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/*
* Copyright (C) 2016 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.graph;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.annotations.Beta;
import com.google.common.base.MoreObjects;
import com.google.common.base.MoreObjects.ToStringHelper;
import com.google.common.base.Objects;
import com.google.common.collect.Maps;
import com.google.common.collect.Ordering;
import com.google.errorprone.annotations.Immutable;
import java.util.Comparator;
import java.util.Map;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Used to represent the order of elements in a data structure that supports different options for
* iteration order guarantees.
*
* <p>Example usage:
*
* <pre>{@code
* MutableGraph<Integer> graph =
* GraphBuilder.directed().nodeOrder(ElementOrder.<Integer>natural()).build();
* }</pre>
*
* @author Joshua O'Madadhain
* @since 20.0
*/
@Beta
@Immutable
public final class ElementOrder<T> {
private final Type type;
@SuppressWarnings("Immutable") // Hopefully the comparator provided is immutable!
private final @Nullable Comparator<T> comparator;
/**
* The type of ordering that this object specifies.
*
* <ul>
* <li>UNORDERED: no order is guaranteed.
* <li>STABLE: ordering is guaranteed to follow a pattern that won't change between releases.
* Some methods may have stronger guarantees.
* <li>INSERTION: insertion ordering is guaranteed.
* <li>SORTED: ordering according to a supplied comparator is guaranteed.
* </ul>
*/
public enum Type {
UNORDERED,
STABLE,
INSERTION,
SORTED
}
private ElementOrder(Type type, @Nullable Comparator<T> comparator) {
this.type = checkNotNull(type);
this.comparator = comparator;
checkState((type == Type.SORTED) == (comparator != null));
}
/** Returns an instance which specifies that no ordering is guaranteed. */
public static <S> ElementOrder<S> unordered() {
return new ElementOrder<S>(Type.UNORDERED, null);
}
/**
* Returns an instance which specifies that ordering is guaranteed to be always be the same across
* iterations, and across releases. Some methods may have stronger guarantees.
*
* <p>This instance is only useful in combination with {@code incidentEdgeOrder}, e.g. {@code
* graphBuilder.incidentEdgeOrder(ElementOrder.stable())}.
*
* <h3>In combination with {@code incidentEdgeOrder}</h3>
*
* <p>{@code incidentEdgeOrder(ElementOrder.stable())} guarantees the ordering of the returned
* collections of the following methods:
*
* <ul>
* <li>For {@link Graph} and {@link ValueGraph}:
* <ul>
* <li>{@code edges()}: Stable order
* <li>{@code adjacentNodes(node)}: Connecting edge insertion order
* <li>{@code predecessors(node)}: Connecting edge insertion order
* <li>{@code successors(node)}: Connecting edge insertion order
* <li>{@code incidentEdges(node)}: Edge insertion order
* </ul>
* <li>For {@link Network}:
* <ul>
* <li>{@code adjacentNodes(node)}: Stable order
* <li>{@code predecessors(node)}: Connecting edge insertion order
* <li>{@code successors(node)}: Connecting edge insertion order
* <li>{@code incidentEdges(node)}: Stable order
* <li>{@code inEdges(node)}: Edge insertion order
* <li>{@code outEdges(node)}: Edge insertion order
* <li>{@code adjacentEdges(edge)}: Stable order
* <li>{@code edgesConnecting(nodeU, nodeV)}: Edge insertion order
* </ul>
* </ul>
*
* @since 29.0
*/
public static <S> ElementOrder<S> stable() {
return new ElementOrder<S>(Type.STABLE, null);
}
/** Returns an instance which specifies that insertion ordering is guaranteed. */
public static <S> ElementOrder<S> insertion() {
return new ElementOrder<S>(Type.INSERTION, null);
}
/**
* Returns an instance which specifies that the natural ordering of the elements is guaranteed.
*/
public static <S extends Comparable<? super S>> ElementOrder<S> natural() {
return new ElementOrder<S>(Type.SORTED, Ordering.<S>natural());
}
/**
* Returns an instance which specifies that the ordering of the elements is guaranteed to be
* determined by {@code comparator}.
*/
public static <S> ElementOrder<S> sorted(Comparator<S> comparator) {
return new ElementOrder<S>(Type.SORTED, checkNotNull(comparator));
}
/** Returns the type of ordering used. */
public Type type() {
return type;
}
/**
* Returns the {@link Comparator} used.
*
* @throws UnsupportedOperationException if comparator is not defined
*/
public Comparator<T> comparator() {
if (comparator != null) {
return comparator;
}
throw new UnsupportedOperationException("This ordering does not define a comparator.");
}
@Override
public boolean equals(@Nullable Object obj) {
if (obj == this) {
return true;
}
if (!(obj instanceof ElementOrder)) {
return false;
}
ElementOrder<?> other = (ElementOrder<?>) obj;
return (type == other.type) && Objects.equal(comparator, other.comparator);
}
@Override
public int hashCode() {
return Objects.hashCode(type, comparator);
}
@Override
public String toString() {
ToStringHelper helper = MoreObjects.toStringHelper(this).add("type", type);
if (comparator != null) {
helper.add("comparator", comparator);
}
return helper.toString();
}
/** Returns an empty mutable map whose keys will respect this {@link ElementOrder}. */
<K extends T, V> Map<K, V> createMap(int expectedSize) {
switch (type) {
case UNORDERED:
return Maps.newHashMapWithExpectedSize(expectedSize);
case INSERTION:
case STABLE:
return Maps.newLinkedHashMapWithExpectedSize(expectedSize);
case SORTED:
return Maps.newTreeMap(comparator());
default:
throw new AssertionError();
}
}
@SuppressWarnings("unchecked")
<T1 extends T> ElementOrder<T1> cast() {
return (ElementOrder<T1>) this;
}
}
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