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Types of Inheritance in Java: Single, Multiple, Multilevel & Hybrid

Introduction

Inheritance is a critical feature in which one object acquires the properties of the parent class. It is a crucial aspect of  OOPs (Object Oriented programming systems). Before understanding inheritance, let’s briefly understand Java. Inheritance in Java is the core feature of object-oriented programming. It facilitates a derived class to inherit the features from the parent class, through this hierarchical process the classes share various features, attributes, methods, etc.

What is Java?

Java is a general-purpose programming language that is class-based and object-oriented. Java helps the code developers to quickly write and run the code anywhere without worrying about the computer architecture. It is also known as “Write Once, Run Anywhere(WORA). Once compiled,  the code can run on all platforms without recompilation. The WORA attribute of Java is what makes the Java platform independent, as Java is one of the most highly demanded languages.

Why Java?

  1. Easy to learn.
  2. Object-Oriented Programming Language (OOPs)
  3. Support Multithreading
  4. Multiple platforms friendly
  5. Secure 

The programming language “Java” is widely used in the development of applications for mobile, web, desktop, etc. It is a robust, high-level, and object-oriented programming language developed by Sun Microsystems in 1995. Despite being a programming language, Java has an API and a runtime environment (JRE) and therefore, is also called a platform.

Several concepts are there in Java, with four main concepts to get hold of the language. They are abstraction, encapsulation, inheritance, and polymorphism. 

In this article, we will be focusing on the concept of inheritance in Java and the types of inheritance in java.

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What is Inheritance?

As the name suggests, inheritance means inheriting properties.  The mechanism by which a class is allowed to derive the properties of a different class is termed inheritance.  With the concept of inheritance, the information in a program can be organized hierarchically.

Inheritance is one of the critical features of OOPs (Object Oriented Programming System), where a new class is created from an existing class (parent or base class). In simple terms, the inheritance would mean passing down the characteristics of parents(habits, looks, height) to their child.

The most useful contribution of types of inheritance in java would be the reusability of a code. As discussed earlier that the derived class would inherit the feature, methods, etc from the parent class so the codes present in the parent class would also be inherited into the derived class, this is how reusability would work. Different types of inheritance in java are also mentioned in the article.

In Java, the concept of inheritance allows the users to create classes and use the properties of existing classes. 

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A few important terminologies associated with the concept are:

  • Class: It is defined as a group of objects sharing common properties.
  • Sub Class: Also known as a derived or extended class, this class inherits the features from another class. Also along with the inherited fields and methods, the class generated from the class can add fields and methods of its own.
  • Super Class: The superclass represents the class whose features are inherited by a sub-class.
  • Reusability: The technique of reusability allows the user to create a class (a new one) having the fields or methods of an already existing class. It allows reusing the code.

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Importance of Java inheritance

Implementation of inheritance in Java provides the following benefits:

  • Inheritance minimizes the complexity of a code by minimizing duplicate code. If the same code has to be used by another class, it can simply be inherited from that class to its sub-class. Hence, the code is better organized.
  • The efficiency of execution of a code increases as the code is organized in a simpler form.
  • The concept of polymorphism can be used along with inheritance. 

Syntax

The basic syntax is

Class superclass {

—————- 

}

class subclass extends superclass  

{  

————–

—————– 

}  

The keyword “extends” is used while inheriting a class. It defines that the functionality of the superclass is being extended to the subclass.

The new class created is called a sub-class while the inherited class is termed a parent class.

Two classes Calculation and My_Calculation are created in the above example. The methods addition() and Subtraction() are inherited from the class calculation into the My_Calculation. Keyword extends has been used for inheriting the methods.

The compilation and execution of the above code give the following output.

The creation of the My_Calculation class copies the contents of the superclass into the sub-class. With the objects of the subclass, the users can access the subclass member.

In certain cases when we have to differentiate between the members of the sub-class to that of the superclass having the same names, the keyword “super” is used. If supposedly we have two classes Sub_class and Super_class having the same method i.e. display(). The implementation of the method is different but has the same name. In such a case, to differentiate between the method superclass from that of the sub-class, the super keyword has to be used.

