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     * Accepts this key and value as arguments to the given consumer.
124     *
125     * @param <E> The kind of thrown exception or error.
126     * @param consumer the consumer to call.
127     * @throws E Thrown when the consumer fails.
128     * @since 3.13.0
129     */
130    public <E extends Throwable> void accept(final FailableBiConsumer<L, R, E> consumer) throws E {
131        consumer.accept(getKey(), getValue());
132    }
133
134    /**
135     * Applies this key and value as arguments to the given function.
136     *
137     * @param <V> The function return type.
138     * @param <E> The kind of thrown exception or error.
139     * @param function the consumer to call.
140     * @return the function's return value.
141     * @throws E Thrown when the consumer fails.
142     * @since 3.13.0
143     */
144    public <V, E extends Throwable> V apply(final FailableBiFunction<L, R, V, E> function) throws E {
145        return function.apply(getKey(), getValue());
146    }
147
148    /**
149     * Compares the pair based on the left element followed by the right element.
150     * The types must be {@link Comparable}.
151     *
152     * @param other  the other pair, not null
153     * @return negative if this is less, zero if equal, positive if greater
154     */
155    @Override
156    public int compareTo(final Pair<L, R> other) {
157      return new CompareToBuilder().append(getLeft(), other.getLeft())
158              .append(getRight(), other.getRight()).toComparison();
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     * The hash code follows the definition in {@code Map.Entry}.
227     *
228     * @return the hash code
229     */
230    @Override
231    public int hashCode() {
232        // see Map.Entry API specification
233        return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
234    }
235
236    /**
237     * Returns a String representation of this pair using the format {@code ($left,$right)}.
238     *
239     * @return a string describing this object, not null
240     */
241    @Override
242    public String toString() {
243        return "(" + getLeft() + ',' + getRight() + ')';
244    }
245
246    /**
247     * Formats the receiver using the given format.
248     *
249     * <p>This uses {@link java.util.Formattable} to perform the formatting. Two variables may
250     * be used to embed the left and right elements. Use {@code %1$s} for the left
251     * element (key) and {@code %2$s} for the right element (value).
252     * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.</p>
253     *
254     * @param format  the format string, optionally containing {@code %1$s} and {@code %2$s}, not null
255     * @return the formatted string, not null
256     */
257    public String toString(final String format) {
258        return String.format(format, getLeft(), getRight());
259    }
260
261}