Java Inheritance: Is Multiple Inheritance Supported?

Java Inheritance: Multiple vs. Multi-Level

In Java, the concept of inheritance allows a class to inherit properties and behaviors from another class. However, the question of whether Java supports multiple inheritance (i.e., inheriting from multiple base classes) has sparked some debate.

The Interviewer's Statement

An interviewer presented a scenario where class A extends class B, and class B extends the Object class. They argued that since A inherits from B and ultimately from Object, this constitutes multiple inheritance.

Your Response

Your response, citing that B inherits from Object, correctly clarified that this scenario represents multi-level inheritance rather than multiple inheritance.

Defining Multiple Inheritance

Multiple inheritance refers to a situation where a class inherits properties and behaviors from two or more unrelated base classes. In Java, this type of inheritance is not supported.

Multi-Level Inheritance

Multi-level inheritance occurs when a class inherits from another class, which in turn inherits from another class, and so on. In the given scenario, A extends B, and B extends Object, creating a chain of inheritance rather than multiple branches.

Implementation Details

Internally, the JVM resolves member access from an object by searching for the member in the object's type or in the type it inherits from. In the example given, an instance of class A can access members from both A and B because B indirectly provides access to members inherited from Object.

Java 8 and Default Interface Methods

While Java does not support true multiple inheritance, the introduction of default interface methods in Java 8 has introduced some complexities. Default interface methods allow interfaces to provide default implementations for their methods. When a class implements an interface, it can inherit these default methods, even if it does not provide its own implementation. This can simulate the effects of multiple inheritance to some extent. However, it avoids some of the potential pitfalls of true multiple inheritance, such as method ambiguity and constructor conflicts.

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