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Java Java.lang.Enum用法及代码示例


枚举类存在于 java.lang 包中。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enum in java

Class Declaration 

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

正如我们所看到的，Enum 是一个Abstract类，所以我们不能创建 Enum 类的对象。

Methods in Enum Class

Enum 类提供了 10 个有用的方法。其中大多数是从 Object 类覆盖的。这些方法在 Enum 类中声明为 Final，因此程序员无法修改任何枚举常量。

  1. 最终字符串name()：此方法返回此枚举常量的名称，该名称与其枚举声明中的声明完全相同。
    Syntax : 
public final String name()
Parameters : 
NA
返回：
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int ordinal()：该方法返回该枚举常量的索引。
    Syntax : 
public final int ordinal()
Parameters : 
NA
返回：
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. 字符串toString()：此方法返回表示此枚举常量的 String 对象。此方法与name()方法相同。
    Syntax : 
public String toString()
Parameters : 
NA
返回：
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. 最终布尔值 equals(Object 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.
返回：
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. 最终int hashCode()：此方法返回此枚举常量的哈希码。实际上这个方法只包含一条语句，即“return super.hashCode()”，该语句又调用了Object类的hashCode()方法。
    Syntax : 
public final int hashCode()
Parameters : 
NA
返回：
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intcompareTo(E obj)：这个方法“compares”这个枚举与指定对象为次序。枚举常量只能与相同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.
返回：
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 extends Enum> T valueOf(类枚举类型，字符串名称)：该方法返回具有指定名称的指定枚举类型的枚举常量。该名称必须与用于声明此类型的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
返回：
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<E>getDeclaringClass()：该方法返回与该枚举常量的枚举类型对应的 Class 对象。任意 如果此方法返回相同的 Class 对象，则两个枚举常量 e1 和 e2 具有相同的枚举类型。
    Syntax : 
public final Class <E> getDeclaringClass()
Parameters : 
NA
返回：
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clone()：此方法保证枚举永远不会被克隆，这是保留其 “singleton” 状态所必需的。编译器在内部使用它来创建 Enum 常量。
    Syntax : 
public final Object clone() throws CloneNotSupportedException
Parameters : 
NA
返回：
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. 最终无效finalize()：该方法保证枚举类不能有finalize方法。
    Syntax : 
protected final void finalize()
Parameters : 
NA
返回：
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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注：本文由纯净天空筛选整理自佚名大神的英文原创作品 Java.lang.Enum Class in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。