/*

 * Copyright (c) 2003, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package java.lang;

import java.io.IOException;

import java.io.InvalidObjectException;

import java.io.ObjectInputStream;

import java.io.ObjectStreamException;

import java.io.Serializable;

import java.lang.constant.ClassDesc;

import java.lang.constant.Constable;

import java.lang.constant.ConstantDescs;

import java.lang.constant.DynamicConstantDesc;

import java.lang.invoke.MethodHandles;

import java.util.Optional;

import static java.util.Objects.requireNonNull;

/**

 * This is the common base class of all Java language enumeration types.

 *

 * More information about enums, including descriptions of the

 * implicitly declared methods synthesized by the compiler, can be

 * found in section 8.9 of

 * <cite>The Java&trade; Language Specification</cite>.

 *

 * <p> Note that when using an enumeration type as the type of a set

 * or as the type of the keys in a map, specialized and efficient

 * {@linkplain java.util.EnumSet set} and {@linkplain

 * java.util.EnumMap map} implementations are available.

 *

 * @param <E> The enum type subclass

 * @serial exclude

 * @author  Josh Bloch

 * @author  Neal Gafter

 * @see     Class#getEnumConstants()

 * @see     java.util.EnumSet

 * @see     java.util.EnumMap

 * @jls 8.9 Enum Types

 * @jls 8.9.3 Enum Members

 * @since   1.5

 */

@SuppressWarnings("serial") // No serialVersionUID needed due to

                            // special-casing of enum types.

public abstract class Enum<E extends Enum<E>>

        implements Constable, Comparable<E>, Serializable {

    /**

     * The name of this enum constant, as declared in the enum declaration.

     * Most programmers should use the {@link #toString} method rather than

     * accessing this field.

     */

    private final String name;

    /**

     * Returns the name of this enum constant, exactly as declared in its

     * enum declaration.

     *

     * <b>Most programmers should use the {@link #toString} method in

     * preference to this one, as the toString method may return

     * a more user-friendly name.</b>  This method is designed primarily for

     * use in specialized situations where correctness depends on getting the

     * exact name, which will not vary from release to release.

     *

     * @return the name of this enum constant

     */

    public final String name() {

        return name;

    }

    /**

     * The ordinal of this enumeration constant (its position

     * in the enum declaration, where the initial constant is assigned

     * an ordinal of zero).

     *

     * Most programmers will have no use for this field.  It is designed

     * for use by sophisticated enum-based data structures, such as

     * {@link java.util.EnumSet} and {@link java.util.EnumMap}.

     */

    private final int ordinal;

    /**

     * Returns the ordinal of this enumeration constant (its position

     * in its enum declaration, where the initial constant is assigned

     * an ordinal of zero).

     *

     * Most programmers will have no use for this method.  It is

     * designed for use by sophisticated enum-based data structures, such

     * as {@link java.util.EnumSet} and {@link java.util.EnumMap}.

     *

     * @return the ordinal of this enumeration constant

     */

    public final int ordinal() {

        return ordinal;

    }

    /**

     * Sole constructor.  Programmers cannot invoke this constructor.

     * It is for use by code emitted by the compiler in response to

     * enum type declarations.

     *

     * @param name - The name of this enum constant, which is the identifier

     *               used to declare it.

     * @param ordinal - The ordinal of this enumeration constant (its position

     *         in the enum declaration, where the initial constant is assigned

     *         an ordinal of zero).

     */

    protected Enum(String name, int ordinal) {

        this.name = name;

        this.ordinal = ordinal;

    }

    /**

     * Returns the name of this enum constant, as contained in the

     * declaration.  This method may be overridden, though it typically

     * isn't necessary or desirable.  An enum type should override this

     * method when a more "programmer-friendly" string form exists.

     *

     * @return the name of this enum constant

     */

    public String toString() {

        return name;

    }

    /**

     * Returns true if the specified object is equal to this

     * enum constant.

     *

     * @param other the object to be compared for equality with this object.

     * @return  true if the specified object is equal to this

     *          enum constant.

     */

    public final boolean equals(Object other) {

        return this==other;

    }

    /**

     * Returns a hash code for this enum constant.

     *

     * @return a hash code for this enum constant.

     */

    public final int hashCode() {

        return super.hashCode();

    }

    /**

     * Throws CloneNotSupportedException.  This guarantees that enums

     * are never cloned, which is necessary to preserve their "singleton"

     * status.

     *

     * @return (never returns)

     */

    protected final Object clone() throws CloneNotSupportedException {

        throw new CloneNotSupportedException();

    }

    /**

     * Compares this enum with the specified object for order.  Returns a

     * negative integer, zero, or a positive integer as this object is less

     * than, equal to, or greater than the specified object.

     *

     * Enum constants are only comparable to other enum constants of the

     * same enum type.  The natural order implemented by this

     * method is the order in which the constants are declared.

