associated with the concept of Inheritance in Java are:-

• Class: It is described as a set of objects sharing familiar properties.
• Subclass: Subclass also called a derived or extended class, features are inherited by this class from another class. Also, along with the inherited domains and approaches, the class developed from the actual class can add fields and methods of its own.
• Superclass: The superclass illustrates the class whose characteristics are inherited by a subclass.
• Reusability: The reusability technique enables the user to create a new class that contains the fields or methods of an existing one. It allows reusing the code. 

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Types of Inheritance in Java

The different Types of Inheritance observed in Java are:-

1. Single-Level Inheritance
2. Multi-Level Inheritance
3. Hierarchical Inheritance
4. Multiple Inheritance
5. Hybrid Inheritance

1. Single-Level Inheritance

This type of inheritance emerges for only one class, as the name suggests. Parent class has only one child class. In this type of inheritance, the characteristics are derived from a single-parent class. Because the characteristics are derived from a single base class, code reusability and the addition of new attributes are facilitated.

2. Multi-Level Inheritance

The multi-level inheritance contains the involvement of at least two or more classes. One class inherits the attributes from a parent class, and the newly formed sub-class evolves the base class for another new class. As the name suggests, multiple base classes are concerned with multi-level inheritance. In the multilevel inheritance in Java, the inherited characteristics are also from the multiple base classes, as the new derived class from the parent class becomes the base class for another recently derived class.

3. Hierarchical Inheritance

The type of inheritance in Java where a single class is inherited from many subclasses is known as Hierarchical Inheritance. Hierarchical Inheritance is a mixture of more than one type of inheritance. It is different from the multilevel inheritance, as the multiple classes are derived from one superclass. These newly derived classes inherit the attributes, approaches, etc, from this one superclass. This technique enables the reusability of a code and dynamic polymorphism (method overriding). 

4. Multiple Inheritance

Multiple inheritances is a type of inheritance where a subclass can inherit traits from more than one parent class. Multiple inheritances should not be mistaken for a multi-level inheritance, in multiple inheritances the recently derived class can hold more than one superclass. And this just derived class can inherit the attributes from these superclasses it has inherited, so there are no limitations. In java, multiple inheritances can be obtained via interfaces.

5. Hybrid Inheritance

Hybrid inheritance is a mixture of more than two types of inheritance—single and multiple. It can be obtained only via interfaces, as multiple inheritances are not used in Java. It is the assortment of simple, multiple, and hierarchical inheritances.

Why are Multiple Inheritances not supported in Java?

To decrease the complexity and simplify the language, multiple inheritances are not used in Java. Consider a design where A, B, and C are three classes. The C class inherits the A and B classes. If the A and B classes have the exact form and you name it from the child class object, there will be vagueness about whether to name the method A or B. Since compile-time errors are more useful than runtime errors, Java generates compile-time errors if you inherit two classes. So whether you have the exact method or a different one, there will be a compile-time error.

Conclusion

With the different types of inheritance in Java, the leading goal is to make sub-classes that have features inherited from the superclasses.

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