Why is Multiple Inheritance Not Supported in Java?

In most of the coding interviews, recruiters ask why multiple inheritance in Java is not supported directly. While we know that multiple inheritance is one of the main Java inheritance types, it is only supported by an interface. 

This is because the problem is driven by the methods and designs chosen by a programmer.

To help you out with why Java doesn’t support this inheritance, we have compiled every possible data that will give you enough insight. 

We will be covering the aspects of inheritance and the reason behind multiple inheritance is not backed up by Java.

Without much ado, let’s get ahead.

What is Inheritance?

Inheritance refers to the mechanism that allows one class to derive properties from another. The information in a program can be organized hierarchically using the concept of inheritance. One of the most important features of OOPs (Object Oriented Programming System) is inheritance, which allows a new class to be created from an existing class (parent or base class). 

The most useful contribution of inheritance types in Java would be code reusability.

The inheritance concept in Java allows users to create classes and use the properties of existing classes.

Types of Inheritance in Java

There are five types of Java inheritance and they are,

• Single-level inheritance

• Multi-level Inheritance

• Hierarchical Inheritance

• Multiple Inheritance

• Hybrid Inheritance

Unlike single, multi and hierarchical inheritance in Java, Multiple and Hybrid Inheritance are not directly supported by Java without the use of an interface. Moreover, single inheritance also in many cases gets backed via an interface for they cause similar ambiguities like multiple inheritance.

Below we will look at what a Multiple inheritance in Java is and the causes behind using an interface.

What is Multiple Inheritance in Java?

Multiple inheritance entails the ability to build a single class along with many superclasses. Java does not enable multiple inheritance in classes, unlike C++ and other prominent programming languages. It is because it can cause an issue known as the diamond problem. Additionally, to avoid this problem and to have better results, there are multiple ways thus programmers avoid supporting multiple inheritance in Java.

Reasons Why Multiple Inheritance in Java is Unsupported

There are mainly two reasons why multiple inheritance is only done using an interface and is not Java supported. The reasons are:

Causes Diamond Problem

The first reason why Multiple inheritance in Java can’t get backed is the uncertainty in the Diamond problem. 

For example, Let’s take class W that has a foodbar. Then, note how X and Y that come from W also have their own foobar, that is, foo (). Now, you can see how Z, which comes from X and Y, causes confusion. Due to every class having a foobar, the compiler will not know which class’ foobar to choose to get the final output. Thus, it causes the diamond problem as the program looks like diamond in shape.

Even if we remove class W which is the head of all the other classes, the same problem will arise. While in C++ this problem can be supported in Java it cannot be used because who wants to encounter a diamond problem when if they use an interface this problem can be cut down?

Causes Complexities

When we make Java back multiple inheritance, it will complicate the code, design and also bring problems while we cast, construct chains and so on. Moreover, multiple inheritance isn’t really necessary when there are alternatives with better results. So most programmers avoid this method and bring in simple structures.

How is Multiple Inheritance Done?

As we know, it is through the help of an interface. Now what is an interface? In Java, an interface is the design of a class that gives a technique to accomplish abstraction. It has a collection of abstract methods that describe the optional ability that your class should comply with. This is where interface comes to help with the solution.

Why Need an Interface to Solve Multiple Interfaces?

As multiple inheritance creates complexity and a diamond problem, using an interface can eradicate it. An interface is nothing but a class with a set of methods that will help specify what a class should do rather than how it can do.

As a result, when a class makes use of an interface, it takes in all of the interface's sets of methods and provides an execution for each class.

Interfaces are quasi and represent what a class should execute as they do not provide accurate instructions for its behavior. As a result of this feature, a class can execute infinite interfaces without problems because the class itself on its own executes. 

Using the interface, we can easily dodge all the complexities and achieve multiple inheritance in Java. Similarly, hierarchical inheritance in Java can also be achieved via interface alone. 

Final Thoughts

To solve a multiple inheritance, usually programmers try to avoid complications, thus adding the help of an inheritance. We hope you received enough information on why multiple inheritance in Java has ambiguities, how else can it be solved and other important details regarding inheritance. 

Additionally, if you are asked about this in an interview, we believe you will be able to crack the answer to them with our information.