org.apache.commons.lang3.tuple.Pair Maven / Gradle / Ivy
/*
* 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 java.util.Objects;
import org.apache.commons.lang3.builder.CompareToBuilder;
/**
* A pair consisting of two elements.
*
* 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'.
*
* 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.
*
* @param the left element type
* @param the right element type
*
* @since 3.0
*/
public abstract class Pair implements Map.Entry, Comparable>, Serializable {
private static final class PairAdapter extends Pair {
private static final long serialVersionUID = 1L;
@Override
public L getLeft() {
return null;
}
@Override
public R getRight() {
return null;
}
@Override
public R setValue(final R value) {
return null;
}
}
/** Serialization version */
private static final long serialVersionUID = 4954918890077093841L;
/**
* An empty array.
*
* Consider using {@link #emptyArray()} to avoid generics warnings.
*
*
* @since 3.10.
*/
public static final Pair[] EMPTY_ARRAY = new PairAdapter[0];
/**
* Returns the empty array singleton that can be assigned without compiler warning.
*
* @param the left element type
* @param the right element type
* @return the empty array singleton that can be assigned without compiler warning.
*
* @since 3.10.
*/
@SuppressWarnings("unchecked")
public static Pair[] emptyArray() {
return (Pair[]) EMPTY_ARRAY;
}
/**
* Creates an immutable pair of two objects inferring the generic types.
*
* This factory allows the pair to be created using inference to
* obtain the generic types.
*
* @param the left element type
* @param 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 Pair of(final L left, final R right) {
return ImmutablePair.of(left, right);
}
/**
* Creates an immutable pair from an existing pair.
*
* This factory allows the pair to be created using inference to
* obtain the generic types.
*
* @param the left element type
* @param the right element type
* @param pair the existing pair.
* @return a pair formed from the two parameters, not null
* @since 3.10
*/
public static Pair of(final Map.Entry pair) {
return ImmutablePair.of(pair);
}
//-----------------------------------------------------------------------
/**
* Compares the pair based on the left element followed by the right element.
* The types must be {@code Comparable}.
*
* @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 other) {
return new CompareToBuilder().append(getLeft(), other.getLeft())
.append(getRight(), other.getRight()).toComparison();
}
/**
* Compares this pair to another based on the two elements.
*
* @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 Objects.equals(getKey(), other.getKey())
&& Objects.equals(getValue(), other.getValue());
}
return false;
}
/**
* Gets the key from this pair.
*
* This method implements the {@code Map.Entry} interface returning the
* left element as the key.
*
* @return the left element as the key, may be null
*/
@Override
public final L getKey() {
return getLeft();
}
//-----------------------------------------------------------------------
/**
* Gets the left element from this pair.
*
* When treated as a key-value pair, this is the key.
*
* @return the left element, may be null
*/
public abstract L getLeft();
/**
* Gets the right element from this pair.
*
* When treated as a key-value pair, this is the value.
*
* @return the right element, may be null
*/
public abstract R getRight();
/**
* Gets the value from this pair.
*
* This method implements the {@code Map.Entry} interface returning the
* right element as the value.
*
* @return the right element as the value, may be null
*/
@Override
public R getValue() {
return getRight();
}
/**
* Returns a suitable hash code.
* The hash code follows the definition in {@code Map.Entry}.
*
* @return the hash code
*/
@Override
public int hashCode() {
// see Map.Entry API specification
return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
}
/**
* Returns a String representation of this pair using the format {@code ($left,$right)}.
*
* @return a string describing this object, not null
*/
@Override
public String toString() {
return "(" + getLeft() + ',' + getRight() + ')';
}
/**
* Formats the receiver using the given format.
*
* 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)}.
*
* @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());
}
}