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    1   /*
    2    * Copyright (c) 2003, 2009, 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.Serializable;
   29   import java.io.IOException;
   30   import java.io.InvalidObjectException;
   31   import java.io.ObjectInputStream;
   32   import java.io.ObjectStreamException;
   33   
   34   /**
   35    * This is the common base class of all Java language enumeration types.
   36    *
   37    * More information about enums, including descriptions of the
   38    * implicitly declared methods synthesized by the compiler, can be
   39    * found in section 8.9 of
   40    * <cite>The Java&trade; Language Specification</cite>.
   41    *
   42    * <p> Note that when using an enumeration type as the type of a set
   43    * or as the type of the keys in a map, specialized and efficient
   44    * {@linkplain java.util.EnumSet set} and {@linkplain
   45    * java.util.EnumMap map} implementations are available.
   46    *
   47    * @param <E> The enum type subclass
   48    * @author  Josh Bloch
   49    * @author  Neal Gafter
   50    * @see     Class#getEnumConstants()
   51    * @see     java.util.EnumSet
   52    * @see     java.util.EnumMap
   53    * @since   1.5
   54    */
   55   public abstract class Enum<E extends Enum<E>>
   56           implements Comparable<E>, Serializable {
   57       /**
   58        * The name of this enum constant, as declared in the enum declaration.
   59        * Most programmers should use the {@link #toString} method rather than
   60        * accessing this field.
   61        */
   62       private final String name;
   63   
   64       /**
   65        * Returns the name of this enum constant, exactly as declared in its
   66        * enum declaration.
   67        *
   68        * <b>Most programmers should use the {@link #toString} method in
   69        * preference to this one, as the toString method may return
   70        * a more user-friendly name.</b>  This method is designed primarily for
   71        * use in specialized situations where correctness depends on getting the
   72        * exact name, which will not vary from release to release.
   73        *
   74        * @return the name of this enum constant
   75        */
   76       public final String name() {
   77           return name;
   78       }
   79   
   80       /**
   81        * The ordinal of this enumeration constant (its position
   82        * in the enum declaration, where the initial constant is assigned
   83        * an ordinal of zero).
   84        *
   85        * Most programmers will have no use for this field.  It is designed
   86        * for use by sophisticated enum-based data structures, such as
   87        * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
   88        */
   89       private final int ordinal;
   90   
   91       /**
   92        * Returns the ordinal of this enumeration constant (its position
   93        * in its enum declaration, where the initial constant is assigned
   94        * an ordinal of zero).
   95        *
   96        * Most programmers will have no use for this method.  It is
   97        * designed for use by sophisticated enum-based data structures, such
   98        * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
   99        *
  100        * @return the ordinal of this enumeration constant
  101        */
  102       public final int ordinal() {
  103           return ordinal;
  104       }
  105   
  106       /**
  107        * Sole constructor.  Programmers cannot invoke this constructor.
  108        * It is for use by code emitted by the compiler in response to
  109        * enum type declarations.
  110        *
  111        * @param name - The name of this enum constant, which is the identifier
  112        *               used to declare it.
  113        * @param ordinal - The ordinal of this enumeration constant (its position
  114        *         in the enum declaration, where the initial constant is assigned
  115        *         an ordinal of zero).
  116        */
  117       protected Enum(String name, int ordinal) {
  118           this.name = name;
  119           this.ordinal = ordinal;
  120       }
  121   
  122       /**
  123        * Returns the name of this enum constant, as contained in the
  124        * declaration.  This method may be overridden, though it typically
  125        * isn't necessary or desirable.  An enum type should override this
  126        * method when a more "programmer-friendly" string form exists.
  127        *
  128        * @return the name of this enum constant
  129        */
  130       public String toString() {
  131           return name;
  132       }
  133   
  134       /**
  135        * Returns true if the specified object is equal to this
  136        * enum constant.
  137        *
  138        * @param other the object to be compared for equality with this object.
  139        * @return  true if the specified object is equal to this
  140        *          enum constant.
  141        */
  142       public final boolean equals(Object other) {
  143           return this==other;
  144       }
  145   
  146       /**
  147        * Returns a hash code for this enum constant.
