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<E> 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     @SuppressWarnings("unchecked")
 197     public final Class<E> getDeclaringClass() {
 198         Class<?> clazz = getClass();
 199         Class<?> zuper = clazz.getSuperclass();
 200         return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;
 201     }
 202 
 203     /**
 204      * Returns the enum constant of the specified enum type with the
 205      * specified name.  The name must match exactly an identifier used
 206      * to declare an enum constant in this type.  (Extraneous whitespace
 207      * characters are not permitted.)
 208      *
 209      * <p>Note that for a particular enum type {@code T}, the
 210      * implicitly declared {@code public static T valueOf(String)}
 211      * method on that enum may be used instead of this method to map
 212      * from a name to the corresponding enum constant.  All the
 213      * constants of an enum type can be obtained by calling the
 214      * implicit {@code public static T[] values()} method of that
 215      * type.
 216      *
 217      * @param <T> The enum type whose constant is to be returned
 218      * @param enumType the {@code Class} object of the enum type from which
 219      *      to return a constant
 220      * @param name the name of the constant to return
 221      * @return the enum constant of the specified enum type with the
 222      *      specified name
 223      * @throws IllegalArgumentException if the specified enum type has
 224      *         no constant with the specified name, or the specified
 225      *         class object does not represent an enum type
 226      * @throws NullPointerException if {@code enumType} or {@code name}
 227      *         is null
 228      * @since 1.5
 229      */
 230     public static <T extends Enum<T>> T valueOf(Class<T> enumType,
 231                                                 String name) {
 232         T result = enumType.enumConstantDirectory().get(name);
 233         if (result != null)
 234             return result;
 235         if (name == null)
 236             throw new NullPointerException("Name is null");
 237         throw new IllegalArgumentException(
 238             "No enum constant " + enumType.getCanonicalName() + "." + name);
 239     }
 240 
 241     /**
 242      * enum classes cannot have finalize methods.
 243      */
 244     protected final void finalize() { }
 245 
 246     /**
 247      * prevent default deserialization
 248      */
 249     private void readObject(ObjectInputStream in) throws IOException,
 250         ClassNotFoundException {
 251         throw new InvalidObjectException("can't deserialize enum");
 252     }
 253 
 254     private void readObjectNoData() throws ObjectStreamException {
 255         throw new InvalidObjectException("can't deserialize enum");
 256     }
 257 }