    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 *      http://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 *
    041 * @since 3.0
    042 */
    043public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
    044
    045    /** Serialization version */
    046    private static final long serialVersionUID = 4954918890077093841L;
    047
    048    /**
    049     * An empty array.
    050     * <p>
    051     * Consider using {@link #emptyArray()} to avoid generics warnings.
    052     * </p>
    053     *
    054     * @since 3.10.
    055     */
    056    public static final Pair<?, ?>[] EMPTY_ARRAY = {};
    057
    058    /**
    059     * Returns the empty array singleton that can be assigned without compiler warning.
    060     *
    061     * @param <L> the left element type
    062     * @param <R> the right element type
    063     * @return the empty array singleton that can be assigned without compiler warning.
    064     *
    065     * @since 3.10.
    066     */
    067    @SuppressWarnings("unchecked")
    068    public static <L, R> Pair<L, R>[] emptyArray() {
    069        return (Pair<L, R>[]) EMPTY_ARRAY;
    070    }
    071
    072    /**
    073     * Creates an immutable pair of two objects inferring the generic types.
    074     *
    075     * <p>This factory allows the pair to be created using inference to
    076     * obtain the generic types.</p>
    077     *
    078     * @param <L> the left element type
    079     * @param <R> the right element type
    080     * @param left  the left element, may be null
    081     * @param right  the right element, may be null
    082     * @return a pair formed from the two parameters, not null
    083     */
    084    public static <L, R> Pair<L, R> of(final L left, final R right) {
    085        return ImmutablePair.of(left, right);
    086    }
    087
    088    /**
    089     * Creates an immutable pair from a map entry.
    090     *
    091     * <p>This factory allows the pair to be created using inference to
    092     * obtain the generic types.</p>
    093     *
    094     * @param <L> the left element type
    095     * @param <R> the right element type
    096     * @param pair the map entry.
    097     * @return a pair formed from the map entry
    098     * @since 3.10
    099     */
    100    public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
    101        return ImmutablePair.of(pair);
    102    }
    103
    104    /**
    105     * Creates an immutable pair of two non-null objects inferring the generic types.
    106     *
    107     * <p>This factory allows the pair to be created using inference to
    108     * obtain the generic types.</p>
    109     *
    110     * @param <L> the left element type
    111     * @param <R> the right element type
    112     * @param left  the left element, may not be null
    113     * @param right  the right element, may not  be null
    114     * @return a pair formed from the two parameters, not null
    115     * @throws NullPointerException if any input is null
    116     * @since 3.13.0
    117     */
    118    public static <L, R> Pair<L, R> ofNonNull(final L left, final R right) {
    119        return ImmutablePair.ofNonNull(left, right);
    120    }
    121
    122    /**
    123     * Accepts this key and value as arguments to the given consumer.
    124     *
    125     * @param <E> The kind of thrown exception or error.
    126     * @param consumer the consumer to call.
    127     * @throws E Thrown when the consumer fails.
    128     * @since 3.13.0
    129     */
    130    public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
    131        consumer.accept(getKey(), getValue());
    132    }
    133
    134    /**
    135     * Applies this key and value as arguments to the given function.
    136     *
    137     * @param <V> The function return type.
    138     * @param <E> The kind of thrown exception or error.
    139     * @param function the consumer to call.
    140     * @return the function's return value.
    141     * @throws E Thrown when the consumer fails.
    142     * @since 3.13.0
    143     */
    144    public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
    145        return function.apply(getKey(), getValue());
    146    }
    147
    148    /**
    149     * Compares the pair based on the left element followed by the right element.
    150     * The types must be {@link Comparable}.
    151     *
    152     * @param other  the other pair, not null
    153     * @return negative if this is less, zero if equal, positive if greater
    154     */
    155    @Override
    156    public int compareTo(final Pair<L, R> other) {
    157      return new CompareToBuilder().append(getLeft(), other.getLeft())
    158              .append(getRight(), other.getRight()).toComparison();
    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     * The hash code follows the definition in {@code Map.Entry}.
    227     *
    228     * @return the hash code
    229     */
    230    @Override
    231    public int hashCode() {
    232        // see Map.Entry API specification
    233        return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
    234    }
    235
    236    /**
    237     * Returns a String representation of this pair using the format {@code ($left,$right)}.
    238     *
    239     * @return a string describing this object, not null
    240     */
    241    @Override
    242    public String toString() {
    243        return "(" + getLeft() + ',' + getRight() + ')';
    244    }
    245
    246    /**
    247     * Formats the receiver using the given format.
    248     *
    249     * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
    250     * be used to embed the left and right elements. Use {@code %1$s} for the left
    251     * element (key) and {@code %2$s} for the right element (value).
    252     * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
    253     *
    254     * @param format  the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
    255     * @return the formatted string, not null
    256     */
    257    public String toString(final String format) {
    258        return String.format(format, getLeft(), getRight());
    259    }
    260
    261}