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lambdajava-8functional-programmingmarker-interfaces
AdityaKapreShrewsburyBoston
AdityaKapreShrewsburyBoston

Reputation: 1143

Is @FunctionalInterface just a marker interface or more than that?

I guess @FuntionalInterface is present even before Java 8 (although not directly named as @FunctionalInterface the interfaces such as Comparator and Comparable that have single method). Is it just a marker interface or will it trigger compiler checks to make sure that the interface contains one and only one method which can be used in lambda expression ?

Upvotes: -1

Views: 260

Answers (1)

Turing85
Turing85

Reputation: 20185

It is not even a marker. From the @FunctionalInterface API:

An informative annotation type used to indicate that an interface type declaration is intended to be a functional interface as defined by the Java Language Specification.

(Highlighting added by me)

It is additionally annotated with @Documented, thus the presence of this annotation will be present in, for example, javadocs.

It provides, however, some compile time safety. If the annotated interface has more than one non-default method, we will receive a compilation error.

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Upvotes: 1

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