Package org.kiwiproject.collect

Class KiwiLists

  • public class KiwiLists
extends Object
    Utility methods for working with List instances.

    • Constructor Summary

      Constructors 
      Constructor Description
      KiwiLists()  

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static <T> void checkMinimumSize​(List<T> items, int minSize)
      Checks that the given list is not null and has the given minimum size.
      static <T> void checkNonNullInputList​(List<T> items)
      Checks that the given list is not null.
      static <T> List<T> distinct​(Collection<T> collection)
      Returns a list of the collection elements with duplicates stripped out.
      static <T> List<T> distinctOrNull​(Collection<T> collection)
      Returns a list of the collection elements with duplicates stripped out or `null` if a null value is passed in.
      static <T> T fifth​(List<T> items)
      Return the fifth element in the specified list of items.
      static <T> T first​(List<T> items)
      Return the first element in the specified list of items.
      static <T> Optional<T> firstIfPresent​(List<T> items)
      Returns an Optional containing the first element in specified list of items, or an empty optional if the list is null or empty.
      static <T> List<T> firstN​(List<T> items, int number)
      Returns a view of the "first N" elements of the input list.
      static <T> T fourth​(List<T> items)
      Return the fourth element in the specified list of items.
      static <T> boolean hasOneElement​(List<T> items)
      Checks whether the specified list is non-null and has only one item.
      static <T> boolean isNotNullOrEmpty​(List<T> items)
      Checks whether the specified list is neither null nor empty.
      static <T> boolean isNullOrEmpty​(List<T> items)
      Checks whether the specified list is null or empty.
      static <T> T last​(List<T> items)
      Returns the last element in the specified list of items.
      static <T> Optional<T> lastIfPresent​(List<T> items)
      Returns an Optional containing the last element in specified list of items, or an empty optional if the list is null or empty.
      static <T> List<T> lastN​(List<T> items, int number)
      Returns a view of the "last N" elements of the input list.
      static <T> List<T> newListStartingAtCircularOffset​(List<T> input, long startOffset)
      Returns a new list with the same elements and the same size as the original, however the initial position in the list is now the element specified by the "startOffset" and the list wraps around through the contents to end with "startOffset" - 1
      static <T> T nth​(List<T> items, int number)
      Return the nth element in the specified list of items, starting at one for the first element, two for the second, etc.
      static <T> T penultimate​(List<T> items)
      Returns the penultimate (second to last) element in the specified list.
      static <T> T second​(List<T> items)
      Return the second element in the specified list of items.
      static <T> T secondToLast​(List<T> items)
      Synonym for penultimate(List).
      static <T> List<T> shuffledArrayListOf​(T... items)
      Create a new ArrayList with the given items shuffled using Collections.shuffle(List).
      static <T> List<T> shuffledListOf​(T... items)
      Create a new unmodifiable List with the given items shuffled using Collections.shuffle(List).
      static <T> List<T> sorted​(List<T> items)
      Given a list, sort it according to the natural order, returning a new list.
      static <T> List<T> sorted​(List<T> items, Comparator<T> comparator)
      Given a list, sort it according to the provided Comparator returning a new list.
      static <T> List<T> subListExcludingFirst​(List<T> items)
      Returns a view of the portion of the given list excluding the first element.
      static <T> List<T> subListExcludingLast​(List<T> items)
      Returns a view of the portion of the given list excluding the last element.
      static <T> List<T> subListFrom​(List<T> items, int number)
      Returns a view of the portion of the given list starting at the given logical element number, where the numbers start at one, until and including the last element in the list.
      static <T> List<T> subListFromIndex​(List<T> items, int index)
      Returns a view of the portion of the given list starting at the given index, until and including the last element in the list.
      static <T> T third​(List<T> items)
      Return the third element in the specified list of items.

