001/*
002 * Copyright (C) 2016 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.graph;
018
019import static com.google.common.base.Preconditions.checkNotNull;
020import static com.google.common.base.Preconditions.checkState;
021
022import com.google.common.annotations.Beta;
023import com.google.common.base.MoreObjects;
024import com.google.common.base.MoreObjects.ToStringHelper;
025import com.google.common.base.Objects;
026import com.google.common.collect.Maps;
027import com.google.common.collect.Ordering;
028import com.google.errorprone.annotations.Immutable;
029import java.util.Comparator;
030import java.util.Map;
031import org.checkerframework.checker.nullness.qual.Nullable;
032
033/**
034 * Used to represent the order of elements in a data structure that supports different options for
035 * iteration order guarantees.
036 *
037 * <p>Example usage:
038 *
039 * <pre>{@code
040 * MutableGraph<Integer> graph =
041 *     GraphBuilder.directed().nodeOrder(ElementOrder.<Integer>natural()).build();
042 * }</pre>
043 *
044 * @author Joshua O'Madadhain
045 * @since 20.0
046 */
047@Beta
048@Immutable
049public final class ElementOrder<T> {
050  private final Type type;
051
052  @SuppressWarnings("Immutable") // Hopefully the comparator provided is immutable!
053  private final @Nullable Comparator<T> comparator;
054
055  /**
056   * The type of ordering that this object specifies.
057   *
058   * <ul>
059   *   <li>UNORDERED: no order is guaranteed.
060   *   <li>INSERTION: insertion ordering is guaranteed.
061   *   <li>SORTED: ordering according to a supplied comparator is guaranteed.
062   * </ul>
063   */
064  public enum Type {
065    UNORDERED,
066    INSERTION,
067    SORTED
068  }
069
070  private ElementOrder(Type type, @Nullable Comparator<T> comparator) {
071    this.type = checkNotNull(type);
072    this.comparator = comparator;
073    checkState((type == Type.SORTED) == (comparator != null));
074  }
075
076  /** Returns an instance which specifies that no ordering is guaranteed. */
077  public static <S> ElementOrder<S> unordered() {
078    return new ElementOrder<S>(Type.UNORDERED, null);
079  }
080
081  /** Returns an instance which specifies that insertion ordering is guaranteed. */
082  public static <S> ElementOrder<S> insertion() {
083    return new ElementOrder<S>(Type.INSERTION, null);
084  }
085
086  /**
087   * Returns an instance which specifies that the natural ordering of the elements is guaranteed.
088   */
089  public static <S extends Comparable<? super S>> ElementOrder<S> natural() {
090    return new ElementOrder<S>(Type.SORTED, Ordering.<S>natural());
091  }
092
093  /**
094   * Returns an instance which specifies that the ordering of the elements is guaranteed to be
095   * determined by {@code comparator}.
096   */
097  public static <S> ElementOrder<S> sorted(Comparator<S> comparator) {
098    return new ElementOrder<S>(Type.SORTED, comparator);
099  }
100
101  /** Returns the type of ordering used. */
102  public Type type() {
103    return type;
104  }
105
106  /**
107   * Returns the {@link Comparator} used.
108   *
109   * @throws UnsupportedOperationException if comparator is not defined
110   */
111  public Comparator<T> comparator() {
112    if (comparator != null) {
113      return comparator;
114    }
115    throw new UnsupportedOperationException("This ordering does not define a comparator.");
116  }
117
118  @Override
119  public boolean equals(@Nullable Object obj) {
120    if (obj == this) {
121      return true;
122    }
123    if (!(obj instanceof ElementOrder)) {
124      return false;
125    }
126
127    ElementOrder<?> other = (ElementOrder<?>) obj;
128    return (type == other.type) && Objects.equal(comparator, other.comparator);
129  }
130
131  @Override
132  public int hashCode() {
133    return Objects.hashCode(type, comparator);
134  }
135
136  @Override
137  public String toString() {
138    ToStringHelper helper = MoreObjects.toStringHelper(this).add("type", type);
139    if (comparator != null) {
140      helper.add("comparator", comparator);
141    }
142    return helper.toString();
143  }
144
145  /** Returns an empty mutable map whose keys will respect this {@link ElementOrder}. */
146  <K extends T, V> Map<K, V> createMap(int expectedSize) {
147    switch (type) {
148      case UNORDERED:
149        return Maps.newHashMapWithExpectedSize(expectedSize);
150      case INSERTION:
151        return Maps.newLinkedHashMapWithExpectedSize(expectedSize);
152      case SORTED:
153        return Maps.newTreeMap(comparator());
154      default:
155        throw new AssertionError();
156    }
157  }
158
159  @SuppressWarnings("unchecked")
160  <T1 extends T> ElementOrder<T1> cast() {
161    return (ElementOrder<T1>) this;
162  }
163}