🤔 Can an Interface Extend Itself in Java?

Java’s interface mechanism allows developers to define contracts that classes must fulfill. Interfaces can extend other interfaces, enabling reuse and layering of behavior.

But what happens if an interface tries to extend itself?

Can an interface extend itself in Java?

It might sound like an edge case or theoretical curiosity — but it’s actually a great way to understand how Java handles inheritance cycles and why some rules exist in the first place.

Let’s get into it.

What Does “Extending Itself” Mean?

In Java, one interface can extend another like this:

interface A {
    void doSomething();
}

interface B extends A {
    void doMore();
}

But what if we try:

interface A extends A {
    void doSomething();
}

This is asking: can an interface be its own parent?

🚫 The Answer: No, Java Does Not Allow This

Java does not allow an interface to extend itself, directly or indirectly.

Trying to do so will cause a compile-time error.

Let’s Test It

Here’s a minimal example:

public interface A extends A {
    void doSomething();
}