Pair.java
/*
* 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
*
* https://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;
import org.apache.commons.lang3.function.FailableBiConsumer;
import org.apache.commons.lang3.function.FailableBiFunction;
/**
* A pair consisting of two elements.
*
* <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 3.0
*/
public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
/** Serialization version */
private static final long serialVersionUID = 4954918890077093841L;
/**
* An empty array.
* <p>
* Consider using {@link #emptyArray()} to avoid generics warnings.
* </p>
*
* @since 3.10
*/
public static final Pair<?, ?>[] EMPTY_ARRAY = {};
/**
* Returns the empty array singleton that can be assigned without compiler warning.
*
* @param <L> the left element type.
* @param <R> the right element type.
* @return the empty array singleton that can be assigned without compiler warning.
* @since 3.10
*/
@SuppressWarnings("unchecked")
public static <L, R> Pair<L, R>[] emptyArray() {
return (Pair<L, R>[]) EMPTY_ARRAY;
}
/**
* Creates an immutable pair of two objects inferring the generic types.
*
* <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 ImmutablePair.of(left, right);
}
/**
* Creates an immutable pair from a map entry.
*
* <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 pair the map entry.
* @return a pair formed from the map entry.
* @since 3.10
*/
public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
return ImmutablePair.of(pair);
}
/**
* Creates an immutable pair of two non-null objects inferring the generic types.
*
* <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 not be null.
* @param right the right element, may not be null.
* @return a pair formed from the two parameters, not null.
* @throws NullPointerException if any input is null.
* @since 3.13.0
*/
public static <L, R> Pair<L, R> ofNonNull(final L left, final R right) {
return ImmutablePair.ofNonNull(left, right);
}
/**
* Constructs a new instance.
*/
public Pair() {
// empty
}
/**
* Accepts this key and value as arguments to the given consumer.
*
* @param <E> The kind of thrown exception or error.
* @param consumer the consumer to call.
* @throws E Thrown when the consumer fails.
* @since 3.13.0
*/
public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
consumer.accept(getKey(), getValue());
}
/**
* Applies this key and value as arguments to the given function.
*
* @param <V> The function return type.
* @param <E> The kind of thrown exception or error.
* @param function the consumer to call.
* @return the function's return value.
* @throws E Thrown when the consumer fails.
* @since 3.13.0
*/
public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
return function.apply(getKey(), getValue());
}
/**
* Compares the pair based on the left element followed by the right element.
* The types must be {@link 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<L, R> other) {
// @formatter:off
return new CompareToBuilder()
.append(getLeft(), other.getLeft())
.append(getRight(), other.getRight())
.toComparison();
// @formatter:on
}
/**
* 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.
*
* <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();
}
/**
* Gets the left element from this pair.
*
* <p>When treated as a key-value pair, this is the key.</p>
*
* @return the left element, may be null.
*/
public abstract L getLeft();
/**
* Gets the right element from this pair.
*
* <p>When treated as a key-value pair, this is the value.</p>
*
* @return the right element, may be null.
*/
public abstract R getRight();
/**
* Gets the value from this pair.
*
* <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();
}
/**
* Returns a suitable hash code.
* <p>
* 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 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.
*
* <p>
* This uses {@link String#format(String, Object...)} to the format. 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).
* </p>
*
* @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null.
* @return the formatted string, not null.
* @see String#format(String, Object...)
*/
public String toString(final String format) {
return String.format(format, getLeft(), getRight());
}
}