    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.Objects;
    021
    022import org.apache.commons.lang3.builder.CompareToBuilder;
    023
    024/**
    025 * <p>A triple consisting of three elements.</p>
    026 *
    027 * <p>This class is an abstract implementation defining the basic API.
    028 * It refers to the elements as 'left', 'middle' and 'right'.</p>
    029 *
    030 * <p>Subclass implementations may be mutable or immutable.
    031 * However, there is no restriction on the type of the stored objects that may be stored.
    032 * If mutable objects are stored in the triple, then the triple itself effectively becomes mutable.</p>
    033 *
    034 * @param <L> the left element type
    035 * @param <M> the middle element type
    036 * @param <R> the right element type
    037 *
    038 * @since 3.2
    039 */
    040public abstract class Triple<L, M, R> implements Comparable<Triple<L, M, R>>, Serializable {
    041
    042    private static final class TripleAdapter<L, M, R> extends Triple<L, M, R> {
    043
    044        private static final long serialVersionUID = 1L;
    045
    046        @Override
    047        public L getLeft() {
    048            return null;
    049        }
    050
    051        @Override
    052        public M getMiddle() {
    053            return null;
    054        }
    055
    056        @Override
    057        public R getRight() {
    058            return null;
    059        }
    060
    061    }
    062
    063    /** Serialization version */
    064    private static final long serialVersionUID = 1L;
    065
    066    /**
    067     * An empty array.
    068     * <p>
    069     * Consider using {@link #emptyArray()} to avoid generics warnings.
    070     * </p>
    071     *
    072     * @since 3.10.
    073     */
    074    public static final Triple<?, ?, ?>[] EMPTY_ARRAY = new TripleAdapter[0];
    075
    076    /**
    077     * Returns the empty array singleton that can be assigned without compiler warning.
    078     *
    079     * @param <L> the left element type
    080     * @param <M> the middle element type
    081     * @param <R> the right element type
    082     * @return the empty array singleton that can be assigned without compiler warning.
    083     *
    084     * @since 3.10.
    085     */
    086    @SuppressWarnings("unchecked")
    087    public static <L, M, R> Triple<L, M, R>[] emptyArray() {
    088        return (Triple<L, M, R>[]) EMPTY_ARRAY;
    089    }
    090
    091    /**
    092     * <p>Obtains an immutable triple of three objects inferring the generic types.</p>
    093     *
    094     * <p>This factory allows the triple to be created using inference to
    095     * obtain the generic types.</p>
    096     *
    097     * @param <L> the left element type
    098     * @param <M> the middle element type
    099     * @param <R> the right element type
    100     * @param left  the left element, may be null
    101     * @param middle the middle element, may be null
    102     * @param right  the right element, may be null
    103     * @return a triple formed from the three parameters, not null
    104     */
    105    public static <L, M, R> Triple<L, M, R> of(final L left, final M middle, final R right) {
    106        return new ImmutableTriple<>(left, middle, right);
    107    }
    108
    109    //-----------------------------------------------------------------------
    110    /**
    111     * <p>Compares the triple based on the left element, followed by the middle element,
    112     * finally the right element.
    113     * The types must be {@code Comparable}.</p>
    114     *
    115     * @param other  the other triple, not null
    116     * @return negative if this is less, zero if equal, positive if greater
    117     */
    118    @Override
    119    public int compareTo(final Triple<L, M, R> other) {
    120      return new CompareToBuilder().append(getLeft(), other.getLeft())
    121          .append(getMiddle(), other.getMiddle())
    122          .append(getRight(), other.getRight()).toComparison();
    123    }
    124
    125    /**
    126     * <p>Compares this triple to another based on the three elements.</p>
    127     *
    128     * @param obj  the object to compare to, null returns false
    129     * @return true if the elements of the triple are equal
    130     */
    131    @Override
    132    public boolean equals(final Object obj) {
    133        if (obj == this) {
    134            return true;
    135        }
    136        if (obj instanceof Triple<?, ?, ?>) {
    137            final Triple<?, ?, ?> other = (Triple<?, ?, ?>) obj;
    138            return Objects.equals(getLeft(), other.getLeft())
    139                && Objects.equals(getMiddle(), other.getMiddle())
    140                && Objects.equals(getRight(), other.getRight());
    141        }
    142        return false;
    143    }
    144
    145    //-----------------------------------------------------------------------
    146    /**
    147     * <p>Gets the left element from this triple.</p>
    148     *
    149     * @return the left element, may be null
    150     */
    151    public abstract L getLeft();
    152
    153    /**
    154     * <p>Gets the middle element from this triple.</p>
    155     *
    156     * @return the middle element, may be null
    157     */
    158    public abstract M getMiddle();
    159
    160    /**
    161     * <p>Gets the right element from this triple.</p>
    162     *
    163     * @return the right element, may be null
    164     */
    165    public abstract R getRight();
    166
    167    /**
    168     * <p>Returns a suitable hash code.</p>
    169     *
    170     * @return the hash code
    171     */
    172    @Override
    173    public int hashCode() {
    174        return (getLeft() == null ? 0 : getLeft().hashCode()) ^
    175            (getMiddle() == null ? 0 : getMiddle().hashCode()) ^
    176            (getRight() == null ? 0 : getRight().hashCode());
    177    }
    178
    179    /**
    180     * <p>Returns a String representation of this triple using the format {@code ($left,$middle,$right)}.</p>
    181     *
    182     * @return a string describing this object, not null
    183     */
    184    @Override
    185    public String toString() {
    186        return "(" + getLeft() + "," + getMiddle() + "," + getRight() + ")";
    187    }
    188
    189    /**
    190     * <p>Formats the receiver using the given format.</p>
    191     *
    192     * <p>This uses {@link java.util.Formattable} to perform the formatting. Three variables may
    193     * be used to embed the left and right elements. Use {@code %1$s} for the left
    194     * element, {@code %2$s} for the middle and {@code %3$s} for the right element.
    195     * The default format used by {@code toString()} is {@code (%1$s,%2$s,%3$s)}.</p>
    196     *
    197     * @param format  the format string, optionally containing {@code %1$s}, {@code %2$s} and {@code %3$s}, not null
    198     * @return the formatted string, not null
    199     */
    200    public String toString(final String format) {
    201        return String.format(format, getLeft(), getMiddle(), getRight());
    202    }
    203
    204}
    205