104 import jdk.internal.util.DecimalDigits;
105
106 /**
107 * A year-month in the ISO-8601 calendar system, such as {@code 2007-12}.
108 * <p>
109 * {@code YearMonth} is an immutable date-time object that represents the combination
110 * of a year and month. Any field that can be derived from a year and month, such as
111 * quarter-of-year, can be obtained.
112 * <p>
113 * This class does not store or represent a day, time or time-zone.
114 * For example, the value "October 2007" can be stored in a {@code YearMonth}.
115 * <p>
116 * The ISO-8601 calendar system is the modern civil calendar system used today
117 * in most of the world. It is equivalent to the proleptic Gregorian calendar
118 * system, in which today's rules for leap years are applied for all time.
119 * For most applications written today, the ISO-8601 rules are entirely suitable.
120 * However, any application that makes use of historical dates, and requires them
121 * to be accurate will find the ISO-8601 approach unsuitable.
122 * <p>
123 * This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
124 * class; programmers should treat instances that are
125 * {@linkplain #equals(Object) equal} as interchangeable and should not
126 * use instances for synchronization, or unpredictable behavior may
127 * occur. For example, in a future release, synchronization may fail.
128 * The {@code equals} method should be used for comparisons.
129 *
130 * @implSpec
131 * This class is immutable and thread-safe.
132 *
133 * @since 1.8
134 */
135 @jdk.internal.ValueBased
136 public final class YearMonth
137 implements Temporal, TemporalAdjuster, Comparable<YearMonth>, Serializable {
138
139 /**
140 * Serialization version.
141 */
142 @java.io.Serial
143 private static final long serialVersionUID = 4183400860270640070L;
144
145 /**
146 * For backward compatibility of the serialized {@code YearMonth.class} object,
147 * explicitly declare the types of the serialized fields as defined in Java SE 8.
148 * Instances of {@code YearMonth} are serialized using the dedicated
149 * serialized form by {@code writeReplace}.
150 * @serialField year int The year.
151 * @serialField month int The month-of-year.
152 */
153 @java.io.Serial
154 private static final ObjectStreamField[] serialPersistentFields = {
155 new ObjectStreamField("year", int.class),
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104 import jdk.internal.util.DecimalDigits;
105
106 /**
107 * A year-month in the ISO-8601 calendar system, such as {@code 2007-12}.
108 * <p>
109 * {@code YearMonth} is an immutable date-time object that represents the combination
110 * of a year and month. Any field that can be derived from a year and month, such as
111 * quarter-of-year, can be obtained.
112 * <p>
113 * This class does not store or represent a day, time or time-zone.
114 * For example, the value "October 2007" can be stored in a {@code YearMonth}.
115 * <p>
116 * The ISO-8601 calendar system is the modern civil calendar system used today
117 * in most of the world. It is equivalent to the proleptic Gregorian calendar
118 * system, in which today's rules for leap years are applied for all time.
119 * For most applications written today, the ISO-8601 rules are entirely suitable.
120 * However, any application that makes use of historical dates, and requires them
121 * to be accurate will find the ISO-8601 approach unsuitable.
122 * <p>
123 * This is a <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>
124 * class; programmers should treat instances that are {@linkplain #equals(Object) equal}
125 * as interchangeable and should not use instances for synchronization, mutexes, or
126 * with {@linkplain java.lang.ref.Reference object references}.
127 *
128 * <div class="preview-block">
129 * <div class="preview-comment">
130 * When preview features are enabled, {@code YearMonth} is a {@linkplain Class#isValue value class}.
131 * Use of value class instances for synchronization, mutexes, or with
132 * {@linkplain java.lang.ref.Reference object references} result in
133 * {@link IdentityException}.
134 * </div>
135 * </div>
136 *
137 * @implSpec
138 * This class is immutable and thread-safe.
139 *
140 * @since 1.8
141 */
142 @jdk.internal.ValueBased
143 @jdk.internal.MigratedValueClass
144 public final class YearMonth
145 implements Temporal, TemporalAdjuster, Comparable<YearMonth>, Serializable {
146
147 /**
148 * Serialization version.
149 */
150 @java.io.Serial
151 private static final long serialVersionUID = 4183400860270640070L;
152
153 /**
154 * For backward compatibility of the serialized {@code YearMonth.class} object,
155 * explicitly declare the types of the serialized fields as defined in Java SE 8.
156 * Instances of {@code YearMonth} are serialized using the dedicated
157 * serialized form by {@code writeReplace}.
158 * @serialField year int The year.
159 * @serialField month int The month-of-year.
160 */
161 @java.io.Serial
162 private static final ObjectStreamField[] serialPersistentFields = {
163 new ObjectStreamField("year", int.class),
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