/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.commons.lang3.tuple;
import java.io.Serializable;
import java.util.Map;
import org.apache.commons.lang3.ObjectUtils;
import org.apache.commons.lang3.builder.CompareToBuilder;
/**
* <p>A pair consisting of two elements.</p>
*
* <p>This class is an abstract implementation defining the basic API.
* It refers to the elements as 'left' and 'right'. It also implements the
* {@code Map.Entry} interface where the key is 'left' and the value is 'right'.</p>
*
* <p>Subclass implementations may be mutable or immutable.
* However, there is no restriction on the type of the stored objects that may be stored.
* If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.</p>
*
* @param <L> the left element type
* @param <R> the right element type
*
* @since Lang 3.0
* @version $Id: Pair.java 1436770 2013-01-22 07:09:45Z ggregory $
*/
public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
/** Serialization version */
private static final long serialVersionUID = 4954918890077093841L;
/**
* <p>Obtains an immutable pair of from two objects inferring the generic types.</p>
*
* <p>This factory allows the pair to be created using inference to
* obtain the generic types.</p>
*
* @param <L> the left element type
* @param <R> the right element type
* @param left the left element, may be null
* @param right the right element, may be null
* @return a pair formed from the two parameters, not null
*/
public static <L, R> Pair<L, R> of(final L left, final R right) {
return new ImmutablePair<L, R>(left, right);
}
//-----------------------------------------------------------------------
/**
* <p>Gets the left element from this pair.</p>
*
* <p>When treated as a key-value pair, this is the key.</p>
*
* @return the left element, may be null
*/
public abstract L getLeft();
/**
* <p>Gets the right element from this pair.</p>
*
* <p>When treated as a key-value pair, this is the value.</p>
*
* @return the right element, may be null
*/
public abstract R getRight();
/**
* <p>Gets the key from this pair.</p>
*
* <p>This method implements the {@code Map.Entry} interface returning the
* left element as the key.</p>
*
* @return the left element as the key, may be null
*/
@Override
public final L getKey() {
return getLeft();
}
/**
* <p>Gets the value from this pair.</p>
*
* <p>This method implements the {@code Map.Entry} interface returning the
* right element as the value.</p>
*
* @return the right element as the value, may be null
*/
@Override
public R getValue() {
return getRight();
}
//-----------------------------------------------------------------------
/**
* <p>Compares the pair based on the left element followed by the right element.
* The types must be {@code Comparable}.</p>
*
* @param other the other pair, not null
* @return negative if this is less, zero if equal, positive if greater
*/
@Override
public int compareTo(final Pair<L, R> other) {
return new CompareToBuilder().append(getLeft(), other.getLeft())
.append(getRight(), other.getRight()).toComparison();
}
/**
* <p>Compares this pair to another based on the two elements.</p>
*
* @param obj the object to compare to, null returns false
* @return true if the elements of the pair are equal
*/
@Override
public boolean equals(final Object obj) {
if (obj == this) {
return true;
}
if (obj instanceof Map.Entry<?, ?>) {
final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
return ObjectUtils.equals(getKey(), other.getKey())
&& ObjectUtils.equals(getValue(), other.getValue());
}
return false;
}
/**
* <p>Returns a suitable hash code.
* The hash code follows the definition in {@code Map.Entry}.</p>
*
* @return the hash code
*/
@Override
public int hashCode() {
// see Map.Entry API specification
return (getKey() == null ? 0 : getKey().hashCode()) ^
(getValue() == null ? 0 : getValue().hashCode());
}
/**
* <p>Returns a String representation of this pair using the format {@code ($left,$right)}.</p>
*
* @return a string describing this object, not null
*/
@Override
public String toString() {
return new StringBuilder().append('(').append(getLeft()).append(',').append(getRight()).append(')').toString();
}
/**
* <p>Formats the receiver using the given format.</p>
*
* <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
* be used to embed the left and right elements. Use {@code %1$s} for the left
* element (key) and {@code %2$s} for the right element (value).
* The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
*
* @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
* @return the formatted string, not null
*/
public String toString(final String format) {
return String.format(format, getLeft(), getRight());
}
}