Functional Interfaces -- JAVA8

Functional interfaces have a single functionality to exhibit. For example, a Comparable interface with a single method ‘compareTo’ is used for comparison purpose. Java 8 has defined a lot of functional interfaces to be used extensively in lambda expressions. Following is the list of functional interfaces defined in java.util.Function package.

S. No.	Interface & Description
1	BiConsumer<T,U> Represents an operation that accepts two input arguments, and returns no result.
2	BiFunction<T,U,R> Represents a function that accepts two arguments and produces a result.
3	BinaryOperator<T> Represents an operation upon two operands of the same type, producing a result of the same type as the operands.
4	BiPredicate<T,U> Represents a predicate (Boolean-valued function) of two arguments.
5	BooleanSupplier Represents a supplier of Boolean-valued results.
6	Consumer<T> Represents an operation that accepts a single input argument and returns no result.
7	DoubleBinaryOperator Represents an operation upon two double-valued operands and producing a double-valued result.
8	DoubleConsumer Represents an operation that accepts a single double-valued argument and returns no result.
9	DoubleFunction<R> Represents a function that accepts a double-valued argument and produces a result.
10	DoublePredicate Represents a predicate (Boolean-valued function) of one double-valued argument.
11	DoubleSupplier Represents a supplier of double-valued results.
12	DoubleToIntFunction Represents a function that accepts a double-valued argument and produces an int-valued result.
13	DoubleToLongFunction Represents a function that accepts a double-valued argument and produces a long-valued result.
14	DoubleUnaryOperator Represents an operation on a single double-valued operand that produces a double-valued result.
15	Function<T,R> Represents a function that accepts one argument and produces a result.
16	IntBinaryOperator Represents an operation upon two int-valued operands and produces an int-valued result.
17	IntConsumer Represents an operation that accepts a single int-valued argument and returns no result.
18	IntFunction<R> Represents a function that accepts an int-valued argument and produces a result.
19	IntPredicate Represents a predicate (Boolean-valued function) of one int-valued argument.
20	IntSupplier Represents a supplier of int-valued results.
21	IntToDoubleFunction Represents a function that accepts an int-valued argument and produces a double-valued result.
22	IntToLongFunction Represents a function that accepts an int-valued argument and produces a long-valued result.
23	IntUnaryOperator Represents an operation on a single int-valued operand that produces an int-valued result.
24	LongBinaryOperator Represents an operation upon two long-valued operands and produces a long-valued result.
25	LongConsumer Represents an operation that accepts a single long-valued argument and returns no result.
26	LongFunction<R> Represents a function that accepts a long-valued argument and produces a result.
27	LongPredicate Represents a predicate (Boolean-valued function) of one long-valued argument.
28	LongSupplier Represents a supplier of long-valued results.
29	LongToDoubleFunction Represents a function that accepts a long-valued argument and produces a double-valued result.
30	LongToIntFunction Represents a function that accepts a long-valued argument and produces an int-valued result.
31	LongUnaryOperator Represents an operation on a single long-valued operand that produces a long-valued result.
32	ObjDoubleConsumer<T> Represents an operation that accepts an object-valued and a double-valued argument, and returns no result.
33	ObjIntConsumer<T> Represents an operation that accepts an object-valued and an int-valued argument, and returns no result.
34	ObjLongConsumer<T> Represents an operation that accepts an object-valued and a long-valued argument, and returns no result.
35	Predicate<T> Represents a predicate (Boolean-valued function) of one argument.
36	Supplier<T> Represents a supplier of results.
37	ToDoubleBiFunction<T,U> Represents a function that accepts two arguments and produces a double-valued result.
38	ToDoubleFunction<T> Represents a function that produces a double-valued result.
39	ToIntBiFunction<T,U> Represents a function that accepts two arguments and produces an int-valued result.
40	ToIntFunction<T> Represents a function that produces an int-valued result.
41	ToLongBiFunction<T,U> Represents a function that accepts two arguments and produces a long-valued result.
42	ToLongFunction<T> Represents a function that produces a long-valued result.
43	UnaryOperator<T> Represents an operation on a single operand that produces a result of the same type as its operand.