Package com.pnfsoftware.jeb.util.collect

Class CollectionUtil

java.lang.Object
com.pnfsoftware.jeb.util.collect.CollectionUtil
public class CollectionUtil extends Object
Convenience methods for Java collections, in particular, lists.

  • Method Details

    • containsNull

      public static boolean containsNull(Iterable<?> c)
      Determine if the given iterable contains one or more null elements.
      Parameters:
      c - iterable to inspect
      Returns:
      true if at least one element is null

    • containsNonNull

      public static boolean containsNonNull(Iterable<?> c)
      Determine if the given iterable contains one or more non-null elements.
      Parameters:
      c - iterable to inspect
      Returns:
      true if at least one element is not null

    • containsReference

      public static <T> boolean containsReference(Collection<? extends T> c, T o)
      Determine if the collection contains the object reference (differs from Collection.contains(Object) by checking reference equality == instead of Object.equals(Object) equality)
      Type Parameters:
      T - element type
      Parameters:
      c - collection to loop into
      o - element whose presence in this collection is to be tested
      Returns:
      true if the collection contains the specified element

    • contains

      public static boolean contains(Collection<?> c, Object v)
      Safely check if an object is present within a collection.
      Parameters:
      c - collection, potentially null
      v - object, potentially null
      Returns:
      true IFF the object is contained in the collection

    • intersect

      public static <T> Set<T> intersect(Collection<? extends T> c1, Collection<? extends T> c2)
      Return the intersection of 2 collections (order of collection parameters does not matter).
      Type Parameters:
      T - element type
      Parameters:
      c1 - first collection
      c2 - second collection
      Returns:
      a set of intersection

    • hasIntersection

      public static <T> boolean hasIntersection(Collection<? extends T> c1, Collection<? extends T> c2)
      Determine whether two collections share at least one element.
      Type Parameters:
      T - element type
      Parameters:
      c1 - first collection
      c2 - second collection
      Returns:
      true if both collections contain at least one equal element

    • binarySearch

      public static <T, K extends Comparable<K>> T binarySearch(List<T> list, K key, IExtractor<T,K> extractor)
      Perform a binary search in an ordered list.
      Type Parameters:
      T - element type
      K - key type
      Parameters:
      list - a list of ordered items
      key - the ordering key for the items.
      extractor - key extractor
      Returns:
      the element, null if not found

    • binarySearchEx

      public static <T, K extends Comparable<K>> int binarySearchEx(List<? extends T> list, K key, IExtractor<T,? extends K> extractor, Comparator<K> cc)
      Perform a binary search in an ordered list.
      Type Parameters:
      T - element type
      K - key type
      Parameters:
      list - a list of ordered items
      key - the ordering key for the items.
      extractor - key extractor
      cc - optional custom comparator for the keys
      Returns:
      the zero+ index of the found element; else, the negative insertion index of the ghost element

    • compareByReference

      public static <T> boolean compareByReference(Collection<? extends T> c1, Collection<? extends T> c2, boolean sorted)
      Compare two collections using reference identity for elements.
      Type Parameters:
      T - element type
      Parameters:
      c1 - first collection
      c2 - second collection
      sorted - true if iteration order must be considered
      Returns:
      true if the collections contain the same references

    • compare

      public static <T> boolean compare(Collection<? extends T> c1, Collection<? extends T> c2, boolean sorted)
      Compare two collections using element equality.
      Type Parameters:
      T - element type
      Parameters:
      c1 - first collection
      c2 - second collection
      sorted - true if iteration order must be considered
      Returns:
      true if the collections contain the same elements

    • count

      public static <T> int count(Collection<T> coll, T item)
      Count elements using Object.equals(Object).
      Type Parameters:
      T - element type
      Parameters:
      coll - collection to inspect
      item - item to count
      Returns:
      number of equal elements

    • identityCount

      public static <T> int identityCount(Collection<T> coll, T item)
      Count elements using ==.
      Type Parameters:
      T - element type
      Parameters:
      coll - collection to inspect
      item - item to count
      Returns:
      number of identical elements

    • addNonNulls

      public static <T> Collection<T> addNonNulls(Collection<T> dst, Collection<? extends T> src)
      Add all non-null source elements to a destination collection.
      Type Parameters:
      T - element type
      Parameters:
      dst - destination collection
      src - optional source collection
      Returns:
      the destination collection

    • addNonNulls

      @SafeVarargs public static <T> Collection<T> addNonNulls(Collection<T> dst, T... elts)
      Add all non-null elements to a destination collection.
      Type Parameters:
      T - element type
      Parameters:
      dst - destination collection
      elts - optional elements
      Returns:
      the destination collection

    • doubleCollectionIterable

      public static <T> Iterable<T> doubleCollectionIterable(Collection<T> coll1, Collection<T> coll2)
      Create a generator that will iterate over two collections, starting with the first one, then the second one.

      This method is convenient to iterate over two collections without having to create an intermediate list holding the elements.

      Type Parameters:
      T - element type
      Parameters:
      coll1 - first collection
      coll2 - second collection
      Returns:
      an iterable

    • first

      public static <T> T first(Collection<T> coll)
      Retrieve the first item of a Collection. This method is safe and returns null if the collection is null or empty.
      Type Parameters:
      T - element type
      Parameters:
      coll - a collection
      Returns:
      the first item or null if collection is null or empty

    • last

      public static <T> T last(Collection<T> coll)
      Retrieve the last item of a Collection. This method is safe and returns null if the collection is null or empty.
      Type Parameters:
      T - element type
      Parameters:
      coll - a collection
      Returns:
      the last item or null if collection is null or empty