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25
26/*
27 * This file is available under and governed by the GNU General Public
28 * License version 2 only, as published by the Free Software Foundation.
29 * However, the following notice accompanied the original version of this
30 * file:
31 *
32 * Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
33 *
34 * All rights reserved.
35 *
36 * Redistribution and use in source and binary forms, with or without
37 * modification, are permitted provided that the following conditions are met:
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61 */
62package java.time.temporal;
63
64import java.time.DateTimeException;
65
66/**
67 * Strategy for adjusting a temporal object.
68 * <p>
69 * Adjusters are a key tool for modifying temporal objects.
70 * They exist to externalize the process of adjustment, permitting different
71 * approaches, as per the strategy design pattern.
72 * Examples might be an adjuster that sets the date avoiding weekends, or one that
73 * sets the date to the last day of the month.
74 * <p>
75 * There are two equivalent ways of using a {@code TemporalAdjuster}.
76 * The first is to invoke the method on this interface directly.
77 * The second is to use {@link Temporal#with(TemporalAdjuster)}:
78 * <pre>
79 *   // these two lines are equivalent, but the second approach is recommended
80 *   temporal = thisAdjuster.adjustInto(temporal);
81 *   temporal = temporal.with(thisAdjuster);
82 * </pre>
83 * It is recommended to use the second approach, {@code with(TemporalAdjuster)},
84 * as it is a lot clearer to read in code.
85 * <p>
86 * The {@link TemporalAdjusters} class contains a standard set of adjusters,
87 * available as static methods.
88 * These include:
89 * <ul>
90 * <li>finding the first or last day of the month
91 * <li>finding the first day of next month
92 * <li>finding the first or last day of the year
93 * <li>finding the first day of next year
94 * <li>finding the first or last day-of-week within a month, such as "first Wednesday in June"
95 * <li>finding the next or previous day-of-week, such as "next Thursday"
96 * </ul>
97 *
98 * @implSpec
99 * This interface places no restrictions on the mutability of implementations,
100 * however immutability is strongly recommended.
101 *
102 * @see TemporalAdjusters
103 * @since 1.8
104 */
105@FunctionalInterface
106public interface TemporalAdjuster {
107
108    /**
109     * Adjusts the specified temporal object.
110     * <p>
111     * This adjusts the specified temporal object using the logic
112     * encapsulated in the implementing class.
113     * Examples might be an adjuster that sets the date avoiding weekends, or one that
114     * sets the date to the last day of the month.
115     * <p>
116     * There are two equivalent ways of using this method.
117     * The first is to invoke this method directly.
118     * The second is to use {@link Temporal#with(TemporalAdjuster)}:
119     * <pre>
120     *   // these two lines are equivalent, but the second approach is recommended
121     *   temporal = thisAdjuster.adjustInto(temporal);
122     *   temporal = temporal.with(thisAdjuster);
123     * </pre>
124     * It is recommended to use the second approach, {@code with(TemporalAdjuster)},
125     * as it is a lot clearer to read in code.
126     *
127     * @implSpec
128     * The implementation must take the input object and adjust it.
129     * The implementation defines the logic of the adjustment and is responsible for
130     * documenting that logic. It may use any method on {@code Temporal} to
131     * query the temporal object and perform the adjustment.
132     * The returned object must have the same observable type as the input object
133     * <p>
134     * The input object must not be altered.
135     * Instead, an adjusted copy of the original must be returned.
136     * This provides equivalent, safe behavior for immutable and mutable temporal objects.
137     * <p>
138     * The input temporal object may be in a calendar system other than ISO.
139     * Implementations may choose to document compatibility with other calendar systems,
140     * or reject non-ISO temporal objects by {@link TemporalQueries#chronology() querying the chronology}.
141     * <p>
142     * This method may be called from multiple threads in parallel.
143     * It must be thread-safe when invoked.
144     *
145     * @param temporal  the temporal object to adjust, not null
146     * @return an object of the same observable type with the adjustment made, not null
147     * @throws DateTimeException if unable to make the adjustment
148     * @throws ArithmeticException if numeric overflow occurs
149     */
150    Temporal adjustInto(Temporal temporal);
151
152}
153