     */

    public final int compareTo(E o) {

        Enum<?> other = (Enum<?>)o;

        Enum<E> self = this;

        if (self.getClass() != other.getClass() && // optimization

            self.getDeclaringClass() != other.getDeclaringClass())

            throw new ClassCastException();

        return self.ordinal - other.ordinal;

    }

    /**

     * Returns the Class object corresponding to this enum constant's

     * enum type.  Two enum constants e1 and  e2 are of the

     * same enum type if and only if

     *   e1.getDeclaringClass() == e2.getDeclaringClass().

     * (The value returned by this method may differ from the one returned

     * by the {@link Object#getClass} method for enum constants with

     * constant-specific class bodies.)

     *

     * @return the Class object corresponding to this enum constant's

     *     enum type

     */

    @SuppressWarnings("unchecked")

    public final Class<E> getDeclaringClass() {

        Class<?> clazz = getClass();

        Class<?> zuper = clazz.getSuperclass();

        return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;

    }

    /**

     * Returns an enum descriptor {@code EnumDesc} for this instance, if one can be

     * constructed, or an empty {@link Optional} if one cannot be.

     *

     * @return An {@link Optional} containing the resulting nominal descriptor,

     * or an empty {@link Optional} if one cannot be constructed.

     * @since 12

     */

    @Override

    public final Optional<EnumDesc<E>> describeConstable() {

        return getDeclaringClass()

                .describeConstable()

                .map(c -> EnumDesc.of(c, name));

    }

    /**

     * Returns the enum constant of the specified enum type with the

     * specified name.  The name must match exactly an identifier used

     * to declare an enum constant in this type.  (Extraneous whitespace

     * characters are not permitted.)

     *

     * <p>Note that for a particular enum type {@code T}, the

     * implicitly declared {@code public static T valueOf(String)}

     * method on that enum may be used instead of this method to map

     * from a name to the corresponding enum constant.  All the

     * constants of an enum type can be obtained by calling the

     * implicit {@code public static T[] values()} method of that

     * type.

     *

     * @param <T> The enum type whose constant is to be returned

     * @param enumType the {@code Class} object of the enum type from which

     *      to return a constant

     * @param name the name of the constant to return

     * @return the enum constant of the specified enum type with the

     *      specified name

     * @throws IllegalArgumentException if the specified enum type has

     *         no constant with the specified name, or the specified

     *         class object does not represent an enum type

     * @throws NullPointerException if {@code enumType} or {@code name}

     *         is null

     * @since 1.5

     */

    public static <T extends Enum<T>> T valueOf(Class<T> enumType,

                                                String name) {

        T result = enumType.enumConstantDirectory().get(name);

        if (result != null)

            return result;

        if (name == null)

            throw new NullPointerException("Name is null");

        throw new IllegalArgumentException(

            "No enum constant " + enumType.getCanonicalName() + "." + name);

    }

    /**

     * enum classes cannot have finalize methods.

     */

    @SuppressWarnings("deprecation")

    protected final void finalize() { }

    /**

     * prevent default deserialization

     */

    @java.io.Serial

    private void readObject(ObjectInputStream in) throws IOException,

        ClassNotFoundException {

        throw new InvalidObjectException("can't deserialize enum");

    }

    @java.io.Serial

    private void readObjectNoData() throws ObjectStreamException {

        throw new InvalidObjectException("can't deserialize enum");

    }

    /**

     * A <a href="{@docRoot}/java.base/java/lang/constant/package-summary.html#nominal">nominal descriptor</a> for an

     * {@code enum} constant.

     *

     * @param <E> the type of the enum constant

     *

     * @since 12

     */

    public static final class EnumDesc<E extends Enum<E>>

            extends DynamicConstantDesc<E> {

        /**

         * Constructs a nominal descriptor for the specified {@code enum} class and name.

         *

         * @param constantType a {@link ClassDesc} describing the {@code enum} class

         * @param constantName the unqualified name of the enum constant

         * @throws NullPointerException if any argument is null

         * @jvms 4.2.2 Unqualified Names

         */

        private EnumDesc(ClassDesc constantType, String constantName) {

            super(ConstantDescs.BSM_ENUM_CONSTANT, requireNonNull(constantName), requireNonNull(constantType));

        }

        /**

         * Returns a nominal descriptor for the specified {@code enum} class and name

         *

         * @param <E> the type of the enum constant

         * @param enumClass a {@link ClassDesc} describing the {@code enum} class

         * @param constantName the unqualified name of the enum constant

         * @return the nominal descriptor

         * @throws NullPointerException if any argument is null

         * @jvms 4.2.2 Unqualified Names

         * @since 12

         */

        public static<E extends Enum<E>> EnumDesc<E> of(ClassDesc enumClass,

                                                        String constantName) {

            return new EnumDesc<>(enumClass, constantName);

        }

        @Override

        @SuppressWarnings("unchecked")

        public E resolveConstantDesc(MethodHandles.Lookup lookup)

                throws ReflectiveOperationException {

            return Enum.valueOf((Class<E>) constantType().resolveConstantDesc(lookup), constantName());

        }

        @Override

        public String toString() {

            return String.format("EnumDesc[%s.%s]", constantType().displayName(), constantName());

        }

    }

}