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     * <p>This factory allows the pair to be created using inference to
074     * obtain the generic types.</p>
075     *
076     * @param <L> the left element type.
077     * @param <R> the right element type.
078     * @param left  the left element, may be null.
079     * @param right  the right element, may be null.
080     * @return a pair formed from the two parameters, not null.
081     */
082    public static <L, R> Pair<L, R> of(final L left, final R right) {
083        return ImmutablePair.of(left, right);
084    }
085
086    /**
087     * Creates an immutable pair from a map entry.
088     *
089     * <p>This factory allows the pair to be created using inference to
090     * obtain the generic types.</p>
091     *
092     * @param <L> the left element type.
093     * @param <R> the right element type.
094     * @param pair the map entry.
095     * @return a pair formed from the map entry.
096     * @since 3.10
097     */
098    public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
099        return ImmutablePair.of(pair);
100    }
101
102    /**
103     * Creates an immutable pair of two non-null objects inferring the generic types.
104     *
105     * <p>This factory allows the pair to be created using inference to
106     * obtain the generic types.</p>
107     *
108     * @param <L> the left element type.
109     * @param <R> the right element type.
110     * @param left  the left element, may not be null.
111     * @param right  the right element, may not  be null.
112     * @return a pair formed from the two parameters, not null.
113     * @throws NullPointerException if any input is null.
114     * @since 3.13.0
115     */
116    public static <L, R> Pair<L, R> ofNonNull(final L left, final R right) {
117        return ImmutablePair.ofNonNull(left, right);
118    }
119
120    /**
121     * Constructs a new instance.
122     */
123    public Pair() {
124        // empty
125    }
126
127    /**
128     * Accepts this key and value as arguments to the given consumer.
129     *
130     * @param <E> The kind of thrown exception or error.
131     * @param consumer the consumer to call.
132     * @throws E Thrown when the consumer fails.
133     * @since 3.13.0
134     */
135    public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
136        consumer.accept(getKey(), getValue());
137    }
138
139    /**
140     * Applies this key and value as arguments to the given function.
141     *
142     * @param <V> The function return type.
143     * @param <E> The kind of thrown exception or error.
144     * @param function the consumer to call.
145     * @return the function's return value.
146     * @throws E Thrown when the consumer fails.
147     * @since 3.13.0
148     */
149    public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
150        return function.apply(getKey(), getValue());
151    }
152
153    /**
154     * Compares the pair based on the left element followed by the right element.
155     * The types must be {@link Comparable}.
156     *
157     * @param other  the other pair, not null.
158     * @return negative if this is less, zero if equal, positive if greater.
159     */
160    @Override
161    public int compareTo(final Pair<L, R> other) {
162        // @formatter:off
163        return new CompareToBuilder()
164            .append(getLeft(), other.getLeft())
165            .append(getRight(), other.getRight())
166            .toComparison();
167        // @formatter:on
168    }
169
170    /**
171     * Compares this pair to another based on the two elements.
172     *
173     * @param obj  the object to compare to, null returns false.
174     * @return true if the elements of the pair are equal.
175     */
176    @Override
177    public boolean equals(final Object obj) {
178        if (obj == this) {
179            return true;
180        }
181        if (obj instanceof Map.Entry<?, ?>) {
182            final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
183            return Objects.equals(getKey(), other.getKey())
184                    && Objects.equals(getValue(), other.getValue());
185        }
186        return false;
187    }
188
189    /**
190     * Gets the key from this pair.
191     *
192     * <p>This method implements the {@code Map.Entry} interface returning the
193     * left element as the key.</p>
194     *
195     * @return the left element as the key, may be null.
196     */
197    @Override
198    public final L getKey() {
199        return getLeft();
200    }
201
202    /**
203     * Gets the left element from this pair.
204     *
205     * <p>When treated as a key-value pair, this is the key.</p>
206     *
207     * @return the left element, may be null.
208     */
209    public abstract L getLeft();
210
211    /**
212     * Gets the right element from this pair.
213     *
214     * <p>When treated as a key-value pair, this is the value.</p>
215     *
216     * @return the right element, may be null.
217     */
218    public abstract R getRight();
219
220    /**
221     * Gets the value from this pair.
222     *
223     * <p>This method implements the {@code Map.Entry} interface returning the
224     * right element as the value.</p>
225     *
226     * @return the right element as the value, may be null.
227     */
228    @Override
229    public R getValue() {
230        return getRight();
231    }
232
233    /**
234     * Returns a suitable hash code.
235     * <p>
236     * The hash code follows the definition in {@code Map.Entry}.
237     * </p>
238     *
239     * @return the hash code.
240     */
241    @Override
242    public int hashCode() {
243        // See Map.Entry API specification
244        return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
245    }
246
247    /**
248     * Returns a String representation of this pair using the format {@code (left,right)}.
249     *
250     * @return a string describing this object, not null.
251     */
252    @Override
253    public String toString() {
254        return "(" + getLeft() + ',' + getRight() + ')';
255    }
256
257    /**
258     * Formats the receiver using the given format.
259     *
260     * <p>
261     * 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$s} for
262     * the left element (key) and {@code %2$s} for the right element (value).
263     * </p>
264     *
265     * @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null.
266     * @return the formatted string, not null.
267     * @see String#format(String, Object...)
268     */
269    public String toString(final String format) {
270        return String.format(format, getLeft(), getRight());
271    }
272
273}