Interface Function1<T1,R>

Type Parameters:
T1 - argument 1 of the function
R - return type of the function
All Superinterfaces:
Function<T1,R>, Serializable
All Known Subinterfaces:
API.Match.Case<T,R>, API.Match.Pattern<T,R>, BitSet<T>, IndexedSeq<T>, LinearSeq<T>, List<T>, Map<K,V>, Multimap<K,V>, PartialFunction<T,R>, Seq<T>, Set<T>, SortedMap<K,V>, SortedMultimap<K,V>, SortedSet<T>, Stream<T>
All Known Implementing Classes:
AbstractMultimap, API.Match.Case0, API.Match.Case1, API.Match.Case2, API.Match.Case3, API.Match.Case4, API.Match.Case5, API.Match.Case6, API.Match.Case7, API.Match.Case8, API.Match.Pattern0, API.Match.Pattern1, API.Match.Pattern2, API.Match.Pattern3, API.Match.Pattern4, API.Match.Pattern5, API.Match.Pattern6, API.Match.Pattern7, API.Match.Pattern8, Array, BitSetModule.AbstractBitSet, BitSetModule.BitSet1, BitSetModule.BitSet2, BitSetModule.BitSetN, CharSeq, HashMap, HashMultimap, HashSet, LinkedHashMap, LinkedHashMultimap, LinkedHashSet, List.Cons, List.Nil, Queue, Stream.Cons, Stream.Empty, StreamModule.AppendElements, StreamModule.ConsImpl, TreeMap, TreeMultimap, TreeSet, Vector
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 Function1<T1,R> extends Serializable, Function<T1,R>
Represents a function with one argument.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final long
    serialVersionUID
    The serial version uid.

  • Method Summary

    Modifier and Type
    Method
    Description
    default <V> Function1<T1,V>
    andThen(Function<? super R, ? extends V> after)
    Returns a composed function that first applies this Function1 to the given argument and then applies Function after to the result.
    R
    apply(T1 t1)
    Applies this function to one argument and returns the result.
    default int
    arity()
    Returns the number of function arguments.
    default <V> Function1<V,R>
    compose(Function<? super V, ? extends T1> before)
    Returns a composed function that first applies the Function before the given argument and then applies this Function1 to the result.
    static <T1,R> Function1<T1,R>
    constant(R value)
    Returns a function that always returns the constant value that you give in parameter.
    default Function1<T1,R>
    curried()
    Returns a curried version of this function.
    static <T> Function1<T,T>
    identity()
    Returns the identity Function1, i.e.
    default boolean
    isMemoized()
    Checks if this function is memoizing (= caching) computed values.
    static <T1,R> Function1<T1, Option<R>>
    lift(Function<? super T1, ? extends R> partialFunction)
    Lifts the given partialFunction into a total function that returns an Option result.
    static <T1,R> Function1<T1,Try<R>>
    liftTry(Function<? super T1, ? extends R> partialFunction)
    Lifts the given partialFunction into a total function that returns an Try result.
    default Function1<T1,R>
    memoized()
    Returns a memoizing version of this function, which computes the return value for given arguments only one time.
    static <T1,R> Function1<T1,R>
    narrow(Function1<? super T1, ? extends R> f)
    Narrows the given Function1<? super T1, ? extends R> to Function1<T1, R>
    static <T1,R> Function1<T1,R>
    of(Function1<T1,R> methodReference)
    Creates a Function1 based on method reference lambda expression Examples (w.l.o.g.
    default PartialFunction<T1,R>
    partial(Predicate<? super T1> isDefinedAt)
    Converts this Function1 to a PartialFunction by adding an isDefinedAt condition.
    default Function1<T1,R>
    reversed()
    Returns a reversed version of this function.
    default Function1<Tuple1<T1>, R>
    tupled()
    Returns a tupled version of this function.

  • Field Details

  • Method Details

    • constant

      static <T1,R> Function1<T1,R> constant(R value)
      Returns a function that always returns the constant value that you give in parameter.
      Type Parameters:
      T1 - generic parameter type 1 of the resulting function
      R - the result type
      Parameters:
      value - the value to be returned
      Returns:
      a function always returning the given value

    • of

      static <T1,R> Function1<T1,R> of(Function1<T1,R> methodReference)
      Creates a Function1 based on Examples (w.l.o.g. referring to Function1): 
      // using a lambda expression
Function1<Integer, Integer> add1 = Function1.of(i -> i + 1);

// using a method reference (, e.g. Integer method(Integer i) { return i + 1; })
Function1<Integer, Integer> add2 = Function1.of(this::method);

// using a lambda reference
Function1<Integer, Integer> add3 = Function1.of(add1::apply);

      Caution: Reflection loses type information of lambda references. 

