Multiple inheritance using interfaces in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is multiple inheritance in Java?

Multiple inheritance means a class can inherit features from more than one parent class or interface. In Java, multiple inheritance is supported only through interfaces, not classes.

beginner

How do interfaces enable multiple inheritance in Java?

A Java class can implement multiple interfaces. This allows the class to inherit abstract methods from many sources, achieving multiple inheritance without the problems of inheriting from multiple classes.

beginner

Can a Java class extend multiple classes?

No, Java does not allow a class to extend more than one class to avoid complexity and ambiguity. Instead, Java uses interfaces to allow multiple inheritance.

intermediate

What happens if two interfaces have methods with the same signature and a class implements both?

The class must provide its own implementation of the method. This resolves any ambiguity because the class decides how to implement the shared method.

beginner

Example: How to declare a class that implements two interfaces named InterfaceA and InterfaceB?

public class MyClass implements InterfaceA, InterfaceB {
    // Implement all abstract methods from InterfaceA and InterfaceB here
}

Which keyword is used in Java to inherit from multiple interfaces?

A inherits

B extends

C implements

D interface

In Java, a class uses the 'implements' keyword to inherit from one or more interfaces.

Can a Java class extend two classes at the same time?

A No, never

B Only if classes are interfaces

C Only if classes are abstract

D Yes, always

Java does not allow a class to extend more than one class to avoid ambiguity.

If two interfaces have the same method signature, what must the implementing class do?

A Use super keyword to call both

B Ignore one method

C Implement both methods separately

D Implement the method once

The class must implement the method once, resolving the conflict.

Which of these is a benefit of using interfaces for multiple inheritance?

A Avoids diamond problem

B Allows multiple constructors

C Enables private inheritance

D Supports multiple superclasses

Interfaces avoid the diamond problem because they only contain abstract methods without state.

How do you declare a class named 'Car' that implements interfaces 'Engine' and 'Wheels'?

A class Car extends Engine, Wheels {}

B class Car implements Engine, Wheels {}

C class Car inherits Engine, Wheels {}

D class Car interface Engine, Wheels {}

The correct syntax uses 'implements' followed by the interface names separated by commas.

Explain how Java supports multiple inheritance using interfaces and why it does not allow multiple inheritance with classes.

Think about how interfaces differ from classes and why Java designers chose this approach.

Describe what happens when a class implements two interfaces that have a method with the same name and signature.

Consider how the class resolves method conflicts from interfaces.