How to dynamically call static nested classes?

Question

I have the following java code:

...

public final class Constants {

    ...

    public static class Languages {
        ...
        
        public static class en_US {
            public static final String VALIDATION_REGEX = "[a-zA-Z-' ]+";
            ...
        }
        public static class en_GB {
            public static final String VALIDATION_REGEX = "[a-zA-Z-' ]+";
            ...
        }
    }

    ...
}

My problem is as follows: I receive a text and a language, and I have to check, whether that text is written only with valid alphabetic characters of that given language. My code so far is as follows:

...

public boolean isContentValid(String content, String language) {
    Boolean isCorrect = false;
    switch (language) {
        ...
        
        case "en_US":
            isCorrect = content.matches(Constants.Phrases.en_US.VALIDATION_REGEX);
            break;
        case "en_GB":
            isCorrect = content.matches(Constants.Phrases.en_GB.VALIDATION_REGEX);
            break;

        ...
        
        default:
            isCorrect = false;
    }
    return isCorrect;
}

...

This is fine and works, but as I add languages to my application, I will have to add more and more cases to my switch.

And I was wondering if in Java there is a way to dynamically name a static nested class, something like:

Constants.Phrases[language].VALIDATION_REGEX

So my above code could be something like:

...

public boolean isContentValid(String content, String language) {
    return content.matches(Constants.Phrases[language].VALIDATION_REGEX);
}

...

Thank you, and sorry if this is something super easy.

I am a JavaScript developer, and just learning Java.

Do you need to use classes? How about using Map<String, String> languageValidationRegexes which can map for instance "en_US" -> "[a-zA-Z-' ]+". With this you can write code like content.matches(languageValidationRegexes.get(language). — Pshemo
– Pshemo, Commented Feb 15, 2022 at 14:46

AkSh · Accepted Answer · 2022-02-15 16:17:02Z

1

Looking at you use case maybe this is a better approach:

public enum Language {
  en_US("engUS_reg"),
  en_GB("engGB_reg");

  private final String regex;

  Language(String regex) {
    this.regex = regex;
  }

  public String getRegex() {
    return regex;
  }
}

And using this enum class write your method as follows:

public boolean isContentValid(String content, String language) {
    return content.matches(Language.valueOf(language).getRegex());
}

answered Feb 15, 2022 at 16:17

AkSh

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1 Comment

einazare Over a year ago

Hello @AkSh. Thank you for your respone. Didn't think to use an enum. Thank you.

rhowell · Accepted Answer · 2022-02-15 15:03:19Z

0

You could use an enum for something like this.

"An enum can, just like a class, have attributes and methods. The only difference is that enum constants are public, static and final (unchangeable - cannot be overridden)." - [w3][1]

public enum Languages {
    EN_US {
        @Override
        public String toString() {
            return "[a-zA-Z-' ]+";
        }
    },
    EN_GB {
        @Override
        public String toString() {
            return "[a-zA-Z-' ]+";
        }
    },
}

And then you can access these values like this

Languages.valueOf("EN_US");

As mentioned by @Pshemo you could avoid a class based approach entirely and use an implementation of Map if you want something a little more lightweight

[1]: https://www.w3schools.com/java/java_enums.asp#:~:text=An%20enum%20can%2C%20just%20like,but%20it%20can%20implement%20interfaces).

edited Feb 15, 2022 at 15:03

answered Feb 15, 2022 at 14:51

rhowell

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1 Comment

einazare Over a year ago

Hello @rhowel. Thank you for jumping in. I think I will change my class approach to this one.

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