Why do we have @functionalInterface if we can make any interface as functional interface if it already has one abstract method?

Question

Accepted Answer

Functional interfaces provide clarity and enforce single abstract method constraint.

Functional interfaces provide clarity to developers by explicitly indicating that the interface is intended to be used as a functional interface.
Using @FunctionalInterface annotation helps enforce the single abstract method constraint, preventing accidental addition of more abstract methods.
It also allows the compiler to perform additional checks to ensure that the interface meets the requirements of a functional interface.
Examples of functional interfaces in Java include Runnable, Callable, and ActionListener.

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