javautilfunctionConsumer

java.util.function is a Java package introduced in Java 8 that defines a set of generic functional interfaces designed to work with lambda expressions and method references. It provides standard building blocks for functional-style programming, enabling behavior to be passed as data and composed or transformed.

Core interfaces include Function<T,R>, which represents a function that takes a T and returns an R and exposes the apply method; Predicate<T>, a boolean-valued function of a T with a test method; Consumer<T>, which accepts a T and returns void via the accept method; and Supplier<T>, which supplies a T via the get method. Additionally, UnaryOperator<T> represents a Function<T,T> for single-argument operations, while BinaryOperator<T> represents a BiFunction<T,T,T> for two-argument operations.

The package also provides primitive specializations to avoid boxing and unboxing overhead, such as ToIntFunction<T>, ToLongFunction<T>, and ToDoubleFunction<T>, along with corresponding predicates (IntPredicate, LongPredicate, DoublePredicate), consumers (IntConsumer, LongConsumer, DoubleConsumer), and operators (IntUnaryOperator, LongUnaryOperator, DoubleUnaryOperator, and their binary counterparts). There are also generic functional interfaces like Function, Predicate, and Consumer with specific primitive mapped variants.

Common usage patterns include using Function as map in streams, Predicate for filtering, and Consumer for side-effect actions, with Supplier used to produce values. Default and static methods in these interfaces provide composition utilities, such as Function.andThen and Function.compose, and Predicate’s and, or, and negate, enabling flexible building of complex behavior from simple components. Overall, java.util.function provides a standard, type-safe toolkit for expressing behavioral logic in a functional style.