Module java.base
Package java.lang

Class Enum<E extends Enum<E>>

java.lang.Object
java.lang.Enum<E>
Type Parameters:
E - The type of the enum subclass
All Implemented Interfaces:
Serializable, Comparable<E>, Constable

public abstract class Enum<E extends Enum<E>> extends Object implements Constable, Comparable<E>, Serializable
This is the common base class of all Java language enumeration classes. 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. Enumeration classes are all serializable and receive special handling by the serialization mechanism. The serialized representation used for enum constants cannot be customized. Declarations of methods and fields that would otherwise interact with serialization are ignored, including serialVersionUID; see the Java Object Serialization Specification for details.

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 set and map implementations are available.

See Java Language Specification:
8.9 Enum Classes
8.9.3 Enum Members
Since:
1.5
See Also:
Class.getEnumConstants(), EnumSet, EnumMap
  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static final class 
    Enum.EnumDesc<E extends Enum<E>>
    A nominal descriptor for an enum constant.
  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    Enum​(String name, int ordinal)
    Sole constructor.
  • Method Summary

    Modifier and Type
    Method
    Description
    protected final Object
    Throws CloneNotSupportedException.
    final int
    compareTo​(E o)
    Compares this enum with the specified object for order.
    Returns an enum descriptor EnumDesc for this instance, if one can be constructed, or an empty Optional if one cannot be.
    final boolean
    equals​(Object other)
    Returns true if the specified object is equal to this enum constant.
    protected final void
    enum classes cannot have finalize methods.
    final Class<E>
    Returns the Class object corresponding to this enum constant's enum type.
    final int
    Returns a hash code for this enum constant.
    final String
    Returns the name of this enum constant, exactly as declared in its enum declaration.
    final int
    Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero).
    Returns the name of this enum constant, as contained in the declaration.
    static <T extends Enum<T>>
    T
    valueOf​(Class<T> enumClass, String name)
    Returns the enum constant of the specified enum class with the specified name.

    Methods declared in class java.lang.Object

    getClass, notify, notifyAll, wait, wait, wait
  • Constructor Details

    • Enum

      protected Enum(String name, int ordinal)
      Sole constructor. Programmers cannot invoke this constructor. It is for use by code emitted by the compiler in response to enum class declarations.
      Parameters:
      name - - The name of this enum constant, which is the identifier used to declare it.
      ordinal - - The ordinal of this enumeration constant (its position in the enum declaration, where the initial constant is assigned an ordinal of zero).
  • Method Details

    • name

      public final String name()
      Returns the name of this enum constant, exactly as declared in its enum declaration. Most programmers should use the 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.
      Returns:
      the name of this enum constant
    • ordinal

      public 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 EnumSet and EnumMap.
      Returns:
      the ordinal of this enumeration constant
    • toString

      public String toString()
      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 class should override this method when a more "programmer-friendly" string form exists.
      Overrides:
      toString in class Object
      Returns:
      the name of this enum constant
    • equals

      public final boolean equals(Object other)
      Returns true if the specified object is equal to this enum constant.
      Overrides:
      equals in class Object
      Parameters:
      other - the object to be compared for equality with this object.
      Returns:
      true if the specified object is equal to this enum constant.
      See Also:
      Object.hashCode(), HashMap
    • hashCode

      public final int hashCode()
      Returns a hash code for this enum constant.
      Overrides:
      hashCode in class Object
      Returns:
      a hash code for this enum constant.
      See Also:
      Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)
    • clone

      protected final Object clone() throws CloneNotSupportedException
      Throws CloneNotSupportedException. This guarantees that enums are never cloned, which is necessary to preserve their "singleton" status.
      Overrides:
      clone in class Object
      Returns:
      (never returns)
      Throws:
      CloneNotSupportedException - if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.
      See Also:
      Cloneable
    • compareTo

      public final int compareTo(E o)
      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.
      Specified by:
      compareTo in interface Comparable<E extends Enum<E>>
      Parameters:
      o - the object to be compared.
      Returns:
      a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.
    • getDeclaringClass

      public final Class<E> getDeclaringClass()
      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 Object.getClass() method for enum constants with constant-specific class bodies.)
      Returns:
      the Class object corresponding to this enum constant's enum type
    • describeConstable

      public final Optional<Enum.EnumDesc<E>> describeConstable()
      Returns an enum descriptor EnumDesc for this instance, if one can be constructed, or an empty Optional if one cannot be.
      Specified by:
      describeConstable in interface Constable
      Returns:
      An Optional containing the resulting nominal descriptor, or an empty Optional if one cannot be constructed.
      Since:
      12
    • valueOf

      public static <T extends Enum<T>> T valueOf(Class<T> enumClass, String name)
      Returns the enum constant of the specified enum class with the specified name. The name must match exactly an identifier used to declare an enum constant in this class. (Extraneous whitespace characters are not permitted.)

      Note that for a particular enum class T, the implicitly declared 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 class can be obtained by calling the implicit public static T[] values() method of that class.

      Type Parameters:
      T - The enum class whose constant is to be returned
      Parameters:
      enumClass - the Class object of the enum class from which to return a constant
      name - the name of the constant to return
      Returns:
      the enum constant of the specified enum class with the specified name
      Throws:
      IllegalArgumentException - if the specified enum class has no constant with the specified name, or the specified class object does not represent an enum class
      NullPointerException - if enumClass or name is null
      Since:
      1.5
    • finalize

      protected final void finalize()
      enum classes cannot have finalize methods.
      Overrides:
      finalize in class Object
      See Also:
      WeakReference, PhantomReference