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Java example source code file (DescendingMultiset.java)

This example Java source code file (DescendingMultiset.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

boundtype, comparator, descendingmultiset, entry, forwardingmultiset, gwtcompatible, iterator, object, override, set, sortedmultiset, sortedset, string, util

The DescendingMultiset.java Java example source code

/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;

import java.util.Comparator;
import java.util.Iterator;
import java.util.Set;
import java.util.SortedSet;

/**
 * A skeleton implementation of a descending multiset.  Only needs
 * {@code forwardMultiset()} and {@code entryIterator()}.
 *
 * @author Louis Wasserman
 */
@GwtCompatible(emulated = true)
abstract class DescendingMultiset<E> extends ForwardingMultiset
    implements SortedMultiset<E> {
  abstract SortedMultiset<E> forwardMultiset();

  private transient Comparator<? super E> comparator;

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

  private transient SortedSet<E> elementSet;

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

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

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

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

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

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

  @Override protected Multiset<E> delegate() {
    return forwardMultiset();
  }

  @Override public SortedMultiset<E> descendingMultiset() {
    return forwardMultiset();
  }

  @Override public Entry<E> firstEntry() {
    return forwardMultiset().lastEntry();
  }

  @Override public Entry<E> lastEntry() {
    return forwardMultiset().firstEntry();
  }

  abstract Iterator<Entry entryIterator();

  private transient Set<Entry entrySet;

  @Override public Set<Entry entrySet() {
    Set<Entry result = entrySet;
    return (result == null) ? entrySet = createEntrySet() : result;
  }

  Set<Entry createEntrySet() {
    return new Multisets.EntrySet<E>() {
      @Override Multiset<E> multiset() {
        return DescendingMultiset.this;
      }

      @Override public Iterator<Entry iterator() {
        return entryIterator();
      }

      @Override public int size() {
        return forwardMultiset().entrySet().size();
      }
    };
  }

  @Override public Iterator<E> iterator() {
    return Multisets.iteratorImpl(this);
  }

  @Override public Object[] toArray() {
    return standardToArray();
  }

  @Override public <T> T[] toArray(T[] array) {
    return standardToArray(array);
  }

  @Override public String toString() {
    return entrySet().toString();
  }
}

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