Pair.java

  1. /*
  2.  * Licensed to the Apache Software Foundation (ASF) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * The ASF licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *      https://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.apache.commons.lang3.tuple;

  19. import java.io.Serializable;
  20. import java.util.Map;
  21. import java.util.Objects;

  23. import org.apache.commons.lang3.builder.CompareToBuilder;
  24. import org.apache.commons.lang3.function.FailableBiConsumer;
  25. import org.apache.commons.lang3.function.FailableBiFunction;

  27. /**
  28.  * A pair consisting of two elements.
  29.  *
  30.  * <p>This class is an abstract implementation defining the basic API.
  31.  * It refers to the elements as 'left' and 'right'. It also implements the
  32.  * {@code Map.Entry} interface where the key is 'left' and the value is 'right'.</p>
  33.  *
  34.  * <p>Subclass implementations may be mutable or immutable.
  35.  * However, there is no restriction on the type of the stored objects that may be stored.
  36.  * If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.</p>
  37.  *
  38.  * @param <L> the left element type.
  39.  * @param <R> the right element type.
  40.  * @since 3.0
  41.  */
  42. public abstract class Pair<L, R> implements Map.Entry<L, R>, Comparable<Pair<L, R>>, Serializable {

  44.     /** Serialization version */
  45.     private static final long serialVersionUID = 4954918890077093841L;

  47.     /**
  48.      * An empty array.
  49.      * <p>
  50.      * Consider using {@link #emptyArray()} to avoid generics warnings.
  51.      * </p>
  52.      *
  53.      * @since 3.10
  54.      */
  55.     public static final Pair<?, ?>[] EMPTY_ARRAY = {};

  57.     /**
  58.      * Returns the empty array singleton that can be assigned without compiler warning.
  59.      *
  60.      * @param <L> the left element type.
  61.      * @param <R> the right element type.
  62.      * @return the empty array singleton that can be assigned without compiler warning.
  63.      * @since 3.10
  64.      */
  65.     @SuppressWarnings("unchecked")
  66.     public static <L, R> Pair<L, R>[] emptyArray() {
  67.         return (Pair<L, R>[]) EMPTY_ARRAY;
  68.     }

  70.     /**
  71.      * Creates an immutable pair of two objects inferring the generic types.
  72.      *
  73.      * <p>This factory allows the pair to be created using inference to
  74.      * obtain the generic types.</p>
  75.      *
  76.      * @param <L> the left element type.
  77.      * @param <R> the right element type.
  78.      * @param left  the left element, may be null.
  79.      * @param right  the right element, may be null.
  80.      * @return a pair formed from the two parameters, not null.
  81.      */
  82.     public static <L, R> Pair<L, R> of(final L left, final R right) {
  83.         return ImmutablePair.of(left, right);
  84.     }

  86.     /**
  87.      * Creates an immutable pair from a map entry.
  88.      *
  89.      * <p>This factory allows the pair to be created using inference to
  90.      * obtain the generic types.</p>
  91.      *
  92.      * @param <L> the left element type.
  93.      * @param <R> the right element type.
  94.      * @param pair the map entry.
  95.      * @return a pair formed from the map entry.
  96.      * @since 3.10
  97.      */
  98.     public static <L, R> Pair<L, R> of(final Map.Entry<L, R> pair) {
  99.         return ImmutablePair.of(pair);
  100.     }

  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.     }

  120.     /**
  121.      * Constructs a new instance.
  122.      */
  123.     public Pair() {
  124.         // empty
  125.     }

  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.     }

  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.     }

  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.     }

  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.     }

  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.     }

  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();

  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();

  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.     }

  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.     }

  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.     }

  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.     }

  273. }
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