Package java.util.function
     // Assignment context
     Predicate<String> p = String::isEmpty;
     // Method invocation context
     stream.filter(e -> e.getSize() > 10)...
     // Cast context
     stream.map((ToIntFunction) e -> e.getSize())...
 The interfaces in this package are general purpose functional interfaces
 used by the JDK, and are available to be used by user code as well.  While
 they do not identify a complete set of function shapes to which lambda
 expressions might be adapted, they provide enough to cover common
 requirements. Other functional interfaces provided for specific purposes,
 such as FileFilter, are defined in the packages where they
 are used.
 
The interfaces in this package are annotated with
 FunctionalInterface. This annotation is not a requirement
 for the compiler to recognize an interface as a functional interface, but
 merely an aid to capture design intent and enlist the help of the compiler in
 identifying accidental violations of design intent.
 
Functional interfaces often represent abstract concepts like functions, actions, or predicates. In documenting functional interfaces, or referring to variables typed as functional interfaces, it is common to refer directly to those abstract concepts, for example using "this function" instead of "the function represented by this object". When an API method is said to accept or return a functional interface in this manner, such as "applies the provided function to...", this is understood to mean a non-null reference to an object implementing the appropriate functional interface, unless potential nullity is explicitly specified.
The functional interfaces in this package follow an extensible naming convention, as follows:
- There are several basic function shapes, including
     Function(unary function fromTtoR),Consumer(unary function fromTtovoid),Predicate(unary function fromTtoboolean), andSupplier(nullary function toR).
- Function shapes have a natural arity based on how they are most
     commonly used.  The basic shapes can be modified by an arity prefix to
     indicate a different arity, such as
     BiFunction(binary function fromTandUtoR).
- There are additional derived function shapes which extend the basic
     function shapes, including UnaryOperator(extendsFunction) andBinaryOperator(extendsBiFunction).
- Type parameters of functional interfaces can be specialized to
     primitives with additional type prefixes.  To specialize the return type
     for a type that has both generic return type and generic arguments, we
     prefix ToXxx, as inToIntFunction. Otherwise, type arguments are specialized left-to-right, as inDoubleConsumerorObjIntConsumer. (The type prefixObjis used to indicate that we don't want to specialize this parameter, but want to move on to the next parameter, as inObjIntConsumer.) These schemes can be combined, as inIntToDoubleFunction.
- If there are specialization prefixes for all arguments, the arity
     prefix may be left out (as in ObjIntConsumer).
- Since:
- 1.8
- See Also:
- 
InterfacesClassDescriptionBiConsumer<T,U> Represents an operation that accepts two input arguments and returns no result.BiFunction<T,U, R> Represents a function that accepts two arguments and produces a result.Represents an operation upon two operands of the same type, producing a result of the same type as the operands.BiPredicate<T,U> Represents a predicate (boolean-valued function) of two arguments.Represents a supplier ofboolean-valued results.Consumer<T>Represents an operation that accepts a single input argument and returns no result.Represents an operation upon twodouble-valued operands and producing adouble-valued result.Represents an operation that accepts a singledouble-valued argument and returns no result.Represents a function that accepts a double-valued argument and produces a result.Represents a predicate (boolean-valued function) of onedouble-valued argument.Represents a supplier ofdouble-valued results.Represents a function that accepts a double-valued argument and produces an int-valued result.Represents a function that accepts a double-valued argument and produces a long-valued result.Represents an operation on a singledouble-valued operand that produces adouble-valued result.Function<T,R> Represents a function that accepts one argument and produces a result.Represents an operation upon twoint-valued operands and producing anint-valued result.Represents an operation that accepts a singleint-valued argument and returns no result.IntFunction<R>Represents a function that accepts an int-valued argument and produces a result.Represents a predicate (boolean-valued function) of oneint-valued argument.Represents a supplier ofint-valued results.Represents a function that accepts an int-valued argument and produces a double-valued result.Represents a function that accepts an int-valued argument and produces a long-valued result.Represents an operation on a singleint-valued operand that produces anint-valued result.Represents an operation upon twolong-valued operands and producing along-valued result.Represents an operation that accepts a singlelong-valued argument and returns no result.LongFunction<R>Represents a function that accepts a long-valued argument and produces a result.Represents a predicate (boolean-valued function) of onelong-valued argument.Represents a supplier oflong-valued results.Represents a function that accepts a long-valued argument and produces a double-valued result.Represents a function that accepts a long-valued argument and produces an int-valued result.Represents an operation on a singlelong-valued operand that produces along-valued result.Represents an operation that accepts an object-valued and adouble-valued argument, and returns no result.Represents an operation that accepts an object-valued and aint-valued argument, and returns no result.Represents an operation that accepts an object-valued and along-valued argument, and returns no result.Predicate<T>Represents a predicate (boolean-valued function) of one argument.Supplier<T>Represents a supplier of results.ToDoubleBiFunction<T,U> Represents a function that accepts two arguments and produces a double-valued result.Represents a function that produces a double-valued result.ToIntBiFunction<T,U> Represents a function that accepts two arguments and produces an int-valued result.Represents a function that produces an int-valued result.ToLongBiFunction<T,U> Represents a function that accepts two arguments and produces a long-valued result.Represents a function that produces a long-valued result.Represents an operation on a single operand that produces a result of the same type as its operand.