    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.lang3.tuple;
    018
    019import java.io.Serializable;
    020import java.util.Map;
    021import java.util.Objects;
    022
    023import org.apache.commons.lang3.builder.CompareToBuilder;
    024import org.apache.commons.lang3.function.FailableBiConsumer;
    025import org.apache.commons.lang3.function.FailableBiFunction;
    026
    027/**
    028 * A pair consisting of two elements.
    029 *
    030 * <p>This class is an abstract implementation defining the basic API.
    031 * It refers to the elements as 'left' and 'right'. It also implements the
    032 * {@code Map.Entry} interface where the key is 'left' and the value is 'right'.</p>
    033 *
    034 * <p>Subclass implementations may be mutable or immutable.
    035 * However, there is no restriction on the type of the stored objects that may be stored.
    036 * If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.</p>
    037 *
    038 * @param <L> the left element type.
    039 * @param <R> the right element type.
    040 * @since 3.0
    041 */
    042public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
    043
    044    /** Serialization version */
    045    private static final long serialVersionUID = 4954918890077093841L;
    046
    047    /**
    048     * An empty array.
    049     * <p>
    050     * Consider using {@link #emptyArray()} to avoid generics warnings.
    051     * </p>
    052     *
    053     * @since 3.10
    054     */
    055    public static final Pair<?, ?>[] EMPTY_ARRAY = {};
    056
    057    /**
    058     * Returns the empty array singleton that can be assigned without compiler warning.
    059     *
    060     * @param <L> the left element type.
    061     * @param <R> the right element type.
    062     * @return the empty array singleton that can be assigned without compiler warning.
    063     * @since 3.10
    064     */
    065    @SuppressWarnings("unchecked")
    066    public static <L, R> Pair<L, R>[] emptyArray() {
    067        return (Pair<L, R>[]) EMPTY_ARRAY;
    068    }
    069
    070    /**
    071     * Creates an immutable pair of two objects inferring the generic types.
    072     *
    073     * @param <L> the left element type.
    074     * @param <R> the right element type.
    075     * @param left  the left element, may be null.
    076     * @param right  the right element, may be null.
    077     * @return an immutable pair formed from the two parameters, not null.
    078     */
    079    public static <L, R> Pair<L, R> of(final L left, final R right) {
    080        return ImmutablePair.of(left, right);
    081    }
    082
    083    /**
    084     * Creates an immutable pair from a map entry.
    085     *
    086     * @param <L> the left element type.
    087     * @param <R> the right element type.
    088     * @param pair the map entry.
    089     * @return an immutable pair formed from the map entry.
    090     * @since 3.10
    091     */
    092    public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
    093        return ImmutablePair.of(pair);
    094    }
    095
    096    /**
    097     * Creates an immutable pair of two non-null objects inferring the generic types.
    098     *
    099     * @param <L> the left element type.
    100     * @param <R> the right element type.
    101     * @param left  the left element, may not be null.
    102     * @param right  the right element, may not  be null.
    103     * @return an immutable pair formed from the two parameters, not null.
    104     * @throws NullPointerException if any input is null.
    105     * @since 3.13.0
    106     */
    107    public static <L, R> Pair<L, R> ofNonNull(final L left, final R right) {
    108        return ImmutablePair.ofNonNull(left, right);
    109    }
    110
    111    /**
    112     * Constructs a new instance.
    113     */
    114    public Pair() {
    115        // empty
    116    }
    117
    118    /**
    119     * Accepts this key and value as arguments to the given consumer.
    120     *
    121     * @param <E> The kind of thrown exception or error.
    122     * @param consumer the consumer to call.
    123     * @throws E Thrown when the consumer fails.
    124     * @since 3.13.0
    125     */
    126    public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
    127        consumer.accept(getKey(), getValue());
    128    }
    129
    130    /**
    131     * Applies this key and value as arguments to the given function.
    132     *
    133     * @param <V> The function return type.
    134     * @param <E> The kind of thrown exception or error.
    135     * @param function the consumer to call.
    136     * @return the function's return value.
    137     * @throws E Thrown when the consumer fails.
    138     * @since 3.13.0
    139     */
    140    public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
    141        return function.apply(getKey(), getValue());
    142    }
    143
    144    /**
    145     * Compares the pair based on the left element followed by the right element.
    146     * The types must be {@link Comparable}.
    147     *
    148     * @param other  the other pair, not null.
    149     * @return negative if this is less, zero if equal, positive if greater.
    150     */
    151    @Override
    152    public int compareTo(final Pair<L, R> other) {
    153        // @formatter:off
    154        return new CompareToBuilder()
    155            .append(getLeft(), other.getLeft())
    156            .append(getRight(), other.getRight())
    157            .toComparison();
    158        // @formatter:on
    159    }
    160
    161    /**
    162     * Compares this pair to another based on the two elements.
    163     *
    164     * @param obj  the object to compare to, null returns false.
    165     * @return true if the elements of the pair are equal.
    166     */
    167    @Override
    168    public boolean equals(final Object obj) {
    169        if (obj == this) {
    170            return true;
    171        }
    172        if (obj instanceof Map.Entry<?, ?>) {
    173            final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
    174            return Objects.equals(getKey(), other.getKey())
    175                    && Objects.equals(getValue(), other.getValue());
    176        }
    177        return false;
    178    }
    179
    180    /**
    181     * Gets the key from this pair.
    182     *
    183     * <p>This method implements the {@code Map.Entry} interface returning the
    184     * left element as the key.</p>
    185     *
    186     * @return the left element as the key, may be null.
    187     */
    188    @Override
    189    public final L getKey() {
    190        return getLeft();
    191    }
    192
    193    /**
    194     * Gets the left element from this pair.
    195     *
    196     * <p>When treated as a key-value pair, this is the key.</p>
    197     *
    198     * @return the left element, may be null.
    199     */
    200    public abstract L getLeft();
    201
    202    /**
    203     * Gets the right element from this pair.
    204     *
    205     * <p>When treated as a key-value pair, this is the value.</p>
    206     *
    207     * @return the right element, may be null.
    208     */
    209    public abstract R getRight();
    210
    211    /**
    212     * Gets the value from this pair.
    213     *
    214     * <p>This method implements the {@code Map.Entry} interface returning the
    215     * right element as the value.</p>
    216     *
    217     * @return the right element as the value, may be null.
    218     */
    219    @Override
    220    public R getValue() {
    221        return getRight();
    222    }
    223
    224    /**
    225     * Returns a suitable hash code.
    226     * <p>
    227     * The hash code follows the definition in {@code Map.Entry}.
    228     * </p>
    229     *
    230     * @return the hash code.
    231     */
    232    @Override
    233    public int hashCode() {
    234        // See Map.Entry API specification
    235        return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
    236    }
    237
    238    /**
    239     * Returns a String representation of this pair using the format {@code (left,right)}.
    240     *
    241     * @return a string describing this object, not null.
    242     */
    243    @Override
    244    public String toString() {
    245        return "(" + getLeft() + ',' + getRight() + ')';
    246    }
    247
    248    /**
    249     * Formats the receiver using the given format.
    250     *
    251     * <p>
    252     * 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$s} for
    253     * the left element (key) and {@code %2$s} for the right element (value).
    254     * </p>
    255     *
    256     * @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null.
    257     * @return the formatted string, not null.
    258     * @see String#format(String, Object...)
    259     */
    260    public String toString(final String format) {
    261        return String.format(format, getLeft(), getRight());
    262    }
    263
    264}