Java has many frequently used functional interfaces in the package java.util.function.
The following table lists Functional Interfaces Declared in the Package java.util.function
| Interface Name | Method | Description |
|---|---|---|
| Function<T,R> | R apply(T t) | a function that takes an argument of type T and returns a result of type R. |
| BiFunction<T,U,R> | R apply(T t, U u) | a function that takes two arguments of types T and U, and returns a result of type R. |
| Predicate<T> | boolean test(T t) | represents a condition that returns true or false for the specified argument. |
| BiPredicate<T,U> | boolean test(T t, U u) | a predicate with two arguments. |
| Consumer<T> | void accept(T t) | an operation that takes an argument, operates on it to produce some side effects, and returns no result. |
| BiConsumer<T,U> | void accept(T t, U u) | an operation that takes two arguments, operates on them to produce some side effects, and returns no result. |
| Supplier<T> | T get() | a supplier that returns a value. |
| UnaryOperator<T> | T apply(T t) | Inherits from Function<T,T>. Represents a function that takes an argument and returns a result of the same type. |
| BinaryOperator<T> | T apply(T t1, T t2) | Inherits from BiFunction<T,T,T>. Represents a function that takes two arguments of the same type and returns a result of the same. |
There are several specialized versions of interfaces above.
For example, IntConsumer is a specialized version of Consumer<T>.