Class DescendingMultiset

guava/src/com/google/common/collect/DescendingMultiset.java:34–164

A skeleton implementation of a descending multiset. Only needs {@code forwardMultiset()} and {@code entryIterator()}. @author Louis Wasserman

 * @author Louis Wasserman
 */
@GwtCompatible
abstract class DescendingMultiset<E extends @Nullable Object> extends ForwardingMultiset<E>
    implements SortedMultiset<E> {
  abstract SortedMultiset<E> forwardMultiset();

  @LazyInit private transient @Nullable Comparator<? super E> comparator;

  @Override
  public Comparator<? super E> comparator() {
    Comparator<? super E> result = comparator;
    if (result == null) {
      result = Ordering.from(forwardMultiset().comparator()).reverse();
      comparator = result;
    }
    return result;
  }

  @LazyInit private transient @Nullable NavigableSet<E> elementSet;

  @Override
  public NavigableSet<E> elementSet() {
    NavigableSet<E> result = elementSet;
    if (result == null) {
      return elementSet = new SortedMultisets.NavigableElementSet<>(this);
    }
    return result;
  }

  @Override
  public @Nullable Entry<E> pollFirstEntry() {
    return forwardMultiset().pollLastEntry();
  }

  @Override
  public @Nullable Entry<E> pollLastEntry() {
    return forwardMultiset().pollFirstEntry();
  }

  @Override
  public SortedMultiset<E> headMultiset(@ParametricNullness E toElement, BoundType boundType) {
    return forwardMultiset().tailMultiset(toElement, boundType).descendingMultiset();
  }

  @Override
  public SortedMultiset<E> subMultiset(
      @ParametricNullness E fromElement,
      BoundType fromBoundType,
      @ParametricNullness E toElement,
      BoundType toBoundType) {
    return forwardMultiset()
        .subMultiset(toElement, toBoundType, fromElement, fromBoundType)
        .descendingMultiset();
  }

  @Override
  public SortedMultiset<E> tailMultiset(@ParametricNullness E fromElement, BoundType boundType) {
    return forwardMultiset().headMultiset(fromElement, boundType).descendingMultiset();
  }