Package org.apache.calcite.linq4j.function

Class Functions

java.lang.Object
org.apache.calcite.linq4j.function.Functions
public abstract class Functions extends Object
Utilities relating to functions.

  • Field Details

  • Method Details

    • constant

      public static <T, R> Function1<T,R> constant(R r)
      Returns a 1-parameter function that always returns the same value.

    • constantNull

      public static <T, R> Function1<T,R> constantNull()
      Returns a 1-parameter function that always returns null.

    • truePredicate1

      public static <T> Predicate1<T> truePredicate1()
      A predicate with one parameter that always returns true.
      Type Parameters:
      T - First parameter type
      Returns:
      Predicate that always returns true

    • falsePredicate1

      public static <T> Predicate1<T> falsePredicate1()
      A predicate with one parameter that always returns true.
      Type Parameters:
      T - First parameter type
      Returns:
      Predicate that always returns true

    • truePredicate2

      public static <T1, T2> Predicate2<T1,T2> truePredicate2()
      A predicate with two parameters that always returns true.
      Type Parameters:
      T1 - First parameter type
      T2 - Second parameter type
      Returns:
      Predicate that always returns true

    • falsePredicate2

      public static <T1, T2> Predicate2<T1,T2> falsePredicate2()
      A predicate with two parameters that always returns false.
      Type Parameters:
      T1 - First parameter type
      T2 - Second parameter type
      Returns:
      Predicate that always returns false

    • identitySelector

      public static <TSource> Function1<TSource,TSource> identitySelector()

    • toStringSelector

      public static <TSource> Function1<TSource,String> toStringSelector()
      Returns a selector that calls the Object.toString() method on each element.

    • ofTypePredicate

      public static <T, T2> Predicate1<T> ofTypePredicate(Class<T2> clazz)
      Creates a predicate that returns whether an object is an instance of a particular type or is null.
      Type Parameters:
      T - Type of objects to test
      T2 - Desired type
      Parameters:
      clazz - Desired type
      Returns:
      Predicate that tests for desired type

    • toPredicate2

      public static <T1, T2> Predicate2<T1,T2> toPredicate2(Predicate1<T1> p1)

    • toPredicate

      public static <T1, T2> Predicate2<T1,T2> toPredicate(Function2<T1,T2,Boolean> function)
      Converts a 2-parameter function to a predicate.

    • functionClass

      public static Class<? extends Function> functionClass(Type aClass)
      Returns the appropriate interface for a lambda function with 1 argument and the given return type.

      For example: functionClass(Integer.TYPE) returns IntegerFunction1.class; functionClass(String.class) returns Function1.class.

      Parameters:
      aClass - Return type
      Returns:
      Function class

    • adapt

      public static <T1> Function1<T1,Integer> adapt(IntegerFunction1<T1> f)
      Adapts an IntegerFunction1 (that returns an int) to an Function1 returning an Integer.

    • adapt

      public static <T1> Function1<T1,Double> adapt(DoubleFunction1<T1> f)
      Adapts a DoubleFunction1 (that returns a double) to an Function1 returning a Double.

    • adapt

      public static <T1> Function1<T1,Long> adapt(LongFunction1<T1> f)
      Adapts a LongFunction1 (that returns a long) to an Function1 returning a Long.

    • adapt

      public static <T1> Function1<T1,Float> adapt(FloatFunction1<T1> f)
      Adapts a FloatFunction1 (that returns a float) to an Function1 returning a Float.

    • adapt

      @Deprecated public static <T1, R> List<R> adapt(List<T1> list, Function1<T1,R> f)
      Deprecated.
      Use Lists.transform(java.util.List<F>, com.google.common.base.Function<? super F, ? extends T>)
      Creates a view of a list that applies a function to each element.

    • adapt

      @Deprecated public static <T, R> List<R> adapt(T[] ts, Function1<T,R> f)
      Deprecated.
      Use Lists.transform(java.util.List<F>, com.google.common.base.Function<? super F, ? extends T>) and Arrays.asList(Object[])
      Creates a view of an array that applies a function to each element.

    • apply

      public static <T1, R> List<R> apply(List<T1> list, Function1<T1,R> f)
      Creates a copy of a list, applying a function to each element.

    • filter

      public static <E> List<E> filter(List<E> list, Predicate1<E> predicate)
      Returns a list that contains only elements of list that match predicate. Avoids allocating a list if all elements match or no elements match.

    • exists

      public static <E> boolean exists(List<? extends E> list, Predicate1<E> predicate)
      Returns whether there is an element in list for which predicate is true.

    • all

      public static <E> boolean all(List<? extends E> list, Predicate1<E> predicate)
      Returns whether predicate is true for all elements of list.

    • generate

      public static <E> List<E> generate(int size, IntFunction<E> fn)
      Returns a list generated by applying a function to each index between 0 and size - 1.

    • ignore0

      public static <R> Function0<R> ignore0()
      Returns a function of arity 0 that does nothing.
      Type Parameters:
      R - Return type
      Returns:
      Function that does nothing.

    • ignore1

      public static <R, T0> Function1<R,T0> ignore1()
      Returns a function of arity 1 that does nothing.
      Type Parameters:
      R - Return type
      T0 - Type of parameter 0
      Returns:
      Function that does nothing.

    • ignore2

      public static <R, T0, T1> Function2<R,T0,T1> ignore2()
      Returns a function of arity 2 that does nothing.
      Type Parameters:
      R - Return type
      T0 - Type of parameter 0
      T1 - Type of parameter 1
      Returns:
      Function that does nothing.

    • nullsComparator

      public static <T extends Comparable<T>> Comparator<T> nullsComparator(boolean nullsFirst, boolean reverse)
      Returns a Comparator that handles null values.
      Parameters:
      nullsFirst - Whether nulls come before all other values
      reverse - Whether to reverse the usual order of Comparables

    • nullsComparator

      public static <T extends Comparable<T>> Comparator<T> nullsComparator(boolean nullsFirst, boolean reverse, Comparator<T> comparator)
      Returns a Comparator that handles null values.
      Parameters:
      nullsFirst - Whether nulls come before all other values
      reverse - Whether to reverse the usual order of Comparables
      comparator - Comparator to be used for comparison

    • identityComparer

      public static <T> EqualityComparer<T> identityComparer()
      Returns an EqualityComparer that uses object identity and hash code.

    • arrayComparer

      public static <T> EqualityComparer<T[]> arrayComparer()
      Returns an EqualityComparer that works on arrays of objects.

    • selectorComparer

      public static <T, T2> EqualityComparer<T> selectorComparer(Function1<T,T2> selector)
      Returns an EqualityComparer that uses a selector function.