是Java中的枚举类型

Question

I finally have a reason to implement an enum in Java and and find it to be an invalid type in 1.6. So I declare the enum as

public enum MyEnum = {A=0, B=1, C=3}; 

and get an error invalid type in Eclipse.

Answer 1

That's not how they are used. See examples at http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html , such as

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
    THURSDAY, FRIDAY, SATURDAY 
}

Java enums are much more powerful than in, say, C#. They're (almost) full-blown objects, and thus cannot be represented with just a number. They can however contain a number, and they do have an ordinal number value .

You could have the number value with

public enum MyEnum {
    A(0), B(1), C(3);

    private final int number;
    MyEnum(int number) {
      this.number = number;
    }
}

Answer 2

Java enums are quite different to C and C++ enums . The biggest difference is that the enum constants are full-blown objects rather than compile-time integer constants.

In your example, A , B and C are objects. Therefore constructs like A=0, B=1, C=3 are not allowed.

I recommend taking a look at the tutorial .

If you have to associate numeric values with enum constants, you can achieve a similar effect like so:

public enum MyEnum {
    A(0), B(1), C(3);
    public final int val;
    private MyEnum(int val) {
        this.val = val;
    }
}

Having done this, you can access the values using MyEnum.A.val etc.

Answer 3

In Java, enum is a type, but it is incompatible with integers. Enum objects are closer to classes than to primitives, in that they can have methods, member variables, and so on.

Java lets you get the effect that you wanted by adding an int member to your enumeration, and initializing it differently for different enumeration members, like this:

public enum MyEnum {
    A(1), B(2), C(3);
    int val;
    private MyEnum (int v) {
        val = v;
    }
    public int value() {
        return val;
    }
};

Now each member of your enum has a public method value() that returns the integer value associated with the corresponding element of the enumeration.

Answer 4

you can't do this as you do. enum define in java in the following way

enum myenum{a,b,c,d}

Answer 5

public enum ModuleType {A,B,C}

Answer 6

To answer your question: enum is technically not a type. Therefore you cannot define a variable of type enum as you have tried.

enum is a keyword to define an enumerated (abbreviated to enum) type which is a special data type. Once an enum type is defined (very much like how you would define a class), you refer to it using the name of the enum type. Please check the enum types documentation .