  148        *
  149        * @return a hash code for this enum constant.
  150        */
  151       public final int hashCode() {
  152           return super.hashCode();
  153       }
  154   
  155       /**
  156        * Throws CloneNotSupportedException.  This guarantees that enums
  157        * are never cloned, which is necessary to preserve their "singleton"
  158        * status.
  159        *
  160        * @return (never returns)
  161        */
  162       protected final Object clone() throws CloneNotSupportedException {
  163           throw new CloneNotSupportedException();
  164       }
  165   
  166       /**
  167        * Compares this enum with the specified object for order.  Returns a
  168        * negative integer, zero, or a positive integer as this object is less
  169        * than, equal to, or greater than the specified object.
  170        *
  171        * Enum constants are only comparable to other enum constants of the
  172        * same enum type.  The natural order implemented by this
  173        * method is the order in which the constants are declared.
  174        */
  175       public final int compareTo(E o) {
  176           Enum other = (Enum)o;
  177           Enum self = this;
  178           if (self.getClass() != other.getClass() && // optimization
  179               self.getDeclaringClass() != other.getDeclaringClass())
  180               throw new ClassCastException();
  181           return self.ordinal - other.ordinal;
  182       }
  183   
  184       /**
  185        * Returns the Class object corresponding to this enum constant's
  186        * enum type.  Two enum constants e1 and  e2 are of the
  187        * same enum type if and only if
  188        *   e1.getDeclaringClass() == e2.getDeclaringClass().
  189        * (The value returned by this method may differ from the one returned
  190        * by the {@link Object#getClass} method for enum constants with
  191        * constant-specific class bodies.)
  192        *
  193        * @return the Class object corresponding to this enum constant's
  194        *     enum type
  195        */
  196       public final Class<E> getDeclaringClass() {
  197           Class clazz = getClass();
  198           Class zuper = clazz.getSuperclass();
  199           return (zuper == Enum.class) ? clazz : zuper;
  200       }
  201   
  202       /**
  203        * Returns the enum constant of the specified enum type with the
  204        * specified name.  The name must match exactly an identifier used
  205        * to declare an enum constant in this type.  (Extraneous whitespace
  206        * characters are not permitted.)
  207        *
  208        * <p>Note that for a particular enum type {@code T}, the
  209        * implicitly declared {@code public static T valueOf(String)}
  210        * method on that enum may be used instead of this method to map
  211        * from a name to the corresponding enum constant.  All the
  212        * constants of an enum type can be obtained by calling the
  213        * implicit {@code public static T[] values()} method of that
  214        * type.
  215        *
  216        * @param <T> The enum type whose constant is to be returned
  217        * @param enumType the {@code Class} object of the enum type from which
  218        *      to return a constant
  219        * @param name the name of the constant to return
  220        * @return the enum constant of the specified enum type with the
  221        *      specified name
  222        * @throws IllegalArgumentException if the specified enum type has
  223        *         no constant with the specified name, or the specified
  224        *         class object does not represent an enum type
  225        * @throws NullPointerException if {@code enumType} or {@code name}
  226        *         is null
  227        * @since 1.5
  228        */
  229       public static <T extends Enum<T>> T valueOf(Class<T> enumType,
  230                                                   String name) {
  231           T result = enumType.enumConstantDirectory().get(name);
  232           if (result != null)
  233               return result;
  234           if (name == null)
  235               throw new NullPointerException("Name is null");
  236           throw new IllegalArgumentException(
  237               "No enum constant " + enumType.getCanonicalName() + "." + name);
  238       }
  239   
  240       /**
  241        * enum classes cannot have finalize methods.
  242        */
  243       protected final void finalize() { }
  244   
  245       /**
  246        * prevent default deserialization
  247        */
  248       private void readObject(ObjectInputStream in) throws IOException,
  249           ClassNotFoundException {
  250           throw new InvalidObjectException("can't deserialize enum");
  251       }
  252   
  253       private void readObjectNoData() throws ObjectStreamException {
  254           throw new InvalidObjectException("can't deserialize enum");
  255       }
  256   }

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