@Documented @Retention(RUNTIME) @Target(TYPE) public @interface FunctionalInterface
java.lang.Object
, that also does not count toward the interface's abstract method count since any implementation of the interface will have an implementation from java.lang.Object
or elsewhere. Note that instances of functional interfaces can be created with lambda expressions, method references, or constructor references.
If a type is annotated with this annotation type, compilers are required to generate an error message unless:
However, the compiler will treat any interface meeting the definition of a functional interface as a functional interface regardless of whether or not a FunctionalInterface
annotation is present on the interface declaration.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/FunctionalInterface.html