1 /*
   2  * Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 import java.io.IOException;
  29 import java.io.InvalidObjectException;
  30 import java.io.ObjectInputStream;
  31 import java.io.ObjectStreamException;
  32 import java.io.Serializable;
  33 import java.lang.constant.ClassDesc;
  34 import java.lang.constant.Constable;
  35 import java.lang.constant.ConstantDescs;
  36 import java.lang.constant.DynamicConstantDesc;
  37 import java.lang.invoke.MethodHandles;
  38 import java.util.Optional;
  39 
  40 import static java.util.Objects.requireNonNull;
  41 
  42 /**
  43  * This is the common base class of all Java language enumeration types.
  44  *
  45  * More information about enums, including descriptions of the
  46  * implicitly declared methods synthesized by the compiler, can be
  47  * found in section 8.9 of
  48  * <cite>The Java&trade; Language Specification</cite>.
  49  *
  50  * <p> Note that when using an enumeration type as the type of a set
  51  * or as the type of the keys in a map, specialized and efficient
  52  * {@linkplain java.util.EnumSet set} and {@linkplain
  53  * java.util.EnumMap map} implementations are available.
  54  *
  55  * @param <E> The enum type subclass
  56  * @serial exclude
  57  * @author  Josh Bloch
  58  * @author  Neal Gafter
  59  * @see     Class#getEnumConstants()
  60  * @see     java.util.EnumSet
  61  * @see     java.util.EnumMap
  62  * @since   1.5
  63  */
  64 @SuppressWarnings("serial") // No serialVersionUID needed due to
  65                             // special-casing of enum types.
  66 public abstract class Enum<E extends Enum<E>>
  67         implements Constable, Comparable<E>, Serializable {
  68     /**
  69      * The name of this enum constant, as declared in the enum declaration.
  70      * Most programmers should use the {@link #toString} method rather than
  71      * accessing this field.
  72      */
  73     private final String name;
  74 
  75     /**
  76      * Returns the name of this enum constant, exactly as declared in its
  77      * enum declaration.
  78      *
  79      * <b>Most programmers should use the {@link #toString} method in
  80      * preference to this one, as the toString method may return
  81      * a more user-friendly name.</b>  This method is designed primarily for
  82      * use in specialized situations where correctness depends on getting the
  83      * exact name, which will not vary from release to release.
  84      *
  85      * @return the name of this enum constant
  86      */
  87     public final String name() {
  88         return name;
  89     }
  90 
  91     /**
  92      * The ordinal of this enumeration constant (its position
  93      * in the enum declaration, where the initial constant is assigned
  94      * an ordinal of zero).
  95      *
  96      * Most programmers will have no use for this field.  It is designed
  97      * for use by sophisticated enum-based data structures, such as
  98      * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
  99      */
 100     private final int ordinal;
 101 
 102     /**
 103      * Returns the ordinal of this enumeration constant (its position
 104      * in its enum declaration, where the initial constant is assigned
 105      * an ordinal of zero).
 106      *
 107      * Most programmers will have no use for this method.  It is
 108      * designed for use by sophisticated enum-based data structures, such
 109      * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
 110      *
 111      * @return the ordinal of this enumeration constant
 112      */
 113     public final int ordinal() {
 114         return ordinal;
 115     }
 116 
 117     /**
 118      * Sole constructor.  Programmers cannot invoke this constructor.
 119      * It is for use by code emitted by the compiler in response to
 120      * enum type declarations.
 121      *
 122      * @param name - The name of this enum constant, which is the identifier
 123      *               used to declare it.
 124      * @param ordinal - The ordinal of this enumeration constant (its position
 125      *         in the enum declaration, where the initial constant is assigned
 126      *         an ordinal of zero).
 127      */
 128     protected Enum(String name, int ordinal) {
 129         this.name = name;
 130         this.ordinal = ordinal;
 131     }
 132 
 133     /**
 134      * Returns the name of this enum constant, as contained in the
 135      * declaration.  This method may be overridden, though it typically
 136      * isn't necessary or desirable.  An enum type should override this
 137      * method when a more "programmer-friendly" string form exists.
 138      *
 139      * @return the name of this enum constant
 140      */
 141     public String toString() {
 142         return name;
 143     }
 144 
 145     /**
 146      * Returns true if the specified object is equal to this
 147      * enum constant.
 148      *
 149      * @param other the object to be compared for equality with this object.
 150      * @return  true if the specified object is equal to this
 151      *          enum constant.
 152      */
 153     public final boolean equals(Object other) {
 154         return this==other;
 155     }
 156 
 157     /**
 158      * Returns a hash code for this enum constant.
 159      *
 160      * @return a hash code for this enum constant.
 161      */
 162     public final int hashCode() {
 163         return super.hashCode();
 164     }
 165 
 166     /**
 167      * Throws CloneNotSupportedException.  This guarantees that enums
 168      * are never cloned, which is necessary to preserve their "singleton"
 169      * status.
 170      *
 171      * @return (never returns)
 172      */
 173     protected final Object clone() throws CloneNotSupportedException {
 174         throw new CloneNotSupportedException();
 175     }
 176 
 177     /**
 178      * Compares this enum with the specified object for order.  Returns a
 179      * negative integer, zero, or a positive integer as this object is less
 180      * than, equal to, or greater than the specified object.
 181      *
 182      * Enum constants are only comparable to other enum constants of the
 183      * same enum type.  The natural order implemented by this
 184      * method is the order in which the constants are declared.