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Types of Java Inheritance

The different types of inheritance are observed in Java:

Figure: 1

1. Single level inheritance

As the name suggests, this type of inheritance occurs for only a single class. Only one class is derived from the parent class. In this type of inheritance, the properties are derived from a single parent class and not more than that. As the properties are derived from only a single base class the reusability of a code is facilitated along with the addition of new features. The flow diagram of a single inheritance is shown below:

Figure 2: Graphical illustration of single-level inheritance

Source

Two classes Class A and Class B are shown in Figure 2, where Class B inherits the properties of Class A.

Example: An example of a code applying single-level inheritance

Source

2. Multi-level Inheritance

The multi-level inheritance includes the involvement of at least two or more than two classes. One class inherits the features from a parent class and the newly created sub-class becomes the base class for another new class.

As the name suggests, in the multi-level inheritance the involvement of multiple base classes is there. In the multilevel inheritance in java,  the inherited features are also from the multiple base classes as the newly derived class from the parent class becomes the base class for another newly derived class.

Figure 3: A flow diagram of multi-level inheritance

Source

From the flow diagram in Figure 3, we can observe that Class B is a derived class from Class A, and Class C is further derived from Class B. Therefore the concept of grandparent class comes into existence in multi-level inheritance.  However, the members of a grandparent’s class cannot be directly accessed in Java.

Therefore, Figure 3 shows that Class C is inheriting the methods and properties of both Class A and Class B.

An example of multi-level inheritance is shown below with three classes X, Y, and Z. The class Y is derived from class X which further creates class Z. 

Example: An example of multi-level inheritance

Source

3. Hierarchical Inheritance

The type of inheritance where many subclasses inherit from one single class is known as Hierarchical Inheritance. 

Hierarchical Inheritance a  combination of more than one type of inheritance.

It is different from the multilevel inheritance, as the multiple classes are being derived from one superclass. These newly derived classes inherit the features, methods, etc, from this one superclass. This process facilitates the reusability of a code and dynamic polymorphism (method overriding).

Figure 4: Graphical representation of a hierarchical inheritance.

In Figure 4, we can observe that the three classes Class B, Class C, and Class D are inherited from the single Class A. All the child classes have the same parent class in hierarchical inheritance.

Example: An example of code showing the concept of hierarchical inheritance

Source

The above code produces the output

meowing…

eating…

Other than these types of inheritance in Java, there are other types known as multiple inheritances and hybrid inheritance. Both types are not supported through classes and can be achieved only through the use of interfaces. 

4. Multiple Inheritance

Multiple inheritances is a type of inheritance where a subclass can inherit features from more than one parent class. Multiple inheritances should not be confused with multi-level inheritance, in multiple inheritances the newly derived class can have more than one superclass. And this newly derived class can inherit the features from these superclasses it has inherited from, so there are no restrictions.  In java, multiple inheritances can be achieved through interfaces.

Figure 5: Representation of multiple inheritances

Source

Figure 4 shows that Class C is derived from the two classes Class A and Class B. In other words it can be described that subclass C inherits properties from both Class A and B.

5. Hybrid Inheritance

Hybrid inheritance is a combination of more than two types of inheritances single and multiple. It can be achieved through interfaces only as multiple inheritance is not supported by Java. It is basically the combination of simple, multiple, hierarchical inheritances.

Figure 6: Representation of a hybrid inheritance

Source

Figure 7

With the different types of inheritance in Java, the ultimate aim is to create sub-classes having properties inherited from the superclasses. The created sub-classes have various properties which are:

  • Fields and methods inherited in a subclass can be directly used.
  • New fields and methods can also be declared in the subclass which is not present in the superclass.
  • A new instance method can be created in the subclass having the same signature as the method in the superclass. The process is referred to as overriding.
  • A new static method can be created in the subclass having the same signature as the method in the superclass. The process is referred to as hiding.

