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.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 *
041 * @since 3.0
042 */
043public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {
044
045    /** Serialization version */
046    private static final long serialVersionUID = 4954918890077093841L;
047
048    /**
049     * An empty array.
050     * <p>
051     * Consider using {@link #emptyArray()} to avoid generics warnings.
052     * </p>
053     *
054     * @since 3.10.
055     */
056    public static final Pair<?, ?>[] EMPTY_ARRAY = {};
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> Pair<L, R>[] emptyArray() {
069        return (Pair<L, R>[]) EMPTY_ARRAY;
070    }
071
072    /**
073     * Creates an immutable pair of two objects inferring the generic types.
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     * @param right  the right element, may be null
082     * @return a pair formed from the two parameters, not null
083     */
084    public static <L, R> Pair<L, R> of(final L left, final R right) {
085        return ImmutablePair.of(left, right);
086    }
087
088    /**
089     * Creates an immutable pair from a map entry.
090     *
091     * <p>This factory allows the pair to be created using inference to
092     * obtain the generic types.</p>
093     *
094     * @param <L> the left element type
095     * @param <R> the right element type
096     * @param pair the map entry.
097     * @return a pair formed from the map entry
098     * @since 3.10
099     */
100    public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
101        return ImmutablePair.of(pair);
102    }
103
104    /**
105     * Creates an immutable pair of two non-null objects inferring the generic types.
106     *
107     * <p>This factory allows the pair to be created using inference to
108     * obtain the generic types.</p>
109     *
110     * @param <L> the left element type
111     * @param <R> the right element type
112     * @param left  the left element, may not be null
113     * @param right  the right element, may not  be null
114     * @return a pair formed from the two parameters, not null
115     * @throws NullPointerException if any input is null
116     * @since 3.13.0
117     */
118    public static <L, R> Pair<L, R> ofNonNull(final L left, final R right) {
119        return ImmutablePair.ofNonNull(left, right);
120    }
121
122    /**
123     * Constructs a new instance.
124     */
125    public Pair() {
126        // empty
127    }
128
129    /**
130     * Accepts this key and value as arguments to the given consumer.
131     *
132     * @param <E> The kind of thrown exception or error.
133     * @param consumer the consumer to call.
134     * @throws E Thrown when the consumer fails.
135     * @since 3.13.0
136     */
137    public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
138        consumer.accept(getKey(), getValue());
139    }
140
141    /**
142     * Applies this key and value as arguments to the given function.
143     *
144     * @param <V> The function return type.
145     * @param <E> The kind of thrown exception or error.
146     * @param function the consumer to call.
147     * @return the function's return value.
148     * @throws E Thrown when the consumer fails.
149     * @since 3.13.0
150     */
151    public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
152        return function.apply(getKey(), getValue());
153    }
154
155    /**
156     * Compares the pair based on the left element followed by the right element.
157     * The types must be {@link Comparable}.
158     *
159     * @param other  the other pair, not null
160     * @return negative if this is less, zero if equal, positive if greater
161     */
162    @Override
163    public int compareTo(final Pair<L, R> other) {
164      return new CompareToBuilder().append(getLeft(), other.getLeft())
165              .append(getRight(), other.getRight()).toComparison();
166    }
167
168    /**
169     * Compares this pair to another based on the two elements.
170     *
171     * @param obj  the object to compare to, null returns false
172     * @return true if the elements of the pair are equal
173     */
174    @Override
175    public boolean equals(final Object obj) {
176        if (obj == this) {
177            return true;
178        }
179        if (obj instanceof Map.Entry<?, ?>) {
180            final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
181            return Objects.equals(getKey(), other.getKey())
182                    && Objects.equals(getValue(), other.getValue());
183        }
184        return false;
185    }
186
187    /**
188     * Gets the key from this pair.
189     *
190     * <p>This method implements the {@code Map.Entry} interface returning the
191     * left element as the key.</p>
192     *
193     * @return the left element as the key, may be null
194     */
195    @Override
196    public final L getKey() {
197        return getLeft();
198    }
199
200    /**
201     * Gets the left element from this pair.
202     *
203     * <p>When treated as a key-value pair, this is the key.</p>
204     *
205     * @return the left element, may be null
206     */
207    public abstract L getLeft();
208
209    /**
210     * Gets the right element from this pair.
211     *
212     * <p>When treated as a key-value pair, this is the value.</p>
213     *
214     * @return the right element, may be null
215     */
216    public abstract R getRight();
217
218    /**
219     * Gets the value from this pair.
220     *
221     * <p>This method implements the {@code Map.Entry} interface returning the
222     * right element as the value.</p>
223     *
224     * @return the right element as the value, may be null
225     */
226    @Override
227    public R getValue() {
228        return getRight();
229    }
230
231    /**
232     * Returns a suitable hash code.
233     * The hash code follows the definition in {@code Map.Entry}.
234     *
235     * @return the hash code
236     */
237    @Override
238    public int hashCode() {
239        // see Map.Entry API specification
240        return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
241    }
242
243    /**
244     * Returns a String representation of this pair using the format {@code ($left,$right)}.
245     *
246     * @return a string describing this object, not null
247     */
248    @Override
249    public String toString() {
250        return "(" + getLeft() + ',' + getRight() + ')';
251    }
252
253    /**
254     * Formats the receiver using the given format.
255     *
256     * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
257     * be used to embed the left and right elements. Use {@code %1$s} for the left
258     * element (key) and {@code %2$s} for the right element (value).
259     * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
260     *
261     * @param format  the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
262     * @return the formatted string, not null
263     */
264    public String toString(final String format) {
265        return String.format(format, getLeft(), getRight());
266    }
267
268}