 185      */
 186     public final int compareTo(E o) {
 187         Enum<?> other = (Enum<?>)o;
 188         Enum<E> self = this;
 189         if (self.getClass() != other.getClass() && // optimization
 190             self.getDeclaringClass() != other.getDeclaringClass())
 191             throw new ClassCastException();
 192         return self.ordinal - other.ordinal;
 193     }
 194 
 195     /**
 196      * Returns the Class object corresponding to this enum constant's
 197      * enum type.  Two enum constants e1 and  e2 are of the
 198      * same enum type if and only if
 199      *   e1.getDeclaringClass() == e2.getDeclaringClass().
 200      * (The value returned by this method may differ from the one returned
 201      * by the {@link Object#getClass} method for enum constants with
 202      * constant-specific class bodies.)
 203      *
 204      * @return the Class object corresponding to this enum constant's
 205      *     enum type
 206      */
 207     @SuppressWarnings("unchecked")
 208     public final Class<E> getDeclaringClass() {
 209         Class<?> clazz = getClass();
 210         Class<?> zuper = clazz.getSuperclass();
 211         return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;
 212     }
 213 
 214     /**
 215      * Returns an enum descriptor {@code EnumDesc} for this instance, if one can be
 216      * constructed, or an empty {@link Optional} if one cannot be.
 217      *
 218      * @return An {@link Optional} containing the resulting nominal descriptor,
 219      * or an empty {@link Optional} if one cannot be constructed.
 220      * @since 12
 221      */
 222     @Override
 223     public final Optional<EnumDesc<E>> describeConstable() {
 224         return getDeclaringClass()
 225                 .describeConstable()
 226                 .map(c -> EnumDesc.of(c, name));
 227     }
 228 
 229     /**
 230      * Returns the enum constant of the specified enum type with the
 231      * specified name.  The name must match exactly an identifier used
 232      * to declare an enum constant in this type.  (Extraneous whitespace
 233      * characters are not permitted.)
 234      *
 235      * <p>Note that for a particular enum type {@code T}, the
 236      * implicitly declared {@code public static T valueOf(String)}
 237      * method on that enum may be used instead of this method to map
 238      * from a name to the corresponding enum constant.  All the
 239      * constants of an enum type can be obtained by calling the
 240      * implicit {@code public static T[] values()} method of that
 241      * type.
 242      *
 243      * @param <T> The enum type whose constant is to be returned
 244      * @param enumType the {@code Class} object of the enum type from which
 245      *      to return a constant
 246      * @param name the name of the constant to return
 247      * @return the enum constant of the specified enum type with the
 248      *      specified name
 249      * @throws IllegalArgumentException if the specified enum type has
 250      *         no constant with the specified name, or the specified
 251      *         class object does not represent an enum type
 252      * @throws NullPointerException if {@code enumType} or {@code name}
 253      *         is null
 254      * @since 1.5
 255      */
 256     public static <T extends Enum<T>> T valueOf(Class<T> enumType,
 257                                                 String name) {
 258         T result = enumType.enumConstantDirectory().get(name);
 259         if (result != null)
 260             return result;
 261         if (name == null)
 262             throw new NullPointerException("Name is null");
 263         throw new IllegalArgumentException(
 264             "No enum constant " + enumType.getCanonicalName() + "." + name);
 265     }
 266 
 267     /**
 268      * enum classes cannot have finalize methods.
 269      */
 270     @SuppressWarnings("deprecation")
 271     protected final void finalize() { }
 272 
 273     /**
 274      * prevent default deserialization
 275      */
 276     private void readObject(ObjectInputStream in) throws IOException,
 277         ClassNotFoundException {
 278         throw new InvalidObjectException("can't deserialize enum");
 279     }
 280 
 281     private void readObjectNoData() throws ObjectStreamException {
 282         throw new InvalidObjectException("can't deserialize enum");
 283     }
 284 
 285     /**
 286      * A <a href="package-summary.html#nominal">nominal descriptor</a> for an
 287      * {@code enum} constant.
 288      *
 289      * @param <E> the type of the enum constant
 290      *
 291      * @since 12
 292      */
 293     public static final class EnumDesc<E extends Enum<E>>
 294             extends DynamicConstantDesc<E> {
 295 
 296         /**
 297          * Constructs a nominal descriptor for the specified {@code enum} class and name.
 298          *
 299          * @param constantType a {@link ClassDesc} describing the {@code enum} class
 300          * @param constantName the unqualified name of the enum constant
 301          * @throws NullPointerException if any argument is null
 302          * @jvms 4.2.2 Unqualified Names
 303          */
 304         private EnumDesc(ClassDesc constantType, String constantName) {
 305             super(ConstantDescs.BSM_ENUM_CONSTANT, requireNonNull(constantName), requireNonNull(constantType));
 306         }
 307 
 308         /**
 309          * Returns a nominal descriptor for the specified {@code enum} class and name
 310          *
 311          * @param <E> the type of the enum constant
 312          * @param enumClass a {@link ClassDesc} describing the {@code enum} class
 313          * @param constantName the unqualified name of the enum constant
 314          * @return the nominal descriptor
 315          * @throws NullPointerException if any argument is null
 316          * @jvms 4.2.2 Unqualified Names
 317          * @since 12
 318          */
 319         public static<E extends Enum<E>> EnumDesc<E> of(ClassDesc enumClass,
 320                                                         String constantName) {
 321             return new EnumDesc<>(enumClass, constantName);
 322         }
 323 
 324         @Override
 325         @SuppressWarnings("unchecked")
 326         public E resolveConstantDesc(MethodHandles.Lookup lookup)
 327                 throws ReflectiveOperationException {
 328             return Enum.valueOf((Class<E>) constantType().resolveConstantDesc(lookup), constantName());
 329         }
 330 
 331         @Override
 332         public String toString() {
 333             return String.format("EnumDesc[%s.%s]", constantType().displayName(), constantName());
 334         }
 335     }
 336 }