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28 import java.io.Serializable;
29 import java.io.IOException;
32 * This is the common base class of all Java language enumeration types.
34 * More information about enums, including descriptions of the
35 * implicitly declared methods synthesized by the compiler, can be
36 * found in section 8.9 of
37 * <cite>The Java™ Language Specification</cite>.
39 * <p> Note that when using an enumeration type as the type of a set
40 * or as the type of the keys in a map, specialized and efficient
41 * {@linkplain java.util.EnumSet set} and {@linkplain
42 * java.util.EnumMap map} implementations are available.
44 * @param <E> The enum type subclass
47 * @see Class#getEnumConstants()
48 * @see java.util.EnumSet
49 * @see java.util.EnumMap
52 public abstract class Enum<E extends Enum<E>>
53 implements Comparable<E>, Serializable {
55 * The name of this enum constant, as declared in the enum declaration.
56 * Most programmers should use the {@link #toString} method rather than
57 * accessing this field.
59 private final String name;
62 * Returns the name of this enum constant, exactly as declared in its
65 * <b>Most programmers should use the {@link #toString} method in
66 * preference to this one, as the toString method may return
67 * a more user-friendly name.</b> This method is designed primarily for
68 * use in specialized situations where correctness depends on getting the
69 * exact name, which will not vary from release to release.
71 * @return the name of this enum constant
73 public final String name() {
78 * The ordinal of this enumeration constant (its position
79 * in the enum declaration, where the initial constant is assigned
80 * an ordinal of zero).
82 * Most programmers will have no use for this field. It is designed
83 * for use by sophisticated enum-based data structures, such as
84 * {@link java.util.EnumSet} and {@link java.util.EnumMap}.
86 private final int ordinal;
89 * Returns the ordinal of this enumeration constant (its position
90 * in its enum declaration, where the initial constant is assigned
91 * an ordinal of zero).
93 * Most programmers will have no use for this method. It is
94 * designed for use by sophisticated enum-based data structures, such
95 * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
97 * @return the ordinal of this enumeration constant
99 public final int ordinal() {
104 * Sole constructor. Programmers cannot invoke this constructor.
105 * It is for use by code emitted by the compiler in response to
106 * enum type declarations.
108 * @param name - The name of this enum constant, which is the identifier
109 * used to declare it.
110 * @param ordinal - The ordinal of this enumeration constant (its position
111 * in the enum declaration, where the initial constant is assigned
112 * an ordinal of zero).
114 protected Enum(String name, int ordinal) {
116 this.ordinal = ordinal;
120 * Returns the name of this enum constant, as contained in the
121 * declaration. This method may be overridden, though it typically
122 * isn't necessary or desirable. An enum type should override this
123 * method when a more "programmer-friendly" string form exists.
125 * @return the name of this enum constant
127 public String toString() {
132 * Returns true if the specified object is equal to this
135 * @param other the object to be compared for equality with this object.
136 * @return true if the specified object is equal to this
139 public final boolean equals(Object other) {
144 * Returns a hash code for this enum constant.
146 * @return a hash code for this enum constant.
148 public final int hashCode() {
149 return super.hashCode();
153 * Throws CloneNotSupportedException. This guarantees that enums
154 * are never cloned, which is necessary to preserve their "singleton"
157 * @return (never returns)
159 protected final Object clone() throws CloneNotSupportedException {
160 throw new CloneNotSupportedException();
164 * Compares this enum with the specified object for order. Returns a
165 * negative integer, zero, or a positive integer as this object is less
166 * than, equal to, or greater than the specified object.
168 * Enum constants are only comparable to other enum constants of the
169 * same enum type. The natural order implemented by this
170 * method is the order in which the constants are declared.
172 public final int compareTo(E o) {
173 Enum other = (Enum)o;
175 if (self.getClass() != other.getClass() && // optimization
176 self.getDeclaringClass() != other.getDeclaringClass())
177 throw new ClassCastException();
178 return self.ordinal - other.ordinal;
182 * Returns the Class object corresponding to this enum constant's
183 * enum type. Two enum constants e1 and e2 are of the
184 * same enum type if and only if
185 * e1.getDeclaringClass() == e2.getDeclaringClass().
186 * (The value returned by this method may differ from the one returned
187 * by the {@link Object#getClass} method for enum constants with
188 * constant-specific class bodies.)
190 * @return the Class object corresponding to this enum constant's
193 public final Class<E> getDeclaringClass() {
194 Class clazz = getClass();
195 Class zuper = clazz.getSuperclass();
196 return (zuper == Enum.class) ? clazz : zuper;
200 * Returns the enum constant of the specified enum type with the
201 * specified name. The name must match exactly an identifier used
202 * to declare an enum constant in this type. (Extraneous whitespace
203 * characters are not permitted.)
205 * <p>Note that for a particular enum type {@code T}, the
206 * implicitly declared {@code public static T valueOf(String)}
207 * method on that enum may be used instead of this method to map
208 * from a name to the corresponding enum constant. All the
209 * constants of an enum type can be obtained by calling the
210 * implicit {@code public static T[] values()} method of that
213 * @param <T> The enum type whose constant is to be returned
214 * @param enumType the {@code Class} object of the enum type from which
215 * to return a constant
216 * @param name the name of the constant to return
217 * @return the enum constant of the specified enum type with the
219 * @throws IllegalArgumentException if the specified enum type has
220 * no constant with the specified name, or the specified
221 * class object does not represent an enum type
222 * @throws NullPointerException if {@code enumType} or {@code name}
226 public static <T extends Enum<T>> T valueOf(Class<T> enumType,
228 throw new UnsupportedOperationException();
229 // T result = enumType.enumConstantDirectory().get(name);
230 // if (result != null)
233 // throw new NullPointerException("Name is null");
234 // throw new IllegalArgumentException(
235 // "No enum constant " + enumType.getCanonicalName() + "." + name);
239 * enum classes cannot have finalize methods.
241 protected final void finalize() { }
244 * prevent default deserialization
246 // private void readObject(ObjectInputStream in) throws IOException,
247 // ClassNotFoundException {
248 // throw new InvalidObjectException("can't deserialize enum");
251 // private void readObjectNoData() throws ObjectStreamException {
252 // throw new InvalidObjectException("can't deserialize enum");