IntelliJ IDEA's Extract Interface Refactoring

Extract Interface creates a new interface from selected members of an existing class, helping separate an abstraction from its implementation. JetBrains documents that the refactoring creates the interface without applying it immediately, so the source class remains unchanged until you confirm further changes.

Yes, the refactoring dialog lets you select the class members that should become interface methods. This is useful when a class has many methods but only a smaller public contract should be exposed to other Java or Kotlin code.

The Extract Interface action first creates the interface and does not immediately change the source class, according to JetBrains documentation. Review the preview and apply the implementation relationship only when it matches the intended design.

It is useful when callers should depend on a narrow contract instead of a concrete class, such as when introducing mocks for tests or multiple implementations. The operation is part of IntelliJ IDEA's Refactor menu and can reduce coupling without manually copying method signatures.