    • Constructor Detail

      • KiwiLists

        public KiwiLists()

    • Method Detail

      • isNullOrEmpty

        public static <T> boolean isNullOrEmpty​(List<T> items)
        Checks whether the specified list is null or empty.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        true if list is null or empty; false otherwise

      • isNotNullOrEmpty

        public static <T> boolean isNotNullOrEmpty​(List<T> items)
        Checks whether the specified list is neither null nor empty.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        true if list is NOT null or empty; false otherwise

      • hasOneElement

        public static <T> boolean hasOneElement​(List<T> items)
        Checks whether the specified list is non-null and has only one item.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        true if list is non-null and has exactly one item; false otherwise

      • sorted

        public static <T> List<T> sorted​(List<T> items)
        Given a list, sort it according to the natural order, returning a new list.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        a new sorted list

      • sorted

        public static <T> List<T> sorted​(List<T> items,
                                 Comparator<T> comparator)
        Given a list, sort it according to the provided Comparator returning a new list.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        comparator - a Comparator to be used to compare stream elements
        Returns:
        a new sorted list

      • first

        public static <T> T first​(List<T> items)
        Return the first element in the specified list of items.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        the first item in items
        Throws:
        IllegalArgumentException - if the list does not contain at least one item
        NullPointerException - if the list is null

      • firstIfPresent

        public static <T> Optional<T> firstIfPresent​(List<T> items)
        Returns an Optional containing the first element in specified list of items, or an empty optional if the list is null or empty.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        Optional containing first element if exists, otherwise Optional.empty()

      • second

        public static <T> T second​(List<T> items)
        Return the second element in the specified list of items.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        the second item in items
        Throws:
        IllegalArgumentException - if the list does not contain at least two items
        NullPointerException - if the list is null

      • third

        public static <T> T third​(List<T> items)
        Return the third element in the specified list of items.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        the third item in items
        Throws:
        IllegalArgumentException - if the list does not contain at least three items
        NullPointerException - if the list is null

      • fourth

        public static <T> T fourth​(List<T> items)
        Return the fourth element in the specified list of items.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        the fourth item in items
        Throws:
        IllegalArgumentException - if the list does not contain at least four items
        NullPointerException - if the list is null

      • fifth

        public static <T> T fifth​(List<T> items)
        Return the fifth element in the specified list of items.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        the fifth item in items
        Throws:
        IllegalArgumentException - if the list does not contain at least five items
        NullPointerException - if the list is null

      • penultimate

        public static <T> T penultimate​(List<T> items)
        Returns the penultimate (second to last) element in the specified list.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        the penultimate item in items
        Throws:
        IllegalArgumentException - if the list does not contain at least two items
        NullPointerException - if the list is null
        See Also:
        secondToLast(List)

      • last

        public static <T> T last​(List<T> items)
        Returns the last element in the specified list of items.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        the last item in the list
        Throws:
        IllegalArgumentException - if the list does not contain at least one item
        NullPointerException - if the list is null

      • lastIfPresent

        public static <T> Optional<T> lastIfPresent​(List<T> items)
        Returns an Optional containing the last element in specified list of items, or an empty optional if the list is null or empty.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        Returns:
        Optional containing last element if exists, otherwise Optional.empty()

      • nth

        public static <T> T nth​(List<T> items,
                        int number)
        Return the nth element in the specified list of items, starting at one for the first element, two for the second, etc.
        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        number - the number of the element to retrieve, starting at one (not zero)
        Returns:
        the nth item in items
        Throws:
        IllegalArgumentException - if the list does not contain at least number items
        NullPointerException - if the list is null

      • distinct

        public static <T> List<T> distinct​(Collection<T> collection)
        Returns a list of the collection elements with duplicates stripped out.
        Type Parameters:
        T - the type of items in the collection
        Parameters:
        collection - the collection of values
        Returns:
        a new list with only unique elements
        Throws:
        IllegalArgumentException - if the collection is null

      • distinctOrNull

        public static <T> List<T> distinctOrNull​(Collection<T> collection)
        Returns a list of the collection elements with duplicates stripped out or `null` if a null value is passed in.
        Type Parameters:
        T - the type of items in the collection
        Parameters:
        collection - the collection of values
        Returns:
        a new list with only unique elements or null.

      • newListStartingAtCircularOffset

        public static <T> List<T> newListStartingAtCircularOffset​(List<T> input,
                                                          long startOffset)
        Returns a new list with the same elements and the same size as the original, however the initial position in the list is now the element specified by the "startOffset" and the list wraps around through the contents to end with "startOffset" - 1
        Type Parameters:
        T - the type of the items in the list
        Parameters:
        input - the original list
        startOffset - the desired offset to start the new list
        Returns:
        a new list starting at the desired offset

      • subListExcludingFirst

        public static <T> List<T> subListExcludingFirst​(List<T> items)
        Returns a view of the portion of the given list excluding the first element.

        This method has the same semantics as List.subList(int, int) since it calls that method.

