Function (Java SE 9 & JDK 9 ) (original) (raw)

• Type Parameters:
  T - the type of the input to the function
  R - the type of the result of the function
  All Known Subinterfaces:
  [UnaryOperator](../../../java/util/function/UnaryOperator.html "interface in java.util.function")<T>
  Functional Interface:
  This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface Function<T,R>
Since:
1.8

• • Method Summary

  All Methods Static Methods Instance Methods Abstract Methods Default Methods

  Modifier and Type	Method	Description
  default Function<T,V>	andThen​(Function<? super R,? extends V> after)	Returns a composed function that first applies this function to its input, and then applies the after function to the result.
  R	apply​(T t)	Applies this function to the given argument.
  default Function<V,R>	compose​(Function<? super V,? extends T> before)	Returns a composed function that first applies the before function to its input, and then applies this function to the result.
  static Function<T,T>	identity​()	Returns a function that always returns its input argument.

• • Method Detail

     * #### apply  
     [R](../../../java/util/function/Function.html "type parameter in Function") apply​([T](../../../java/util/function/Function.html "type parameter in Function") t)  
     Applies this function to the given argument.  
     Parameters:  
     `t` \- the function argument  
     Returns:  
     the function result  
     * #### compose  
     default <V> [Function](../../../java/util/function/Function.html "interface in java.util.function")<V,[R](../../../java/util/function/Function.html "type parameter in Function")> compose​([Function](../../../java/util/function/Function.html "interface in java.util.function")<? super V,? extends [T](../../../java/util/function/Function.html "type parameter in Function")> before)  
     Returns a composed function that first applies the `before` function to its input, and then applies this function to the result. If evaluation of either function throws an exception, it is relayed to the caller of the composed function.  
     Type Parameters:  
     `V` \- the type of input to the `before` function, and to the composed function  
     Parameters:  
     `before` \- the function to apply before this function is applied  
     Returns:  
     a composed function that first applies the `before` function and then applies this function  
     Throws:  
     `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if before is null  
     See Also:  
     [andThen(Function)](../../../java/util/function/Function.html#andThen-java.util.function.Function-)  
     * #### andThen  
     default <V> [Function](../../../java/util/function/Function.html "interface in java.util.function")<[T](../../../java/util/function/Function.html "type parameter in Function"),V> andThen​([Function](../../../java/util/function/Function.html "interface in java.util.function")<? super [R](../../../java/util/function/Function.html "type parameter in Function"),? extends V> after)  
     Returns a composed function that first applies this function to its input, and then applies the `after` function to the result. If evaluation of either function throws an exception, it is relayed to the caller of the composed function.  
     Type Parameters:  
     `V` \- the type of output of the `after` function, and of the composed function  
     Parameters:  
     `after` \- the function to apply after this function is applied  
     Returns:  
     a composed function that first applies this function and then applies the `after` function  
     Throws:  
     `[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang")` \- if after is null  
     See Also:  
     [compose(Function)](../../../java/util/function/Function.html#compose-java.util.function.Function-)  
     * #### identity  
     static <T> [Function](../../../java/util/function/Function.html "interface in java.util.function")<T,T> identity​()  
     Returns a function that always returns its input argument.  
     Type Parameters:  
     `T` \- the type of the input and output objects to the function  
     Returns:  
     a function that always returns its input argument

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