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     * @param <L> the left element type.
074     * @param <R> the right element type.
075     * @param left  the left element, may be null.
076     * @param right  the right element, may be null.
077     * @return an immutable pair formed from the two parameters, not null.
078     */
079    public static <L, R> Pair<L, R> of(final L left, final R right) {
080        return ImmutablePair.of(left, right);
081    }
082
083    /**
084     * Creates an immutable pair from a map entry.
085     *
086     * @param <L> the left element type.
087     * @param <R> the right element type.
088     * @param pair the map entry.
089     * @return an immutable pair formed from the map entry.
090     * @since 3.10
091     */
092    public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
093        return ImmutablePair.of(pair);
094    }
095
096    /**
097     * Creates an immutable pair of two non-null objects inferring the generic types.
098     *
099     * @param <L> the left element type.
100     * @param <R> the right element type.
101     * @param left  the left element, may not be null.
102     * @param right  the right element, may not  be null.
103     * @return an immutable pair formed from the two parameters, not null.
104     * @throws NullPointerException if any input is null.
105     * @since 3.13.0
106     */
107    public static <L, R> Pair<L, R> ofNonNull(final L left, final R right) {
108        return ImmutablePair.ofNonNull(left, right);
109    }
110
111    /**
112     * Constructs a new instance.
113     */
114    public Pair() {
115        // empty
116    }
117
118    /**
119     * Accepts this key and value as arguments to the given consumer.
120     *
121     * @param <E> The kind of thrown exception or error.
122     * @param consumer the consumer to call.
123     * @throws E Thrown when the consumer fails.
124     * @since 3.13.0
125     */
126    public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
127        consumer.accept(getKey(), getValue());
128    }
129
130    /**
131     * Applies this key and value as arguments to the given function.
132     *
133     * @param <V> The function return type.
134     * @param <E> The kind of thrown exception or error.
135     * @param function the consumer to call.
136     * @return the function's return value.
137     * @throws E Thrown when the consumer fails.
138     * @since 3.13.0
139     */
140    public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
141        return function.apply(getKey(), getValue());
142    }
143
144    /**
145     * Compares the pair based on the left element followed by the right element.
146     * The types must be {@link Comparable}.
147     *
148     * @param other  the other pair, not null.
149     * @return negative if this is less, zero if equal, positive if greater.
150     */
151    @Override
152    public int compareTo(final Pair<L, R> other) {
153        // @formatter:off
154        return new CompareToBuilder()
155            .append(getLeft(), other.getLeft())
156            .append(getRight(), other.getRight())
157            .toComparison();
158        // @formatter:on
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     * <p>
227     * The hash code follows the definition in {@code Map.Entry}.
228     * </p>
229     *
230     * @return the hash code.
231     */
232    @Override
233    public int hashCode() {
234        // See Map.Entry API specification
235        return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
236    }
237
238    /**
239     * Returns a String representation of this pair using the format {@code (left,right)}.
240     *
241     * @return a string describing this object, not null.
242     */
243    @Override
244    public String toString() {
245        return "(" + getLeft() + ',' + getRight() + ')';
246    }
247
248    /**
249     * Formats the receiver using the given format.
250     *
251     * <p>
252     * 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$s} for
253     * the left element (key) and {@code %2$s} for the right element (value).
254     * </p>
255     *
256     * @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null.
257     * @return the formatted string, not null.
258     * @see String#format(String, Object...)
259     */
260    public String toString(final String format) {
261        return String.format(format, getLeft(), getRight());
262    }
263
264}