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.util.Map;
020
021/**
022 * <p>An immutable pair consisting of two {@code Object} elements.</p>
023 *
024 * <p>Although the implementation is immutable, there is no restriction on the objects
025 * that may be stored. If mutable objects are stored in the pair, then the pair
026 * itself effectively becomes mutable. The class is also {@code final}, so a subclass
027 * can not add undesirable behavior.</p>
028 *
029 * <p>#ThreadSafe# if both paired objects are thread-safe</p>
030 *
031 * @param <L> the left element type
032 * @param <R> the right element type
033 *
034 * @since 3.0
035 */
036public final class ImmutablePair<L, R> extends Pair<L, R> {
037
038    /**
039     * An empty array.
040     * <p>
041     * Consider using {@link #emptyArray()} to avoid generics warnings.
042     * </p>
043     *
044     * @since 3.10.
045     */
046    public static final ImmutablePair<?, ?>[] EMPTY_ARRAY = new ImmutablePair[0];
047
048    /**
049     * An immutable pair of nulls.
050     */
051    // This is not defined with generics to avoid warnings in call sites.
052    @SuppressWarnings("rawtypes")
053    private static final ImmutablePair NULL = of(null, null);
054
055    /** Serialization version */
056    private static final long serialVersionUID = 4954918890077093841L;
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> ImmutablePair<L, R>[] emptyArray() {
069        return (ImmutablePair<L, R>[]) EMPTY_ARRAY;
070    }
071
072    /**
073     * <p>Creates an immutable pair of two objects inferring the generic types.</p>
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     * @return a pair formed from the two parameters, not null
082     * @since 3.11
083     */
084    public static <L, R> Pair<L, R> left(final L left) {
085        return ImmutablePair.of(left, null);
086    }
087
088    /**
089     * Returns an immutable pair of nulls.
090     *
091     * @param <L> the left element of this pair. Value is {@code null}.
092     * @param <R> the right element of this pair. Value is {@code null}.
093     * @return an immutable pair of nulls.
094     * @since 3.6
095     */
096    public static <L, R> ImmutablePair<L, R> nullPair() {
097        return NULL;
098    }
099
100    /**
101     * <p>Creates an immutable pair of two objects inferring the generic types.</p>
102     *
103     * <p>This factory allows the pair to be created using inference to
104     * obtain the generic types.</p>
105     *
106     * @param <L> the left element type
107     * @param <R> the right element type
108     * @param left  the left element, may be null
109     * @param right  the right element, may be null
110     * @return a pair formed from the two parameters, not null
111     */
112    public static <L, R> ImmutablePair<L, R> of(final L left, final R right) {
113        return new ImmutablePair<>(left, right);
114    }
115
116    /**
117     * <p>Creates an immutable pair from an existing pair.</p>
118     *
119     * <p>This factory allows the pair to be created using inference to
120     * obtain the generic types.</p>
121     *
122     * @param <L> the left element type
123     * @param <R> the right element type
124     * @param pair the existing pair.
125     * @return a pair formed from the two parameters, not null
126     * @since 3.10
127     */
128    public static <L, R> ImmutablePair<L, R> of(final Map.Entry<L, R> pair) {
129        final L left;
130        final R right;
131        if (pair != null) {
132            left = pair.getKey();
133            right = pair.getValue();
134        } else {
135            left = null;
136            right = null;
137        }
138        return new ImmutablePair<>(left, right);
139    }
140
141    /**
142     * <p>Creates an immutable pair of two objects inferring the generic types.</p>
143     *
144     * <p>This factory allows the pair to be created using inference to
145     * obtain the generic types.</p>
146     *
147     * @param <L> the left element type
148     * @param <R> the right element type
149     * @param right  the right element, may be null
150     * @return a pair formed from the two parameters, not null
151     * @since 3.11
152     */
153    public static <L, R> Pair<L, R> right(final R right) {
154        return ImmutablePair.of(null, right);
155    }
156
157    /** Left object */
158    public final L left;
159
160    /** Right object */
161    public final R right;
162
163    /**
164     * Create a new pair instance.
165     *
166     * @param left  the left value, may be null
167     * @param right  the right value, may be null
168     */
169    public ImmutablePair(final L left, final R right) {
170        this.left = left;
171        this.right = right;
172    }
173
174    /**
175     * {@inheritDoc}
176     */
177    @Override
178    public L getLeft() {
179        return left;
180    }
181
182    /**
183     * {@inheritDoc}
184     */
185    @Override
186    public R getRight() {
187        return right;
188    }
189
190    /**
191     * <p>Throws {@code UnsupportedOperationException}.</p>
192     *
193     * <p>This pair is immutable, so this operation is not supported.</p>
194     *
195     * @param value  the value to set
196     * @return never
197     * @throws UnsupportedOperationException as this operation is not supported
198     */
199    @Override
200    public R setValue(final R value) {
201        throw new UnsupportedOperationException();
202    }
203
204}