        Type Parameters:
        T - the type of the items in the list
        Parameters:
        items - the list
        Returns:
        a view of the given list excluding the first item backed by the original list
        Throws:
        NullPointerException - if the list is null
        See Also:
        List.subList(int, int)

      • subListExcludingLast

        public static <T> List<T> subListExcludingLast​(List<T> items)
        Returns a view of the portion of the given list excluding the last element.

        This method has the same semantics as List.subList(int, int) since it calls that method.

        Type Parameters:
        T - the type of the items in the list
        Parameters:
        items - the list
        Returns:
        a view of the given list excluding the last item backed by the original list
        Throws:
        NullPointerException - if the list is null
        See Also:
        List.subList(int, int)

      • subListFrom

        public static <T> List<T> subListFrom​(List<T> items,
                                      int number)
        Returns a view of the portion of the given list starting at the given logical element number, where the numbers start at one, until and including the last element in the list. This is useful if something is using one-based element numbers for some reason. Use subListFromIndex(List, int) if you want to use zero-based list indices.

        This method has the same semantics as List.subList(int, int) since it calls that method.

        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        number - the number of the element to start the sublist, starting at one (not zero)
        Returns:
        a view of the given list backed by the original list, starting at the given one-based number
        Throws:
        NullPointerException - if the list is null
        IllegalArgumentException - if the given number is negative or is higher than the size of the list
        See Also:
        List.subList(int, int)

      • subListFromIndex

        public static <T> List<T> subListFromIndex​(List<T> items,
                                           int index)
        Returns a view of the portion of the given list starting at the given index, until and including the last element in the list.

        This method has the same semantics as List.subList(int, int) since it calls that method.

        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        index - the index in the list to start the sublist, zero-based like normal List methods
        Returns:
        a view of the given list backed by the original list, starting at the given zero-based index
        Throws:
        NullPointerException - if the list is null
        IllegalArgumentException - if the given index is negative or is higher than the last index in the list
        See Also:
        List.subList(int, int)

      • firstN

        public static <T> List<T> firstN​(List<T> items,
                                 int number)
        Returns a view of the "first N" elements of the input list.

        If the given number is larger than the size of the list, the entire list is returned, rather than throw an exception. In this case, the input list is returned directly, i.e. return items.

        This method has the same semantics as List.subList(int, int) since it calls that method.

        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        number - the number of items wanted from the start of the list
        Returns:
        a view of the given list, backed by the original list, containing the last number elements
        See Also:
        List.subList(int, int)

      • lastN

        public static <T> List<T> lastN​(List<T> items,
                                int number)
        Returns a view of the "last N" elements of the input list.

        If the given number is larger than the size of the list, the entire list is returned, rather than throw an exception. In this case, the input list is returned directly, i.e. return items.

        This method has the same semantics as List.subList(int, int) since it calls that method.

        Type Parameters:
        T - the type of items in the list
        Parameters:
        items - the list
        number - the number of items wanted from the end of the list
        Returns:
        a view of the given list, backed by the original list, containing the first number elements
        See Also:
        List.subList(int, int)

      • checkMinimumSize

        public static <T> void checkMinimumSize​(List<T> items,
                                        int minSize)
        Checks that the given list is not null and has the given minimum size.
        Type Parameters:
        T - the type of the items in the list
        Parameters:
        items - the list
        minSize - the minimum required size
        Throws:
        NullPointerException - if the list is null
        IllegalArgumentException - if minSize is not positive or the list does not contain minSize elements

      • checkNonNullInputList

        public static <T> void checkNonNullInputList​(List<T> items)
        Checks that the given list is not null.
        Type Parameters:
        T - the type of the items in the list
        Parameters:
        items - the list
        Throws:
        NullPointerException - if the list is null

      • shuffledListOf

        @SafeVarargs
public static <T> List<T> shuffledListOf​(T... items)
        Create a new unmodifiable List with the given items shuffled using Collections.shuffle(List).
        Type Parameters:
        T - the type of the items in the list
        Parameters:
        items - the items to include in the new list
        Returns:
        an unmodifiable List with the given items in pseudorandom order

      • shuffledArrayListOf

        @SafeVarargs
public static <T> List<T> shuffledArrayListOf​(T... items)
        Create a new ArrayList with the given items shuffled using Collections.shuffle(List).
        Type Parameters:
        T - the type of the items in the list
        Parameters:
        items - the items to include in the new list
        Returns:
        an ArrayList with the given items in pseudorandom order