JAVAJava中的lang.Enum类

Enum类在java中存在。朗包。它是所有Java语言枚举类型的公共基类。有关枚举的信息，请参阅 java中的枚举

类别声明

public abstract class Enum<E extends Enum>
extends Object
implements Comparable, Serializable

正如我们所见，枚举是一个 摘要 同学们，所以我们 不能 创建类Enum的对象。

枚举类中的方法

Enum类提供了10个有用的方法。它们中的大多数都是从 对象 班这些方法在Enum类中声明为final，因此程序员不能修改任何Enum常量。

1. 最终字符串名（） ：此方法返回此枚举常量的名称，该名称与其枚举声明中声明的名称完全相同。

   Syntax : 
   public final String name()
   Parameters : 
   NA
   Returns :
   the name of this enum constant
   

   // Java program to demonstrate name() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) { Color c1 = Color.RED; System.out.print( "Name of enum constant: " ); // name method System.out.println(c1.name()); } }

   输出：

   Name of enum constant: RED
   

2. 最终整数序数（） ：此方法返回此枚举常量的索引。

   Syntax : 
   public final int ordinal()
   Parameters : 
   NA
   Returns :
   the ordinal of this enumeration constant
   

   // Java program to demonstrate ordinal() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) { Color c1 = Color.GREEN; System.out.print( "ordinal of enum constant " +c1.name()+ " : " ); // ordinal method System.out.println(c1.ordinal()); } }

   输出：

   ordinal of enum constant GREEN : 1
   

3. String to字符串（） ：此方法返回表示此枚举常量的字符串对象。此方法与name（）方法相同。

   Syntax : 
   public String toString()
   Parameters : 
   NA
   Returns :
   a string representation of this enumeration constant
   Overrides :
   toString in class Object
   

   // Java program to demonstrate toString() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) { Color c1 = Color.GREEN; // getting string representation of enum // using toString() method String str = c1.toString(); System.out.println(str); } }

   输出：

   GREEN
   

4. 最终布尔等于（对象obj） ：如果指定的对象等于此枚举常量，则此方法返回true，否则返回false。

   Syntax : 
   public final boolean equals(Object obj)
   Parameters : 
   obj - the object too be compared for equality with this enum.
   Returns :
   true if the specified object is equal to this enum constant. 
   false otherwise
   Overrides :
   equals in class Object
   

   // Java program to demonstrate equals() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) { Color c1 = Color.RED; Color c2 = Color.GREEN; Color c3 = Color.RED; // checking equality between enums // using equals() method boolean b1 = c1.equals(c2); boolean b2 = c1.equals(c3); boolean b3 = c2.equals( null ); System.out.println( "is c1 equal to c2 : " + b1); System.out.println( "is c1 equal to c3 : " + b2); System.out.println( "is c2 equal to null : " + b3); } }

   输出：

   is c1 equal to c2 : false
   is c1 equal to c3 : true
   is c2 equal to null : false
   

5. final int hashCode（） ：此方法返回此枚举常量的哈希代码。实际上，这个方法只包含一条语句，即“return super.hashCode（）”，它反过来调用对象类hashCode（）方法。

   Syntax : 
   public final int hashCode()
   Parameters : 
   NA
   Returns :
   a hash code for this enum constant.
   Overrides :
   hashCode in class Object
   

   // Java program to demonstrate hashCode() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) { Color c1 = Color.RED; System.out.print( "hashcode of enum constant " + c1.name() + " : " ); // hashcode method System.out.println(c1.hashCode()); Color c2 = Color.GREEN; System.out.print( "hashcode of enum constant " + c2.name() + " : " ); // hashcode method System.out.println(c2.hashCode()); } }

   输出：

   hashcode of enum constant RED : 366712642
   hashcode of enum constant GREEN : 1829164700
   

6. 最终国际比较（E obj） ：此方法将此枚举与指定的对象进行“比较” 顺序 .枚举常量只能与同一枚举类型的其他枚举常量进行比较。

   Syntax : 
   public int compareTo(E obj)
   Parameters : 
   obj - the object to be compared.
   Returns :
   a negative integer if this object is at less ordinal than the specified object
   zero if this object is at equal ordinal than the specified object
   a positive integer if this object is at greater ordinal than the specified object
   Throws :
   NullPointerException - if the argument is null
   

