Java tutorial
/* * 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.Beta; import java.util.Iterator; import java.util.NavigableSet; import java.util.SortedSet; /** * A navigable set which forwards all its method calls to another navigable set. Subclasses should * override one or more methods to modify the behavior of the backing set as desired per the <a * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. * * <p><i>Warning:</i> The methods of {@code ForwardingNavigableSet} forward <i>indiscriminately</i> * to the methods of the delegate. For example, overriding {@link #add} alone <i>will not</i> * change the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you * should override {@code addAll} as well, either providing your own implementation, or delegating * to the provided {@code standardAddAll} method. * * <p>Each of the {@code standard} methods uses the set's comparator (or the natural ordering of * the elements, if there is no comparator) to test element equality. As a result, if the * comparator is not consistent with equals, some of the standard implementations may violate the * {@code Set} contract. * * <p>The {@code standard} methods and the collection views they return are not guaranteed to be * thread-safe, even when all of the methods that they depend on are thread-safe. * * @author Louis Wasserman * @since 12.0 */ public abstract class ForwardingNavigableSet<E> extends ForwardingSortedSet<E> implements NavigableSet<E> { /** Constructor for use by subclasses. */ protected ForwardingNavigableSet() { } @Override protected abstract NavigableSet<E> delegate(); @Override public E lower(E e) { return delegate().lower(e); } /** * A sensible definition of {@link #lower} in terms of the {@code descendingIterator} method of * {@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may * wish to override {@link #lower} to forward to this implementation. */ protected E standardLower(E e) { return Iterators.getNext(headSet(e, false).descendingIterator(), null); } @Override public E floor(E e) { return delegate().floor(e); } /** * A sensible definition of {@link #floor} in terms of the {@code descendingIterator} method of * {@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may * wish to override {@link #floor} to forward to this implementation. */ protected E standardFloor(E e) { return Iterators.getNext(headSet(e, true).descendingIterator(), null); } @Override public E ceiling(E e) { return delegate().ceiling(e); } /** * A sensible definition of {@link #ceiling} in terms of the {@code iterator} method of * {@link #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may * wish to override {@link #ceiling} to forward to this implementation. */ protected E standardCeiling(E e) { return Iterators.getNext(tailSet(e, true).iterator(), null); } @Override public E higher(E e) { return delegate().higher(e); } /** * A sensible definition of {@link #higher} in terms of the {@code iterator} method of * {@link #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may * wish to override {@link #higher} to forward to this implementation. */ protected E standardHigher(E e) { return Iterators.getNext(tailSet(e, false).iterator(), null); } @Override public E pollFirst() { return delegate().pollFirst(); } /** * A sensible definition of {@link #pollFirst} in terms of the {@code iterator} method. If you * override {@link #iterator} you may wish to override {@link #pollFirst} to forward to this * implementation. */ protected E standardPollFirst() { return Iterators.pollNext(iterator()); } @Override public E pollLast() { return delegate().pollLast(); } /** * A sensible definition of {@link #pollLast} in terms of the {@code descendingIterator} method. * If you override {@link #descendingIterator} you may wish to override {@link #pollLast} to * forward to this implementation. */ protected E standardPollLast() { return Iterators.pollNext(descendingIterator()); } protected E standardFirst() { return iterator().next(); } protected E standardLast() { return descendingIterator().next(); } @Override public NavigableSet<E> descendingSet() { return delegate().descendingSet(); } /** * A sensible implementation of {@link NavigableSet#descendingSet} in terms of the other methods * of {@link NavigableSet}, notably including {@link NavigableSet#descendingIterator}. * * <p>In many cases, you may wish to override {@link ForwardingNavigableSet#descendingSet} to * forward to this implementation or a subclass thereof. * * @since 12.0 */ @Beta protected class StandardDescendingSet extends Sets.DescendingSet<E> { /** Constructor for use by subclasses. */ public StandardDescendingSet() { super(ForwardingNavigableSet.this); } } @Override public Iterator<E> descendingIterator() { return delegate().descendingIterator(); } @Override public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { return delegate().subSet(fromElement, fromInclusive, toElement, toInclusive); } /** * A sensible definition of {@link #subSet(Object, boolean, Object, boolean)} in terms of the * {@code headSet} and {@code tailSet} methods. In many cases, you may wish to override * {@link #subSet(Object, boolean, Object, boolean)} to forward to this implementation. */ @Beta protected NavigableSet<E> standardSubSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) { return tailSet(fromElement, fromInclusive).headSet(toElement, toInclusive); } /** * A sensible definition of {@link #subSet(Object, Object)} in terms of the * {@link #subSet(Object, boolean, Object, boolean)} method. If you override * {@link #subSet(Object, boolean, Object, boolean)}, you may wish to override * {@link #subSet(Object, Object)} to forward to this implementation. */ @Override protected SortedSet<E> standardSubSet(E fromElement, E toElement) { return subSet(fromElement, true, toElement, false); } @Override public NavigableSet<E> headSet(E toElement, boolean inclusive) { return delegate().headSet(toElement, inclusive); } /** * A sensible definition of {@link #headSet(Object)} in terms of the * {@link #headSet(Object, boolean)} method. If you override * {@link #headSet(Object, boolean)}, you may wish to override * {@link #headSet(Object)} to forward to this implementation. */ protected SortedSet<E> standardHeadSet(E toElement) { return headSet(toElement, false); } @Override public NavigableSet<E> tailSet(E fromElement, boolean inclusive) { return delegate().tailSet(fromElement, inclusive); } /** * A sensible definition of {@link #tailSet(Object)} in terms of the * {@link #tailSet(Object, boolean)} method. If you override * {@link #tailSet(Object, boolean)}, you may wish to override * {@link #tailSet(Object)} to forward to this implementation. */ protected SortedSet<E> standardTailSet(E fromElement) { return tailSet(fromElement, true); } }