      // type of a lambda expression
Type<?, ?> type1 = add1.getType(); // (Integer) -> Integer

// type of a method reference
Type<?, ?> type2 = add2.getType(); // (Integer) -> Integer

// type of a lambda reference
Type<?, ?> type3 = add3.getType(); // (Object) -> Object
      Type Parameters:
      T1 - 1st argument
      R - return type
      Parameters:
      methodReference - (typically) a method reference, e.g. Type::method
      Returns:
      a Function1

    • lift

      static <T1,R> Function1<T1, Option<R>> lift(Function<? super T1, ? extends R> partialFunction)
      Lifts the given partialFunction into a total function that returns an Option result.
      Type Parameters:
      T1 - 1st argument
      R - return type
      Parameters:
      partialFunction - a function that is not defined for all values of the domain (e.g. by throwing)
      Returns:
      a function that applies arguments to the given partialFunction and returns Some(result) if the function is defined for the given arguments, and None otherwise.

    • liftTry

      static <T1,R> Function1<T1,Try<R>> liftTry(Function<? super T1, ? extends R> partialFunction)
      Lifts the given partialFunction into a total function that returns an Try result.
      Type Parameters:
      T1 - 1st argument
      R - return type
      Parameters:
      partialFunction - a function that is not defined for all values of the domain (e.g. by throwing)
      Returns:
      a function that applies arguments to the given partialFunction and returns Success(result) if the function is defined for the given arguments, and Failure(throwable) otherwise.

    • narrow

      static <T1,R> Function1<T1,R> narrow(Function1<? super T1, ? extends R> f)
      Narrows the given Function1<? super T1, ? extends R> to Function1<T1, R>
      Type Parameters:
      T1 - 1st argument
      R - return type
      Parameters:
      f - A Function1
      Returns:
      the given f instance as narrowed type Function1<T1, R>

    • identity

      static <T> Function1<T,T> identity()
      Returns the identity Function1, i.e. the function that returns its input.
      Type Parameters:
      T - argument type (and return type) of the identity function
      Returns:
      the identity Function1

    • apply

      R apply(T1 t1)
      Applies this function to one argument and returns the result.
      Specified by:
      apply in interface Function<T1,R>
      Parameters:
      t1 - argument 1
      Returns:
      the result of function application

    • arity

      default int arity()
      Returns the number of function arguments.
      Returns:
      an int value >= 0
      See Also:

    • curried

      default Function1<T1,R> curried()
      Returns a curried version of this function.
      Returns:
      a curried function equivalent to this.

    • tupled

      default Function1<Tuple1<T1>, R> tupled()
      Returns a tupled version of this function.
      Returns:
      a tupled function equivalent to this.

    • reversed

      default Function1<T1,R> reversed()
      Returns a reversed version of this function. This may be useful in a recursive context.
      Returns:
      a reversed function equivalent to this.

    • memoized

      default Function1<T1,R> memoized()
      Returns a memoizing version of this function, which computes the return value for given arguments only one time. On subsequent calls given the same arguments the memoized value is returned.

      Please note that memoizing functions do not permit null as single argument or return value.

      Returns:
      a memoizing function equivalent to this.

    • isMemoized

      default boolean isMemoized()
      Checks if this function is memoizing (= caching) computed values.
      Returns:
      true, if this function is memoizing, false otherwise

    • partial

      default PartialFunction<T1,R> partial(Predicate<? super T1> isDefinedAt)
      Converts this Function1 to a PartialFunction by adding an isDefinedAt condition.

      Parameters:
      isDefinedAt - a predicate that states if an element is in the domain of the returned PartialFunction.
      Returns:
      a new PartialFunction that has the same behavior like this function but is defined only for those elements that make it through the given Predicate
      Throws:
      NullPointerException - if isDefinedAt is null

    • andThen

      default <V> Function1<T1,V> andThen(Function<? super R, ? extends V> after)
      Returns a composed function that first applies this Function1 to the given argument and then applies Function after to the result.
      Specified by:
      andThen in interface Function<T1,R>
      Type Parameters:
      V - return type of after
      Parameters:
      after - the function applied after this
      Returns:
      a function composed of this and after
      Throws:
      NullPointerException - if after is null

    • compose

      default <V> Function1<V,R> compose(Function<? super V, ? extends T1> before)
      Returns a composed function that first applies the Function before the given argument and then applies this Function1 to the result.
      Specified by:
      compose in interface Function<T1,R>
      Type Parameters:
      V - argument type of before
      Parameters:
      before - the function applied before this
      Returns:
      a function composed of before and this
      Throws:
      NullPointerException - if before is null