Qfyilyi

This became my concern mainly because of this:

public enum Method {

    POST(new Host().getAssets()),

    GET("GET"),

    DELETE("DELETE"),

    PUT("PUT");



    private String method;



    Method(String s) {

        method = s;

    }



    private String getMethod() {

        return method;

    }

}

The Host class is Spring @ConfigurationProperties annotated to be injected with values from an application.properties file at runtime. If I write that as a value of an enum, will it create a new object instance of Host every time I use Method.POST?

No, It will create instance only once. This can be checked with a print statement like below. Here getAssets() and constructor has been called only once:

    public class Host {



    public static void main(String args) {

        System.out.println("Hello World!");

        System.out.println(Method.POST);

        System.out.println(Method.POST);

        System.out.println(Method.POST);

    }



    Host()

    {

        System.out.println("--------------");

    }



    String getAssets()

    {

        System.out.println("ssssssssssss");

        return "eeee";

    }

}





enum Method {

    POST(new Host().getAssets()),

    GET("GET"),

    DELETE("DELETE"),

    PUT("PUT");



    private String method;



    Method(String s) {

        method = s;

    }



    private String getMethod() {

        return method;

    }

}

O/P:

    Hello World!

--------------

ssssssssssss

POST

POST

POST

All values of an Enumerator are singletons, which means, they are initialized once and reused every time you access it. So you can see the "definition" of an Enumerator Value as 'Constructor'.

This also means: if you provide a setter for the property "method" and change its value at runtime, the next access will return the new value! singleton does not mean its value is final.

public enum Method {

    POST(new Host().getAssets()), // definition

    GET("GET"),// definition

    DELETE("DELETE"),// definition

    PUT("PUT");// definition



    private String method;



    // Constructor

    Method(String s) {

        method = s;

    }



    private String getMethod() {

        return method;

    }

}