Class SetOfUnknownSize<E>

Object
AbstractCollection<E>
AbstractSet<E>
SetOfUnknownSize<E>
Type Parameters:
E - the type of elements in the set.
All Implemented Interfaces:
Iterable<E>, Collection<E>, Set<E>
public abstract class SetOfUnknownSize<E> extends AbstractSet<E>
An alternative to Abstract­Set for implementations having a costly size() method. The size of the set is not known in advance, but may become known after one complete iteration. This class overrides methods in a way that reduces or eliminates the need to invoke size().

Note for implementers

Subclasses should implement the following methods:
Since:
1.6

  • Constructor Details

    • SetOfUnknownSize

      protected SetOfUnknownSize()
      Creates a new set of initially unknown size.

  • Method Details

    • isEmpty

      public boolean isEmpty()
      Returns true if this set is empty. The implementation of this method avoids to invoke size().
      Specified by:
      is­Empty in interface Collection<E>
      Specified by:
      is­Empty in interface Set<E>
      Overrides:
      is­Empty in class Abstract­Collection<E>
      Returns:
      true if this set is empty.

    • size

      public int size()
      Returns the number of elements in this set. The default implementation returns the size if known, or otherwise counts the number of elements returned by the iterator.
      Specified by:
      size in interface Collection<E>
      Specified by:
      size in interface Set<E>
      Specified by:
      size in class Abstract­Collection<E>
      Returns:
      the number of elements in this set.

    • sizeIfKnown

      protected OptionalInt sizeIfKnown()
      Returns the size() value if it is already known, or empty if the size is still unknown. The default implementation always returns an empty value. Subclasses can overwrite this method if they have already computed and cached the number of elements. When this information is known, some Set­Of­Unknown­Size methods will take a more efficient path.
      Returns:
      size() if its value is already known, or empty if this value is still costly to compute.

    • removeAll

      public boolean removeAll(Collection<?> c)
      Removes elements of the given collection from this set. The implementation of this method avoids to invoke size().
      Specified by:
      remove­All in interface Collection<E>
      Specified by:
      remove­All in interface Set<E>
      Overrides:
      remove­All in class Abstract­Set<E>
      Parameters:
      c - the collection containing elements to remove.
      Returns:
      true if at least one element has been removed.

    • characteristics

      protected int characteristics()
      Returns characteristics of this collection as a combination of Spliterator bits. The default implementation returns Spliterator​.DISTINCT. Subclasses should add the Spliterator​.NONNULL bit if they guarantee that this set does not contain the null element.
      Returns:
      the characteristics of this collection.
      See Also:

    • spliterator

      public Spliterator<E> spliterator()
      Creates a Spliterator which may be of unknown size.
      Returns:
      a Spliterator over the elements in this collection.

    • toArray

      public Object[] toArray()
      Returns all elements in an array. The implementation of this method avoids to invoke size().
      Specified by:
      to­Array in interface Collection<E>
      Specified by:
      to­Array in interface Set<E>
      Overrides:
      to­Array in class Abstract­Collection<E>
      Returns:
      an array containing all set elements.

    • toArray

      public <T> T[] toArray(T[] array)
      Returns the elements in the given array, or in a new array if it was necessary to allocate more space. If the given array is larger than necessary, the remaining array elements are set to null. The implementation of this method avoids to invoke size().
      Specified by:
      to­Array in interface Collection<E>
      Specified by:
      to­Array in interface Set<E>
      Overrides:
      to­Array in class Abstract­Collection<E>
      Type Parameters:
      T - the type array elements.
      Parameters:
      array - where to store the elements.
      Returns:
      an array containing all set elements.

    • toArray

      public <T> T[] toArray(IntFunction<T[]> generator)
      Returns the elements in an array generated by the given function. The implementation of this method avoids to invoke size().
      Type Parameters:
      T - the type array elements.
      Parameters:
      generator - the function for allocating a new array.
      Returns:
      an array containing all set elements.

    • equals

      public boolean equals(Object other)
      Returns true if the given object is also a set and the two sets have the same content. The implementation of this method avoids to invoke size() on this instance. However, it still call other​.size().
      Specified by:
      equals in interface Collection<E>
      Specified by:
      equals in interface Set<E>
      Overrides:
      equals in class Abstract­Set<E>
      Parameters:
      other - the object to compare with this set.
      Returns:
      true if the two set have the same content.