java.lang.inc,src/java/lang/Enum.java · 乔一/LearningJDK - Gitee.com
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
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* 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.
*
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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;
/**
* 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
* The Java™ Language Specification.
*
*
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 The enum type subclass
*
* @author Josh Bloch
* @author Neal Gafter
* @see Class#getEnumConstants()
* @see java.util.EnumSet
* @see java.util.EnumMap
* @since 1.5
*/
/*
* 可以看作是所有enum的包装类，不过Enum类是禁止直接继承的
*
* 示例：
* public enum Color {
* WHITE, BLACK
* }
*
* 等价于：
* public final class Color extends Enum {
* public static final Color WHITE = new Color("WHITE", 0);
* public static final Color BLACK = new Color("BLACK", 1);
*
* public Color(String name, int ordinal) {
* super(name, ordinal);
* }
*
* // ......
* }
*/
@SuppressWarnings("serial")
public abstract class Enum> implements Comparable, Serializable {
/* No serialVersionUID needed due to special-casing of enum types. */
/**
* 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; // 枚举实例名称
/**
* 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; // 枚举实例的值
/**
* 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, exactly as declared in its
* enum declaration.
*
* Most programmers should use the {@link #toString} method in
* preference to this one, as the toString method may return
* a more user-friendly name. 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
*/
// 返回枚举实例名称
public final String name() {
return name;
}
/**
* 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
*/
// 返回枚举实例的值
public final int ordinal() {
return 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
*/
// 返回枚举类类对象
@SuppressWarnings("unchecked")
public final Class getDeclaringClass() {
Class> clazz = getClass();
Class> zuper = clazz.getSuperclass();
return (zuper == Enum.class) ? (Class) clazz : (Class) zuper;
}
/**
* 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.
*/
// 比较枚举实例的值；声明靠前的枚举，其"值"较小
public final int compareTo(E o) {
Enum> other = (Enum>) o;
Enum self = this;
if(self.getClass() != other.getClass() && // optimization
self.getDeclaringClass() != other.getDeclaringClass()) {
throw new ClassCastException();
}
return self.ordinal - other.ordinal;
}
/**
* 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.)
*
*
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 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
*/
/*
* 获取枚举类enumType中名称为name的枚举实例，其他实例不受影响
* Color c = Enum.valueOf(Color.class, "WHITE");
*/
public static > T valueOf(Class 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);
}
/*▼ 继承自Object ████████████████████████████████████████████████████████████████████████████████┓ */
/**
* Returns a hash code for this enum constant.
*
* @return a hash code for this enum constant.
*/
public final int hashCode() {
return super.hashCode();
}
/**
* 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 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;
}
/**
* 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();
}
/**
* enum classes cannot have finalize methods.
*/
@SuppressWarnings("deprecation")
protected final void finalize() {
}
/*▲ 继承自Object ████████████████████████████████████████████████████████████████████████████████┛ */
/**
* prevent default deserialization
*/
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
throw new InvalidObjectException("can't deserialize enum");
}
private void readObjectNoData() throws ObjectStreamException {
throw new InvalidObjectException("can't deserialize enum");
}
}
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