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
019/**
020 * <p>An immutable triple consisting of three {@code Object} elements.</p>
021 *
022 * <p>Although the implementation is immutable, there is no restriction on the objects
023 * that may be stored. If mutable objects are stored in the triple, then the triple
024 * itself effectively becomes mutable. The class is also {@code final}, so a subclass
025 * can not add undesirable behaviour.</p>
026 *
027 * <p>#ThreadSafe# if all three objects are thread-safe</p>
028 *
029 * @param <L> the left element type
030 * @param <M> the middle element type
031 * @param <R> the right element type
032 *
033 * @since 3.2
034 */
035public final class ImmutableTriple<L, M, R> extends Triple<L, M, R> {
036
037    /**
038     * An empty array.
039     * <p>
040     * Consider using {@link #emptyArray()} to avoid generics warnings.
041     * </p>
042     *
043     * @since 3.10.
044     */
045    public static final ImmutableTriple<?, ?, ?>[] EMPTY_ARRAY = new ImmutableTriple[0];
046
047    /**
048     * An immutable triple of nulls.
049     */
050    // This is not defined with generics to avoid warnings in call sites.
051    @SuppressWarnings("rawtypes")
052    private static final ImmutableTriple NULL = of(null, null, null);
053
054    /** Serialization version */
055    private static final long serialVersionUID = 1L;
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 <M> the middle 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, M, R> ImmutableTriple<L, M, R>[] emptyArray() {
069        return (ImmutableTriple<L, M, R>[]) EMPTY_ARRAY;
070    }
071
072    /**
073     * Returns an immutable triple of nulls.
074     *
075     * @param <L> the left element of this triple. Value is {@code null}.
076     * @param <M> the middle element of this triple. Value is {@code null}.
077     * @param <R> the right element of this triple. Value is {@code null}.
078     * @return an immutable triple of nulls.
079     * @since 3.6
080     */
081    public static <L, M, R> ImmutableTriple<L, M, R> nullTriple() {
082        return NULL;
083    }
084
085    /**
086     * <p>Obtains an immutable triple of three objects inferring the generic types.</p>
087     *
088     * <p>This factory allows the triple to be created using inference to
089     * obtain the generic types.</p>
090     *
091     * @param <L> the left element type
092     * @param <M> the middle element type
093     * @param <R> the right element type
094     * @param left  the left element, may be null
095     * @param middle  the middle element, may be null
096     * @param right  the right element, may be null
097     * @return a triple formed from the three parameters, not null
098     */
099    public static <L, M, R> ImmutableTriple<L, M, R> of(final L left, final M middle, final R right) {
100        return new ImmutableTriple<>(left, middle, right);
101    }
102    /** Left object */
103    public final L left;
104    /** Middle object */
105    public final M middle;
106
107    /** Right object */
108    public final R right;
109
110    /**
111     * Create a new triple instance.
112     *
113     * @param left  the left value, may be null
114     * @param middle the middle value, may be null
115     * @param right  the right value, may be null
116     */
117    public ImmutableTriple(final L left, final M middle, final R right) {
118        super();
119        this.left = left;
120        this.middle = middle;
121        this.right = right;
122    }
123
124    //-----------------------------------------------------------------------
125    /**
126     * {@inheritDoc}
127     */
128    @Override
129    public L getLeft() {
130        return left;
131    }
132
133    /**
134     * {@inheritDoc}
135     */
136    @Override
137    public M getMiddle() {
138        return middle;
139    }
140
141    /**
142     * {@inheritDoc}
143     */
144    @Override
145    public R getRight() {
146        return right;
147    }
148}
149