创建Java枚举的替代方法？

Question

I have the following code that I am trying to understand:

public class A {    
    enum Size {S, M, L };  
    Size size = Size.M; 
} 

I understand the first enum line is creating an enum with three values but what is the second line doing? What will the variable size hold and is this another way to construct an enum?

Answer 1

The second line is just giving to the field size (of type Size ) of the instance of class A the initial value Size.M .

You may be a little disturbed here by the fact that the enum is created inside the class A , it could have been in another file (but it's perfectly OK to put it inside the class A if it's used only there).

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EDIT (not really part of the answer) : here's a (not pretty) exemple of enum declaration so that you can better understand the form of an enum declaration :

public enum QueryError {

    no_request("no_request", "No request in client call"),
    no_alias_requested("no_alias_requested", "no alias requested"),
    session_not_found("session_not_found", "wrong session id"),
    synosteelQuery_not_found("sxxx_not_found", "sxxx not found");

    public JsonpServerResponse.Error error;

    private QueryError(String type, String details) {
        this.error = new JsonpServerResponse.Error();
        this.error.type = type;
        this.error.detail = details;
    }
}

Answer 2

第二个类似的方法是在类A声明一个类型为Size的包私有成员变量，并将其初始化以指向Size.M

Answer 3

An enum is a type (just as a class is a type). The second line is creating an instance variable called size, which has a type of Size (since an enum is a type). Then it's initializing the value of that instance variable to an instance of the enum Size (specifically, the Size.M instance).