Extends keyword in Java vs. Implements keyword in Java: Know the Difference
By Hifza Nasir & Dua Fatima || Published on May 28, 2026
The extends keyword in Java is used for class inheritance, allowing a class to inherit from another class, whereas implements is used by a class to adhere to an interface, defining methods the class must implement.
Key Differences
The extends keyword in Java signifies class inheritance, enabling a class to inherit properties and methods from a single superclass. This mechanism is foundational for achieving polymorphism and code reuse. Conversely, the implements keyword is utilized when a class agrees to implement an interface, a contract that mandates the implementation of all abstract methods defined within the interface. This approach promotes a form of polymorphism and flexibility, allowing a class to conform to multiple interfaces.
Hifza Nasir
May 28, 2026
Extends facilitates the creation of a hierarchical relationship between classes, emphasizing the is-a relationship, implements focuses on the has-a capability, enabling a class to acquire certain functionalities defined by interfaces. This distinction highlights Java's support for single inheritance (via extends) and multiple implementations (via implements).
Dua Fatima
May 28, 2026
The use of extends is restricted to classes only, meaning a class can only extend another class. It cannot extend multiple classes due to Java's single inheritance principle. In contrast, implements allows a class to adhere to multiple interfaces, overcoming the limitation of single inheritance by enabling a class to exhibit multiple behaviors.
Hifza Nasir
May 28, 2026
Extends is used when there is a clear hierarchical relationship needing property and method sharing. On the other hand, implements is chosen when a class must guarantee the implementation of certain behaviors, offering a way to enforce consistency across different classes without enforcing a strict parent-child class relationship.
Dua Fatima
May 28, 2026
The choice between extends and implements reflects design intent: extends is for extending functionality of existing classes, while implements is for agreeing to fulfill a contract of methods, enabling diverse classes to work interchangeably within the same framework or API.
Shumaila Saeed
May 28, 2026
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Comparison Chart
Usage
For class inheritance, allowing a class to inherit from another class.
For implementing interfaces, requiring a class to implement specified methods.
Dua Fatima
May 28, 2026
Inheritance Type
Single inheritance, can extend only one class.
Multiple inheritance, can implement multiple interfaces.
Hifza Nasir
May 28, 2026
Relationship Type
Is-a relationship, indicating a specific type of hierarchy.
Has-a capability, indicating possession of certain functionalities.
Hifza Nasir
May 28, 2026
Compatibility
Only between classes.
Between a class and one or more interfaces.
Shumaila Saeed
May 28, 2026
Functionality
Inherits all non-private members (methods and fields) from the parent class.
Must implement all abstract methods defined in the interface(s).
Dua Fatima
May 28, 2026
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Extends keyword in Java and Implements keyword in Java Definitions
Extends keyword in Java
Supports constructor chaining via super().
Super(parameters); in a subclass constructor.
Dua Fatima
Feb 26, 2024
Implements keyword in Java
Used by classes to agree to implement the methods of an interface.
Public class MyClass implements MyInterface {}.
Dua Fatima
Feb 26, 2024
Extends keyword in Java
Allows for polymorphic behavior through inheritance.
Animal myDog = new Dog();.
Hifza Nasir
Feb 26, 2024
Implements keyword in Java
Requires concrete implementations of all abstract methods in the interface.
Public void myMethod() {} as defined in MyInterface.
Dua Fatima
Feb 26, 2024
Extends keyword in Java
Facilitates the use of super to access superclass methods and properties.
Super.methodName();.
Hifza Nasir
Feb 26, 2024
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Implements keyword in Java
Enables a class to be more formally polymorphic.
MyInterface myClass = new MyClass();.
Hifza Nasir
Feb 26, 2024
Extends keyword in Java
Used to inherit the properties and methods of one class into another.
Public class Dog extends Animal {} means Dog inherits from Animal.
Dua Fatima
Feb 26, 2024
Implements keyword in Java
Allows a class to adhere to multiple interfaces.
Public class MyClass implements Interface1, Interface2 {}.
Hifza Nasir
Feb 26, 2024
Extends keyword in Java
Enables method overriding to provide specific implementations.
@Override in a subclass method.
Dua Fatima
Feb 26, 2024
Implements keyword in Java
Enforces method signatures consistency across different classes.
Consistent method implementations as per interface contract.
Hifza Nasir
Feb 26, 2024
Repeatedly Asked Queries
Why can't Java classes extend multiple classes?
Java supports single inheritance to avoid complexity and ambiguity associated with multiple inheritances.
Hifza Nasir
May 28, 2026
Can interfaces extend other interfaces?
Yes, interfaces can extend other interfaces, allowing for a hierarchy of interfaces.
Hifza Nasir
May 28, 2026
Can a class use both extends and implements?
Yes, a class can extend another class and implement one or more interfaces simultaneously.
Hifza Nasir
May 28, 2026
Can a class extend an interface?
No, a class cannot extend an interface; it can only implement interfaces.
Dua Fatima
May 28, 2026
Can interfaces contain implemented methods?
Yes, from Java 8 onwards, interfaces can contain default and static methods with implementations.
Shumaila Saeed
May 28, 2026
What is the extends keyword used for?
It's used for class inheritance in Java, allowing one class to inherit from another.
Dua Fatima
May 28, 2026
What does the implements keyword do?
It allows a class to implement an interface, requiring it to define the methods declared in the interface.
Hifza Nasir
May 28, 2026
What is method overriding, and how does it relate to extends?
Method overriding is defining a method in a subclass that has the same signature as a method in its superclass, allowing the subclass to provide a specific implementation.
Hifza Nasir
May 28, 2026
What happens if a class does not implement all methods of an interface?
The class must be declared abstract, or it will result in a compilation error.
Dua Fatima
May 28, 2026
Is it possible to implement multiple interfaces?
Yes, a class can implement multiple interfaces, making it versatile in its functionality.
Hifza Nasir
May 28, 2026
What's the difference between extending a class and implementing an interface?
Extending a class inherits its properties and methods, while implementing an interface requires defining the methods declared in the interface.
Hifza Nasir
May 28, 2026
How do extends and implements impact software design?
They encourage code reuse, polymorphism, and flexibility, enabling more modular and maintainable software design.
Hifza Nasir
May 28, 2026
How does extends affect constructors?
Constructors are not inherited; however, a subclass can call a superclass constructor using super().
Dua Fatima
May 28, 2026
How do extends and implements contribute to polymorphism?
extends allows for polymorphic behavior through inheritance, while implements enables it by allowing classes to be interchangeable through common interfaces.
Dua Fatima
May 28, 2026
Can a class extend more than one interface?
The phrasing should be "implement more than one interface," and yes, it can.
Shumaila Saeed
May 28, 2026
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About Author
Written by
Hifza Nasir
Co-written by
Dua Fatima
Hifza Nasir
Dua Fatima
Shumaila Saeed
