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

import java.io.Serializable;
import java.util.Map;
import java.util.Objects;

import org.apache.commons.lang3.builder.CompareToBuilder;

/**
 * 

A pair consisting of two elements.

* *

This class is an abstract implementation defining the basic API. * It refers to the elements as 'left' and 'right'. It also implements the * {@code Map.Entry} interface where the key is 'left' and the value is 'right'.

* *

Subclass implementations may be mutable or immutable. * However, there is no restriction on the type of the stored objects that may be stored. * If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.

* * @param the left element type * @param the right element type * * @since 3.0 */ public abstract class Pair implements Map.Entry, Comparable>, Serializable { private static final class PairAdapter extends Pair { private static final long serialVersionUID = 1L; @Override public L getLeft() { return null; } @Override public R getRight() { return null; } @Override public R setValue(final R value) { return null; } } /** Serialization version */ private static final long serialVersionUID = 4954918890077093841L; /** * An empty array. *

* Consider using {@link #emptyArray()} to avoid generics warnings. *

* * @since 3.10. */ public static final Pair[] EMPTY_ARRAY = new PairAdapter[0]; /** * Returns the empty array singleton that can be assigned without compiler warning. * * @param the left element type * @param the right element type * @return the empty array singleton that can be assigned without compiler warning. * * @since 3.10. */ @SuppressWarnings("unchecked") public static Pair[] emptyArray() { return (Pair[]) EMPTY_ARRAY; } /** *

Creates an immutable pair of two objects inferring the generic types.

* *

This factory allows the pair to be created using inference to * obtain the generic types.

* * @param the left element type * @param the right element type * @param left the left element, may be null * @param right the right element, may be null * @return a pair formed from the two parameters, not null */ public static Pair of(final L left, final R right) { return ImmutablePair.of(left, right); } /** *

Creates an immutable pair from an existing pair.

* *

This factory allows the pair to be created using inference to * obtain the generic types.

* * @param the left element type * @param the right element type * @param pair the existing pair. * @return a pair formed from the two parameters, not null * @since 3.10 */ public static Pair of(final Map.Entry pair) { return ImmutablePair.of(pair); } //----------------------------------------------------------------------- /** *

Compares the pair based on the left element followed by the right element. * The types must be {@code Comparable}.

* * @param other the other pair, not null * @return negative if this is less, zero if equal, positive if greater */ @Override public int compareTo(final Pair other) { return new CompareToBuilder().append(getLeft(), other.getLeft()) .append(getRight(), other.getRight()).toComparison(); } /** *

Compares this pair to another based on the two elements.

* * @param obj the object to compare to, null returns false * @return true if the elements of the pair are equal */ @Override public boolean equals(final Object obj) { if (obj == this) { return true; } if (obj instanceof Map.Entry) { final Map.Entry other = (Map.Entry) obj; return Objects.equals(getKey(), other.getKey()) && Objects.equals(getValue(), other.getValue()); } return false; } /** *

Gets the key from this pair.

* *

This method implements the {@code Map.Entry} interface returning the * left element as the key.

* * @return the left element as the key, may be null */ @Override public final L getKey() { return getLeft(); } //----------------------------------------------------------------------- /** *

Gets the left element from this pair.

* *

When treated as a key-value pair, this is the key.

* * @return the left element, may be null */ public abstract L getLeft(); /** *

Gets the right element from this pair.

* *

When treated as a key-value pair, this is the value.

* * @return the right element, may be null */ public abstract R getRight(); /** *

Gets the value from this pair.

* *

This method implements the {@code Map.Entry} interface returning the * right element as the value.

* * @return the right element as the value, may be null */ @Override public R getValue() { return getRight(); } /** *

Returns a suitable hash code. * The hash code follows the definition in {@code Map.Entry}.

* * @return the hash code */ @Override public int hashCode() { // see Map.Entry API specification return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue()); } /** *

Returns a String representation of this pair using the format {@code ($left,$right)}.

* * @return a string describing this object, not null */ @Override public String toString() { return "(" + getLeft() + ',' + getRight() + ')'; } /** *

Formats the receiver using the given format.

* *

This uses {@link java.util.Formattable} to perform the formatting. Two variables may * be used to embed the left and right elements. Use {@code %1$s} for the left * element (key) and {@code %2$s} for the right element (value). * The default format used by {@code toString()} is {@code (%1$s,%2$s)}.

* * @param format the format string, optionally containing {@code %1$s} and {@code %2$s}, not null * @return the formatted string, not null */ public String toString(final String format) { return String.format(format, getLeft(), getRight()); } }




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