Package org.apache.commons.lang3.function

Class Functions

  • public final class Functions
extends java.lang.Object
    Factory for Function.
    Since:
    3.14.0

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      private Functions()  

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static <T,​R>
      R      		 apply​(java.util.function.Function<T,​R> function, T object)
      Applies the Function on the object if the function is not null.
      static <T,​R>
      R      		 applyNonNull​(T value, java.util.function.Function<? super T,​? extends R> mapper)
      Applies a value to a function if the value isn't null, otherwise the method returns null.
      static <T,​U,​R>
      R      		 applyNonNull​(T value1, java.util.function.Function<? super T,​? extends U> mapper1, java.util.function.Function<? super U,​? extends R> mapper2)
      Applies values to a chain of functions, where a null can short-circuit each step.
      static <T,​U,​V,​R>
      R      		 applyNonNull​(T value1, java.util.function.Function<? super T,​? extends U> mapper1, java.util.function.Function<? super U,​? extends V> mapper2, java.util.function.Function<? super V,​? extends R> mapper3)
      Applies values to a chain of functions, where a null can short-circuit each step.
      static <T,​R>
      java.util.function.Function<T,​R>      		 function​(java.util.function.Function<T,​R> function)
      Starts a fluent chain like function(foo::bar).andThen(...).andThen(...).apply(...);

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • Functions

        private Functions()

    • Method Detail

      • apply

        public static <T,​R> R apply​(java.util.function.Function<T,​R> function,
                                  T object)
        Applies the Function on the object if the function is not null. Otherwise, does nothing and returns null.
        Type Parameters:
        T - the type of the argument the function applies.
        R - the type of the result the function returns.
        Parameters:
        function - the function to apply.
        object - the object to apply the function.
        Returns:
        the value the function returns if the function is not null; null otherwise.
        Since:
        3.15.0

      • applyNonNull

        public static <T,​R> R applyNonNull​(T value,
                                         java.util.function.Function<? super T,​? extends R> mapper)
        Applies a value to a function if the value isn't null, otherwise the method returns null. If the value isn't null then return the result of the applying function. 
        
 Functions.applyNonNull("a", String::toUpperCase)  = "A"
 Functions.applyNonNull(null, String::toUpperCase) = null
 Functions.applyNonNull("a", s -> null)            = null

        Useful when working with expressions that may return null as it allows a single-line expression without using temporary local variables or evaluating expressions twice. Provides an alternative to using Optional that is shorter and has less allocation.

        Type Parameters:
        T - The type of the input of this method and the function.
        R - The type of the result of the function and this method.
        Parameters:
        value - The value to apply the function to, may be null.
        mapper - The function to apply, must not be null.
        Returns:
        The result of the function (which may be null) or null if the input value is null.
        Since:
        3.19.0
        See Also:
        applyNonNull(Object, Function, Function), applyNonNull(Object, Function, Function, Function)

      • applyNonNull

        public static <T,​U,​R> R applyNonNull​(T value1,
                                                 java.util.function.Function<? super T,​? extends U> mapper1,
                                                 java.util.function.Function<? super U,​? extends R> mapper2)
        Applies values to a chain of functions, where a null can short-circuit each step. A function is only applied if the previous value is not null, otherwise this method returns null. 
        
 Functions.applyNonNull(" a ", String::toUpperCase, String::trim) = "A"
 Functions.applyNonNull(null, String::toUpperCase, String::trim)  = null
 Functions.applyNonNull(" a ", s -> null, String::trim)           = null
 Functions.applyNonNull(" a ", String::toUpperCase, s -> null)    = null

        Useful when working with expressions that may return null as it allows a single-line expression without using temporary local variables or evaluating expressions twice. Provides an alternative to using Optional that is shorter and has less allocation.

        Type Parameters:
        T - The type of the input of this method and the first function.
        U - The type of the result of the first function and the input to the second function.
        R - The type of the result of the second function and this method.
        Parameters:
        value1 - The value to apply the functions to, may be null.
        mapper1 - The first function to apply, must not be null.
        mapper2 - The second function to apply, must not be null.
        Returns:
        The result of the final function (which may be null) or null if the input value or any intermediate value is null.
        Since:
        3.19.0
        See Also:
        applyNonNull(Object, Function), applyNonNull(Object, Function, Function, Function)

      • applyNonNull

        public static <T,​U,​V,​R> R applyNonNull​(T value1,
                                                         java.util.function.Function<? super T,​? extends U> mapper1,
                                                         java.util.function.Function<? super U,​? extends V> mapper2,
                                                         java.util.function.Function<? super V,​? extends R> mapper3)
        Applies values to a chain of functions, where a null can short-circuit each step. A function is only applied if the previous value is not null, otherwise this method returns null. 
        
 Functions.applyNonNull(" abc ", String::toUpperCase, String::trim, StringUtils::reverse) = "CBA"
 Functions.applyNonNull(null, String::toUpperCase, String::trim, StringUtils::reverse)    = null
 Functions.applyNonNull(" abc ", s -> null, String::trim, StringUtils::reverse)           = null
 Functions.applyNonNull(" abc ", String::toUpperCase, s -> null, StringUtils::reverse)    = null
 Functions.applyNonNull(" abc ", String::toUpperCase, String::trim, s -> null)            = null

        Useful when working with expressions that may return null as it allows a single-line expression without using temporary local variables or evaluating expressions twice. Provides an alternative to using Optional that is shorter and has less allocation.

        Type Parameters:
        T - The type of the input of this method and the first function.
        U - The type of the result of the first function and the input to the second function.
        V - The type of the result of the second function and the input to the third function.
        R - The type of the result of the third function and this method.
        Parameters:
        value1 - The value to apply the first function, may be null.
        mapper1 - The first function to apply, must not be null.
        mapper2 - The second function to apply, must not be null.
        mapper3 - The third function to apply, must not be null.
        Returns:
        The result of the final function (which may be null) or null if the input value or any intermediate value is null.
        Since:
        3.19.0
        See Also:
        applyNonNull(Object, Function), applyNonNull(Object, Function, Function)

      • function

        public static <T,​R> java.util.function.Function<T,​R> function​(java.util.function.Function<T,​R> function)
        Starts a fluent chain like function(foo::bar).andThen(...).andThen(...).apply(...);
        Type Parameters:
        T - Input type.
        R - Return type.
        Parameters:
        function - the argument to return.
        Returns:
        the argument