Conclusion

Java is a significant programming language, which makes it suitable for other programming tasks. It is easy to write, and compile than other programming languages. It has multiple applications such as finance, e-commerce, and applications development. Ranked as third-most sought-after programming language for hiring managers globally (PDF, 2.4 MB). It has held #5 spot on Stack Overflow’s list of the most commonly used languages for two years.  Its versatility has contributed to its appeal and demand. Its versatility has contributed to its appeal and demand.

The article discussed the important concept of inheritance in Java and the types of inheritance in Java. Inheritance is therefore the mechanism where we can reuse the codes in order to acquire the properties of a class into another class. This can be achieved through the different types of inheritance patterns as shown in the article. However, there is much more to the concept of inheritance. To excel in the field of development, mastering in the complex programming of Java is required. If you have a dream of innovating intelligent devices, then Executive PG Program in Full-stack Software Development offered by upGrad’s would be the best choice. Certified from the Liverpool John Moores University, the course in association with IIIT Bangalore offers 500+ learning hours and is designed for early professionals. The skill learned from the upGrad’s course will help in opening up opportunities towards the field of software development, web development, javascript developer, etc. Open to any gender within the age group of 21-45, the interactive program might be the best choice for all the coders.

What is inheritance?

Inheritance is a process by which a new object acquires the properties of the previous object. As an example, you can consider a class 'human'. There may be many properties of humans that you want to include in your class such as height, weight, etc. So, one way to do it is to define all those properties again in your class. It may be a good way to learn object-oriented programming but not a good practice. The best way to do it is to inherit all those properties from a particular class. The class 'child' can inherit all the properties of class 'human' (or 'parent'). This is called inheritance in object-oriented programming.

What is object-oriented programming?

Object-oriented programming is a programming paradigm that deals with objects. Each object is usually an instance of a class, which is a programming structure that groups together data and functions that operate on that data. To put it in detail, object-oriented programming is a programming paradigm based on the concept of objects which may contain data, in the form of fields, often known as attributes; and code, in the form of procedures, often known as methods. In some languages, the same word is used for attributes and procedures. Objects are grouped into classes, which are grouped into packages. Each object is an instance of a class, which is a programming structure that groups together data and functions that operate on that data.

What is multiple inheritance?

Multiple inheritance is an object-oriented programming feature in which an object can inherit characteristics from more than one parent class. Also known as a Mixin or composition in disguise, multiple inheritance is often confused with single inheritance and is considered to be a form of it. This is because multiple inheritance and single inheritance are based on different concepts. The concepts of multiple and single inheritance are at opposite ends of a continuum. If single inheritance is based on specialization and polymorphism, multiple inheritance is based on generalization and extensibility.

What are classes in Java?

A class is a template that is used to define objects. Classes are categories and the objects are the items within each category. Class declarations can include the following components- Modifiers- Determines the scope the accessibility of the classes. For example, private, default, protected, or public. Class keyword- Used to create a class. Class name- A class name should begin with the initial letter. (Capitalised by the norm.) Superclass- Determines the name of the class’s parent, if available. Interfaces- Specifies the behavior of the class. Body- Contains all the code that provides the lifecycle of the objects created from the class. It is put within the curly brackets. {}

What is a parent class?

The class whose properties and methods are inherited is called the parent class (base class). The class that inherits the parent properties is called the base class. The base class along with the parent properties can also have its own properties.

How is inheritance achieved in Java?

Inheritance can be achieved using two keywords extends and implements. Extends develop the inheritance between two classes and two interfaces. Whereas, implements develop the inheritance between the class and the interface.

Why multiple inheritance is not supported in java through class?

In multiple inheritance, one class extends two superclasses or base classes. But in Java, one class cannot simultaneously extend more than one class. One class at a time can extend to only one class. Hence, to reduce ambiguity Java does not support multiple inheritance through classes.

How does multiple inheritance implement in Java?

Multiple inheritance can be implemented in Java by using multiple interfaces. One class cannot extend to two classes simultaneously. But one class can implement one or more interfaces. This does not cause ambiguity because the declared methods in the interfaces are implemented in class.

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