Java-枚举和构造函数中的函数/变量存在问题

Question

I have been trying to understand what is going on in this piece of Java code, but so far I didn't manage. This is part of this library .

My wonders are on

CURRENT_SIM_TIME(Constants.VAR_TIME_STEP), NET_BOUNDARIES(Constants.VAR_NET_BOUNDING_BOX)

They do not appear previously in the code and later on, there is one constructor which uses CURRENT_SIM_TIME without any brackets () .

enum Variable {
        CURRENT_SIM_TIME(Constants.VAR_TIME_STEP), NET_BOUNDARIES(
                Constants.VAR_NET_BOUNDING_BOX), ;
        public final int id;
        private Variable(int id) {
            this.id = id;
        }
}

This the constructor I was talking about:

SimulationData(DataInputStream dis, DataOutputStream dos) {
        super("", Variable.class);
        addReadQuery(Variable.CURRENT_SIM_TIME,
                new ReadObjectVarQuery.IntegerQ(dis, dos,
                        Constants.CMD_GET_SIM_VARIABLE, "",
                        Variable.CURRENT_SIM_TIME.id) {

                });

        addReadQuery(Variable.NET_BOUNDARIES,
                new ReadObjectVarQuery.BoundingBoxQ(dis, dos,
                        Constants.CMD_GET_SIM_VARIABLE, "",
                        Variable.NET_BOUNDARIES.id));

        this.dis = dis;
        this.dos = dos;

    }

So, how is this possible?

Inside the enum Variable we have CURRENT_SIM_TIME and NET_BOUNDARIES with an argument inside the brackets and then in the constructor we create an addReadQuery with Variable.CURRENT_SIM_TIME as well as Variable.NET_BOUNDARIES , without brackets as an argument.

Are these functions? Static variables? Are they be defined in some other part of the code and I am not able to find them?

I am really lost right now...

Answer 1

Declaring Enum :

enum Variable {
        CURRENT_SIM_TIME(Constants.VAR_TIME_STEP), NET_BOUNDARIES(
                Constants.VAR_NET_BOUNDING_BOX), ;
        public final int id;
        private Variable(int id) {
            this.id = id;
        }
}

So when you say CURRENT_SIM_TIME(Constants.VAR_TIME_STEP) inside your enum declaration, you are calling the constructor Variable(int id) such that for enum CURRENT_SIM_TIME the value of the id variable will be set to Constants.VAR_TIME_STEP for that enum itself.

Similar is the case for NET_BOUNDARIES

So if you want to get the value of id for CURRENT_SIM_TIME , you would do it like :

Variable.NET_BOUNDARIES.id

Using Enum

And when you use enum, you don't have to call it with constructor, because that's already done when you declare your enum. So you just use the enum.