   // Java program to demonstrate compareTo() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) { Color c1 = Color.RED; Color c2 = Color.GREEN; Color c3 = Color.RED; Color c4 = Color.BLUE; System.out.print( "Comparing " +c1.name()+ " with " + c2.name() + " : " ); // compareTo method System.out.println(c1.compareTo(c2)); System.out.print( "Comparing " +c1.name()+ " with " + c3.name() + " : " ); // compareTo method System.out.println(c1.compareTo(c3)); System.out.print( "Comparing " +c4.name()+ " with " + c2.name() + " : " ); // compareTo method System.out.println(c4.compareTo(c2)); // The following statement throw NullPointerException // as argument of compareTo method is null // System.out.println(c4.compareTo(null)); } }

   输出：

   Comparing RED with GREEN : -1
   Comparing RED with RED : 0
   Comparing BLUE with GREEN : 1
   

7. static T valueOf（类枚举类型，字符串名称） ：此方法返回具有指定名称的指定枚举类型的枚举常量。该名称必须与用于在此类型中声明枚举常量的标识符完全匹配。

   Syntax : 
   public static <T extends Enum> T valueOf(Class enumType,String name)
   TypeParameters : 
   T - The enum type whose constant is to be returned
   Parameters : 
   enumType - the Class object of the enum type from which to return a constant
   name - the name of the constant to return
   Returns :
   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
   NullPointerException - if enumType or name is null
   

   // Java program to demonstrate valueOf() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) { // getting value of enum with specified String // using valueOf method Color c1 = Color.valueOf( "RED" ); Color c2 = Color.valueOf( "GREEN" ); // name method System.out.println(c1.name()); System.out.println(c2.name()); // The following statement throw IllegalArgumentException // as GrEEN is not an enum constant //  Color c3 = Color.valueOf("GrEEN"); // The following statement throw NullPointerException // as argument of valueOf method is null // Color c4 = Color.valueOf(null); } }

   输出：

   RED
   GREEN
   

8. 最终类 getDeclaringClass（） ：此方法返回与此枚举常量的枚举类型对应的类对象。如果此方法为两个枚举常量e1和e2返回相同的类对象，则任意两个枚举常量e1和e2都属于相同的枚举类型。

   Syntax : 
   public final Class <E> getDeclaringClass()
   Parameters : 
   NA
   Returns :
   the Class object corresponding to this enum constant's enum type
   

   // Java program to demonstrate getDeclaringClass() method enum Color { RED, GREEN, BLUE; } enum Day { MONDAY, TUESDAY ; } public class Test { // Driver method public static void main(String[] args) { // getting value of enum with specified String // using valueOf method Color c1 = Color.valueOf( "RED" ); Color c2 = Color.valueOf( "GREEN" ); Day d1 = Day.valueOf( "MONDAY" ); Day d2 = Day.valueOf( "TUESDAY" ); System.out.print( "Class corresponding to " + c1.name() + " : " ); // getDeclaringClass method System.out.println(c1.getDeclaringClass()); System.out.print( "Class corresponding to " + c2.name() + " : " ); // getDeclaringClass method System.out.println(c2.getDeclaringClass()); System.out.print( "Class corresponding to " + d1.name() + " : " ); // getDeclaringClass method System.out.println(d1.getDeclaringClass()); System.out.print( "Class corresponding to " + d2.name() + " : " ); // getDeclaringClass method System.out.println(d2.getDeclaringClass()); } }

   输出：

   Class corresponding to RED : class Color
   Class corresponding to GREEN : class Color
   Class corresponding to MONDAY : class Day
   Class corresponding to TUESDAY : class Day
   

9. 最终对象克隆（） ：此方法保证从不克隆枚举，这是保持其“单例”状态所必需的。编译器在内部使用它来创建枚举常量。

   Syntax : 
   public final Object clone() throws CloneNotSupportedException
   Parameters : 
   NA
   Returns :
   NA
   Overrides :
   clone in class Object
   Throws :
   CloneNotSupportedException-if the object's class does not support the Cloneable interface.
   

   // Java program to demonstrate clone() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) throws CloneNotSupportedException { System.out.println( "Enums are never cloned" ); Test t = new Test() { // final clone method protected final Object clone() throws CloneNotSupportedException { return new CloneNotSupportedException(); } }; System.out.println(t.clone()); } }

   输出：

   Enums are never cloned
   java.lang.CloneNotSupportedException
   

10. 最终作废定稿（） ：此方法保证枚举类不能有finalize方法。

    Syntax : 
    protected final void finalize()
    Parameters : 
    NA
    Returns :
    NA
    Overrides :
    finalize in class Object
    

    // Java program to demonstrate finalize() method enum Color { RED, GREEN, BLUE; } public class Test { // Driver method public static void main(String[] args) throws Throwable { System.out.println( "enum classes cannot have finalize methods" ); Test t = new Test() { // final finalize method protected final void finalize() throws Throwable { // empty implementation }; }; } }

    输出：

    enum classes cannot have finalize methods
    

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