Why do I have to declare the constants stati - java help on CodeGym

Why do I have to declare the constants static also? I don't understand.

public class Solution {

    public final class Constants {
        public static final String SERVER_IS_CURRENTLY_NOT_ACCESSIBLE = "The server is currently not accessible.";
        public static final String USER_IS_NOT_AUTHORIZED = "The user is not authorized";
        public static final String USER_IS_BANNED = "The user is banned";
        public static final String ACCESS_IS_DENIED = "Access is denied";
    }

    public class ServerNotAccessibleException extends Exception {
        public ServerNotAccessibleException() {
            super("The server is currently not accessible.");
        }

        public ServerNotAccessibleException(Throwable cause) {
            super("The server is currently not accessible.", cause);
        }
    }

    public class UnauthorizedUserException extends Exception {
        public UnauthorizedUserException() {
            super("The user is not authorized.");
        }

        public UnauthorizedUserException(Throwable cause) {
            super("The user is not authorized.", cause);
        }
    }

    public class BannedUserException extends Exception {
        public BannedUserException() {
            super("The user is banned.");
        }

        public BannedUserException(Throwable cause) {
            super("The user is banned.", cause);
        }
    }

    public class RestrictionException extends Exception {
        public RestrictionException() {
            super("Access is denied.");
        }

        public RestrictionException(Throwable cause) {
            super("Access is denied.", cause);
        }
    }

    public static void main(String[] args) {

    }
}

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Guadalupe Gagnon

Level 37 , Tampa, United States

5 April 2021, 15:00

useful

There are two good reasons to make a variable static: - The first, which doesn't really apply to this task but I will mention anyways, is so that only 1 block of memory is taken to store the size of the variable no matter how many objects are created. A variable that is the same no matter how many objects are created doesn't need its own memory blocked out for each object created. but - in this task the reason to make them static is so that you don't even need to create an object to use them since static variables don't need an object to be created for access. This task is just demonstrating the use of a class as a container to hold your final variables. This is actually very handy when you have messages like this that could appear in multiple points in the code. Let's say you created a program like this, but had thousands of lines of code instead, and then management wanted to change the phrases. You would only have to change those couple of lines instead of going through ALL your code and changing each line that contains one of the phrases. An actual example would be if you wanted to use this code but change the language from English to Spanish (or French, or Russian, or Japanese... etc).

Andrei

Level 41

5 April 2021, 15:13

OK, then why not just declare them in a static block? Because I wouldn't be able to access and modify them like you mentioned in the example?

5 April 2021, 15:49

solution

That is because the code should be written like this:

// one example, but all the code should mirror this
public ServerNotAccessibleException() {
   super(Constants.SERVER_IS_CURRENTLY_NOT_ACCESSIBLE);
}

That is how a container class is supposed to be used and that is where it is valuable. The above task is a small example, but typically in the real world, the container class would be in a separate file completely and could be accessed by ALL the code through multiple files. I bet you have never made a small spelling mistake over the same line like this: "Acess is denied." "Access is denied." "Access is denied" "Access is denied." "Access is dened." "Acces is denied." In the task above, no big deal because there are only 30 lines of code, but imagine working at Facebook, which has over 10 million lines of code. Would you like to search those 10 million lines looking for spelling mistakes?.... or go directly to the container class where String literals are stored?

5 April 2021, 16:16

Ahh, OK, so they are connected to something else that needs to access them. Got it, thanks! 👍