Difference Between Interface and Abstract Class in Java

Difference Between Interface and Abstract Class in Java (With Examples)

If you're learning Java, one of the most common interview questions is the difference between interface and abstract class.

Understanding this difference helps you design better and scalable Java applications.

Choosing between interface and abstract class helps you design flexible and scalable Java applications.

This is a frequently asked topic in Java interviews.

Written by Shivkumar Udas – Engineering student sharing practical Java guides for beginners.

💡 What is an Abstract Class?

An abstract class is a class that cannot be instantiated and may contain both abstract and non-abstract methods.

abstract class Animal {
    abstract void sound();

    void sleep() {
        System.out.println("Sleeping");
    }
}

Key Point: Can have both implemented and unimplemented methods.

💡 What is an Interface?

An interface is a blueprint of a class that contains only abstract methods (before Java 8).

interface Animal {
    void sound();
}

Key Point: Used to achieve full abstraction.

📊 Difference Between Interface and Abstract Class

Feature	Abstract Class	Interface
Methods	Abstract + Non-abstract	Only abstract (before Java 8)
Inheritance	Single inheritance	Multiple inheritance
Variables	Can have instance variables	Only constants
Keyword	extends	implements

⚡ When to Use Abstract Class?

• When classes share common functionality
• When partial abstraction is needed

⚡ When to Use Interface?

• When full abstraction is required
• When multiple inheritance is needed

🔍 Real-Life Example

Abstract Class: A vehicle can have common methods like start() and stop().

Interface: Different vehicles can implement different behaviors like fly() or drive().

🎯 Interview Tip

Remember: Abstract class = partial abstraction, Interface = full abstraction.

Interfaces are widely used in modern Java development.

🧪 Practice Task

Create an abstract class and an interface, and implement them in a Java program.

🔗 Related Guides

• OOP Concepts
• Java Collections Framework
• Java Interview Questions

🎯 Conclusion

Understanding the difference between interface and abstract class helps you design better Java applications.

Choose based on your use case and design requirements.