10 Differences Between abstract and interface

Abstract vs Interface: Understanding the Differences

What is/are abstract?

An abstract class is a blueprint for creating objects that have common properties and behaviors. It cannot be instantiated on its own; instead, it serves as a base for deriving subclasses. Abstract classes may contain abstract methods, which are declared but do not have an implementation.

Examples of abstract

Here are a few examples of abstract classes:

  • Animal: An abstract class representing common properties and methods for animals.
  • Shape: An abstract class that defines common attributes and methods for different shapes.
  • Vehicle: An abstract class for vehicles, specifying common characteristics and behaviors.

Uses of abstract

Abstract classes provide a way to define common functionality across multiple classes. They enable code reusability and promote a hierarchical structure in object-oriented programming.

What is/are interface?

An interface is a contract that defines a set of methods that a class must implement. It specifies the methods a class should have without providing their implementations. In other words, an interface defines what a class can do, but not how it does it.

Examples of interface

Some examples of interfaces include:

  • Comparable: An interface that determines the natural ordering of objects.
  • Iterable: An interface that allows objects to be iterated over using the foreach loop.
  • Serializable: An interface that enables objects to be serialized and deserialized.

Uses of interface

Interfaces allow multiple classes to share common behavior by implementing the same set of methods. They enable polymorphism and provide a way to achieve loose coupling between objects.

Differences Table

Difference Area Abstract vs Interface
Abstract Interface
Instantiation Cannot be instantiated directly Cannot be instantiated directly
Extensibility Allows single inheritance, but can implement multiple interfaces Allows implementing multiple interfaces, but no inheritance
Implementation Can have implemented methods in addition to abstract methods Can only have method signatures without implementations
Fields Can have instance variables, constants, and static variables Can only have constants (static final variables)
Accessibility Can have different access modifiers for different methods All methods are implicitly public
Number A class can extend only one abstract class A class can implement multiple interfaces
Inheritance Allows for the inheritance of non-abstract methods and fields Does not support inheritance of methods or fields
Design Focus Primarily focuses on code reuse and common behavior Primarily focuses on specifying behavior and achieving loose coupling
Keyword Uses the keyword “extends” Uses the keyword “implements”


In summary, abstract classes and interfaces are both essential tools in object-oriented programming. While abstract classes provide a way to define common behavior and allow some flexibility, interfaces focus on specifying behavior and promoting loose coupling. Understanding the differences between them will help you make the best design decisions in your projects.

People Also Ask

1. Can an abstract class implement an interface?

Yes, an abstract class can implement an interface. By doing so, it fulfills the contract specified by the interface and provides an implementation for the interface’s methods.

2. Can a class inherit from multiple abstract classes?

No, a class in Java can only inherit from a single abstract class. This is a limitation of single inheritance. However, a class can implement multiple interfaces to achieve similar functionality.

3. Can abstract classes have constructors?

Yes, abstract classes can have constructors. These constructors are typically used to initialize the instance variables of the abstract class or perform any other necessary setup.

4. Can interfaces have instance variables?

No, interfaces cannot have instance variables. They can only have constants, which are declared as static final variables.

5. Can abstract classes have static methods?

Yes, abstract classes can have static methods. These methods belong to the class itself and can be called without creating an instance of the class.

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