Can an Interface Be a Data Type in Java?


Scott Campbell

An interface in Java is a reference type that is similar to a class. It is a collection of abstract methods that are used to define a contract for the classes that implement it. In other words, an interface specifies what methods a class must implement, but does not provide the implementation details.

Can an Interface Be a Data Type?

Yes, an interface can be used as a data type in Java. This means that you can declare variables of an interface type and use them to hold objects of any class that implements that interface.

Let’s consider an example where we have two classes: Circle and Rectangle. Both of these classes implement the Shape interface, which defines the method calculateArea(). Here’s how we can declare variables of the Shape interface:

  • Shape circle = new Circle();
  • Shape rectangle = new Rectangle();

In this example, both circle and rectangle are declared as variables of the Shape interface type. This allows us to treat objects of different classes that implement the Shape interface in a similar way.

The Benefits of Using Interfaces as Data Types

The use of interfaces as data types provides several benefits:

  1. Polymorphism: By using interfaces as data types, we can achieve polymorphism. Polymorphism allows us to write code that works with objects of different classes in a unified manner.
  2. Flexible Design: Using interfaces as data types promotes loose coupling between classes.

    This means that we can easily change the implementation details of a class without affecting other parts of the code.

  3. Code Reusability: Interfaces allow us to define common behavior that can be implemented by multiple classes. This promotes code reusability and reduces code duplication.

It’s important to note that while we can use an interface as a data type, we cannot create instances of an interface using the new keyword. Instead, we need to create objects of classes that implement the interface and assign them to variables of the interface type.


In Java, an interface can indeed be used as a data type. It allows us to write flexible and reusable code by providing a contract for classes to implement. By using interfaces as data types, we can achieve polymorphism, promote loose coupling between classes, and enhance code reusability.

So go ahead and leverage the power of interfaces in your Java programs!

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