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Java example source code file (ElementOrder.java)
This example Java source code file (ElementOrder.java) is included in the alvinalexander.com
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Learn more about this Java project at its project page.
The ElementOrder.java Java example source code
/*
* 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 com.google.common.base.MoreObjects;
import com.google.common.base.MoreObjects.ToStringHelper;
import com.google.common.base.Objects;
import com.google.common.base.Preconditions;
import com.google.common.collect.Ordering;
import java.util.Comparator;
import javax.annotation.Nullable;
/**
* Used to represent the order of elements in a data structure that supports different options
* for iteration order guarantees.
*
* <p>Example usage:
* <pre>
* MutableGraph<Integer> graph
* = GraphBuilder.directed().nodeOrder(ElementOrder.natural()).build();
* </code>
*/
public class ElementOrder<T> {
private final Type type;
@Nullable private final Comparator<T> comparator;
/**
* The type of ordering that this object specifies.
* <ul>
* <li>UNORDERED: no order is guaranteed.
* <li>INSERTION: insertion ordering is guaranteed.
* <li>SORTED: ordering according to a supplied comparator is guaranteed.
* </ul>
*/
public enum Type {
UNORDERED,
INSERTION,
SORTED
}
private ElementOrder(Type type, @Nullable Comparator<T> comparator) {
this.type = Preconditions.checkNotNull(type);
Preconditions.checkArgument((type == Type.SORTED) == (comparator != null),
"if the type is SORTED, the comparator should be non-null; otherwise, it should be null");
this.comparator = comparator;
}
/**
* Returns the type of ordering used.
*/
public Type type() {
return type;
}
/**
* Returns the {@link Comparator} used.
*
* @throws IllegalStateException if no comparator is defined
*/
public Comparator<T> comparator() {
if (comparator != null) {
return comparator;
}
throw new IllegalStateException("This ordering does not define a comparator");
}
@Override
public boolean equals(Object o) {
if (!(o instanceof ElementOrder)) {
return false;
}
ElementOrder<?> other = (ElementOrder) o;
return other.type == this.type
&& Objects.equal(other.comparator, this.comparator);
}
@Override
public int hashCode() {
return Objects.hashCode(this.type, this.comparator);
}
@Override
public String toString() {
ToStringHelper helper = MoreObjects.toStringHelper(this)
.add("type", this.type);
if (this.comparator != null) {
helper.add("comparator", this.comparator);
}
return helper.toString();
}
/**
* Returns an instance which specifies that no ordering is guaranteed.
*/
public static final <S> ElementOrder unordered() {
return new ElementOrder<S>(Type.UNORDERED, null);
}
/**
* Returns an instance which specifies that insertion ordering is guaranteed.
*/
public static final <S> ElementOrder insertion() {
return new ElementOrder<S>(Type.INSERTION, null);
}
/**
* Returns an instance which specifies that the natural ordering of the elements is guaranteed.
*/
public static final <S extends Comparable ElementOrder natural() {
return new ElementOrder<S>(Type.SORTED, Ordering.natural());
}
/**
* Returns an instance which specifies that the ordering of the elements is guaranteed to be
* determined by {@code comparator}.
*/
public static final <S extends Comparable ElementOrder sorted(Comparator comparator) {
return new ElementOrder<S>(Type.SORTED, comparator);
}
}
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