Interface Summary
Interface	Description
BinaryOperator<T>	An operation upon two operands yielding a result.
Block<T>	An operation upon an input object.
DoubleBinaryOperator	An operation on two `double` operands yielding a `double` result.
DoubleBlock	An operation upon a `double` input value.
DoubleFunction<T>	Apply a function to the input object yielding an appropriate `double` value; this is the `double`-bearing specialization for `Function`.
DoubleSupplier	A supplier of `double` values.
DoubleUnaryOperator	An operation on a single `double` operand yielding a `double` result.
Function<T,R>	Apply a function to the input object yielding an appropriate result object.
IntBinaryOperator	An operation on two `int` operands yielding an `int` result.
IntBlock	An operation upon an `int` input value.
IntFunction<T>	Apply a function to the input object yielding an appropriate `int` value; this is the `int`-bearing specialization for `Function`.
IntSupplier	A supplier of `int` values.
IntUnaryOperator	An operation on a single `int` operand yielding an `int` result.
LongBinaryOperator	An operation on two `long` operands yielding a `long` result.
LongBlock	An operation upon a `long` input value.
LongFunction<T>	Apply a function to the input object yielding an appropriate `long` value; this is the `long`-bearing specialization for `Function`.
LongSupplier	A supplier of `long` values.
LongUnaryOperator	An operation on a single `long` operand yielding a `long` result.
Predicate<T>	Determines if the input object matches some criteria.
Supplier<T>	A supplier of objects.
UnaryOperator<T>	An operation upon a single operand yielding a result.

Package java.util.function Description

Functional interfaces provide typing for lambda expressions. Each functional interface provides a single abstract method to which the lambda expression's parameter and return types are matched.

The interfaces in this package are all functional interfaces used with the collections and streams frameworks. The operation identified by each interface is generally applied to a collection or stream of objects.

All functional interface implementations are expected to ensure that:

When used for aggregate operations upon many elements it should not be assumed that the operation will be called upon elements in any specific order.
null values are accepted and returned by these functional interfaces according to the constraints of the specification in which the functional interfaces are used. The functional interfaces themselves do not constrain or mandate use of null values. Most usages of the functional interfaces will define the role, if any, of null for that context.

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For further API reference and developer documentation, see Java SE Documentation . That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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