Java enum java version

Java enum java version

* Информация для продвинутых юзеров. На самом деле возможно ограниченное наследование от Enum. Подробнее здесь: https://kibungo.livejournal.com/19999.html Пример наследования и переопределения общего метода:

 public enum MyEnum < VAL1 < public int returnMyVal()< return 20; >>, VAL2; public int returnMyVal() < return 10; >> ------------------------ System.out.println(MyEnum.VAL1.returnMyVal()) // 20 System.out.println(MyEnum.VAL2.returnMyVal()) // 10 

«По сравнению с обычными классами, на Enum наложили одно серьезное ограничение — от него невозможно наследоваться.» Что за бред вы пишете?! Все перечисления изначально неявно расширяют класс java.lang.Enum, а поскольку в Java нету множественного наследования, то и расширять enum уже больше ничего не может.

В статье enum в коде с маленькой буквы, в комментариях к коду — Enum с большой Почему не говорится, что это разные вещи? Если у нас несколько enum`ов с перечислениями в приложении и нам нужно передать один из них как аргумент в метод можно сделать просто так someMethod(Enum e) < и здесь написать условие для выбора одного из enum`ов >Т.е. не нужно приводить все enum`ы к единому интерфейсу или абстрактному классу, чтобы выбрать один из enum`ов Как я понял Enum(тот который с большой буквы) — это что-то типа пустого интерфейса для всех enum`ов

 @Override public String toString() < return "DayOfWeek'; 

В коде приведенного примера про школьника есть ошибка: задано поле private ScholarSchedule schedule, но сеттер для него не прописан, а так как оно изначально не инициализировано, получаете NullPointerException. Добавьте сеттер (либо просто сделайте это поле public, что есть костыль) для задания значения:

 public void setSchedule(ScholarSchedule schedule)

Ну или, в конце концов, поместите метод main в класс Scholar (видимо так и задумывалось автором примера изначально), тогда он будет иметь доступ к private ScholarSchedule schedule и сможет инициализировать его надлежащим образом.

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Java enum java version

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 set and map implementations are available.

Constructor Summary

Method Summary

Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero).

Methods declared in class java.lang.Object

Constructor Detail

Enum

Sole constructor. Programmers cannot invoke this constructor. It is for use by code emitted by the compiler in response to enum type declarations.

Method Detail

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.

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 .

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 type should override this method when a more "programmer-friendly" string form exists.

equals

hashCode

public final int hashCode()

clone

protected final Object clone() throws CloneNotSupportedException

Throws CloneNotSupportedException. This guarantees that enums are never cloned, which is necessary to preserve their "singleton" status.

compareTo

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.

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.)

valueOf

public static Enum> T valueOf​(Class enumType, String 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.) Note that for a particular enum type 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 type can be obtained by calling the implicit public static T[] values() method of that type.

finalize

protected final void finalize()

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Java enum java version

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 set and map implementations are available.

Constructor Summary

Method Summary

Returns the ordinal of this enumeration constant (its position in its enum declaration, where the initial constant is assigned an ordinal of zero).

Methods inherited from class java.lang.Object

Constructor Detail

Enum

Sole constructor. Programmers cannot invoke this constructor. It is for use by code emitted by the compiler in response to enum type declarations.

Method Detail

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.

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 .

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 type should override this method when a more "programmer-friendly" string form exists.

equals

hashCode

public final int hashCode()

clone

protected final Object clone() throws CloneNotSupportedException

Throws CloneNotSupportedException. This guarantees that enums are never cloned, which is necessary to preserve their "singleton" status.

compareTo

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.

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.)

valueOf

public static Enum> T valueOf(Class enumType, String 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.) Note that for a particular enum type 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 type can be obtained by calling the implicit public static T[] values() method of that type.

finalize

protected final void finalize()

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