Java 8 – Functional Interfaces

Java 8 – Functional Interfaces

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 BooleanSupplierRepresents a supplier of Boolean-valued results.
6 Consumer<T>Represents an operation that accepts a single input argument and returns no result.
7 DoubleBinaryOperatorRepresents an operation upon two double-valued operands and producing a double-valued result.
8 DoubleConsumerRepresents 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 DoublePredicateRepresents a predicate (Boolean-valued function) of one double-valued argument.
11 DoubleSupplierRepresents a supplier of double-valued results.
12 DoubleToIntFunctionRepresents a function that accepts a double-valued argument and produces an int-valued result.
13 DoubleToLongFunctionRepresents a function that accepts a double-valued argument and produces a long-valued result.
14 DoubleUnaryOperatorRepresents 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 IntBinaryOperatorRepresents an operation upon two int-valued operands and produces an int-valued result.
17 IntConsumerRepresents 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 IntPredicateRepresents a predicate (Boolean-valued function) of one int-valued argument.
20 IntSupplierRepresents a supplier of int-valued results.
21 IntToDoubleFunctionRepresents a function that accepts an int-valued argument and produces a double-valued result.
22 IntToLongFunctionRepresents a function that accepts an int-valued argument and produces a long-valued result.
23 IntUnaryOperatorRepresents an operation on a single int-valued operand that produces an int-valued result.
24 LongBinaryOperatorRepresents an operation upon two long-valued operands and produces a long-valued result.
25 LongConsumerRepresents 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 LongPredicateRepresents a predicate (Boolean-valued function) of one long-valued argument.
28 LongSupplierRepresents a supplier of long-valued results.
29 LongToDoubleFunctionRepresents a function that accepts a long-valued argument and produces a double-valued result.
30 LongToIntFunctionRepresents a function that accepts a long-valued argument and produces an int-valued result.
31 LongUnaryOperatorRepresents 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.

Functional Interface Example

Predicate <T> interface is a functional interface with a method test(Object) to return a Boolean value. This interface signifies that an object is tested to be true or false.

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