001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.collect; 018 019import com.google.common.annotations.Beta; 020import com.google.common.annotations.GwtCompatible; 021import java.util.Comparator; 022import java.util.Iterator; 023import java.util.NoSuchElementException; 024import java.util.SortedSet; 025import org.checkerframework.checker.nullness.qual.Nullable; 026 027/** 028 * A sorted set which forwards all its method calls to another sorted set. Subclasses should 029 * override one or more methods to modify the behavior of the backing sorted set as desired per the 030 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 031 * 032 * <p><b>Warning:</b> The methods of {@code ForwardingSortedSet} forward <i>indiscriminately</i> to 033 * the methods of the delegate. For example, overriding {@link #add} alone <i>will not</i> change 034 * the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should 035 * override {@code addAll} as well, either providing your own implementation, or delegating to the 036 * provided {@code standardAddAll} method. 037 * 038 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code 039 * default} methods. Instead, it inherits their default implementations. When those implementations 040 * invoke methods, they invoke methods on the {@code ForwardingSortedSet}. 041 * 042 * <p>Each of the {@code standard} methods, where appropriate, uses the set's comparator (or the 043 * natural ordering of the elements, if there is no comparator) to test element equality. As a 044 * result, if the comparator is not consistent with equals, some of the standard implementations may 045 * violate the {@code Set} contract. 046 * 047 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be 048 * thread-safe, even when all of the methods that they depend on are thread-safe. 049 * 050 * @author Mike Bostock 051 * @author Louis Wasserman 052 * @since 2.0 053 */ 054@GwtCompatible 055public abstract class ForwardingSortedSet<E> extends ForwardingSet<E> implements SortedSet<E> { 056 057 /** Constructor for use by subclasses. */ 058 protected ForwardingSortedSet() {} 059 060 @Override 061 protected abstract SortedSet<E> delegate(); 062 063 @Override 064 public Comparator<? super E> comparator() { 065 return delegate().comparator(); 066 } 067 068 @Override 069 public E first() { 070 return delegate().first(); 071 } 072 073 @Override 074 public SortedSet<E> headSet(E toElement) { 075 return delegate().headSet(toElement); 076 } 077 078 @Override 079 public E last() { 080 return delegate().last(); 081 } 082 083 @Override 084 public SortedSet<E> subSet(E fromElement, E toElement) { 085 return delegate().subSet(fromElement, toElement); 086 } 087 088 @Override 089 public SortedSet<E> tailSet(E fromElement) { 090 return delegate().tailSet(fromElement); 091 } 092 093 // unsafe, but worst case is a CCE is thrown, which callers will be expecting 094 @SuppressWarnings("unchecked") 095 private int unsafeCompare(@Nullable Object o1, @Nullable Object o2) { 096 Comparator<? super E> comparator = comparator(); 097 return (comparator == null) 098 ? ((Comparable<Object>) o1).compareTo(o2) 099 : ((Comparator<Object>) comparator).compare(o1, o2); 100 } 101 102 /** 103 * A sensible definition of {@link #contains} in terms of the {@code first()} method of {@link 104 * #tailSet}. If you override {@link #tailSet}, you may wish to override {@link #contains} to 105 * forward to this implementation. 106 * 107 * @since 7.0 108 */ 109 @Override 110 @Beta 111 protected boolean standardContains(@Nullable Object object) { 112 try { 113 // any ClassCastExceptions are caught 114 @SuppressWarnings("unchecked") 115 SortedSet<Object> self = (SortedSet<Object>) this; 116 Object ceiling = self.tailSet(object).first(); 117 return unsafeCompare(ceiling, object) == 0; 118 } catch (ClassCastException | NoSuchElementException | NullPointerException e) { 119 return false; 120 } 121 } 122 123 /** 124 * A sensible definition of {@link #remove} in terms of the {@code iterator()} method of {@link 125 * #tailSet}. If you override {@link #tailSet}, you may wish to override {@link #remove} to 126 * forward to this implementation. 127 * 128 * @since 7.0 129 */ 130 @Override 131 @Beta 132 protected boolean standardRemove(@Nullable Object object) { 133 try { 134 // any ClassCastExceptions are caught 135 @SuppressWarnings("unchecked") 136 SortedSet<Object> self = (SortedSet<Object>) this; 137 Iterator<Object> iterator = self.tailSet(object).iterator(); 138 if (iterator.hasNext()) { 139 Object ceiling = iterator.next(); 140 if (unsafeCompare(ceiling, object) == 0) { 141 iterator.remove(); 142 return true; 143 } 144 } 145 } catch (ClassCastException | NullPointerException e) { 146 return false; 147 } 148 return false; 149 } 150 151 /** 152 * A sensible default implementation of {@link #subSet(Object, Object)} in terms of {@link 153 * #headSet(Object)} and {@link #tailSet(Object)}. In some situations, you may wish to override 154 * {@link #subSet(Object, Object)} to forward to this implementation. 155 * 156 * @since 7.0 157 */ 158 @Beta 159 protected SortedSet<E> standardSubSet(E fromElement, E toElement) { 160 return tailSet(fromElement).headSet(toElement); 161 } 162}