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  1. #1
    mike1127 is offline Member
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    Default variables/data not in classes?

    I'm very new to Java. I'm used to putting variables and data definitions at the top level in a module; but I get syntax errors doing that in Java? Is there some standard way to provide data that's in a module or namespace but not part of a class?
    Thanks,
    Mike

  2. #2
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    Fubarable is offline Moderator
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    Default Re: variables/data not in classes?

    Everything *must* be in a class or similar top-level construct such as enum or interface.

  3. #3
    mike1127 is offline Member
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    Default Re: variables/data not in classes?

    Thanks. I have another question. Is the one-class-per-file restriction something in Java itself, or is that something Eclipse is forcing on me?

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    Default Re: variables/data not in classes?

    It's a Java restriction. Each file can have only one public top-level class, and that class must have the same name as the file.

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    wsaryada is offline Senior Member
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    Default Re: variables/data not in classes?

    And I think it is better not to use so many global variables in your code. Consider to use local variables more. If you have a large method, breaks it into a smaller chunk of code.

  6. #6
    mike1127 is offline Member
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    Default Re: variables/data not in classes?

    Quote Originally Posted by wsaryada View Post
    And I think it is better not to use so many global variables in your code. Consider to use local variables more. If you have a large method, breaks it into a smaller chunk of code.
    That's true, but I guess I'm coming from Haskell, which makes finer differentiations with the concepts of namespace, class, data, instance, and type, so it feels weird to me to make a class for something that there will only be one of. That's what I was thinking---there's only going to be one set of these variables. I guess in OO that's called the "singleton pattern"?

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    JosAH's Avatar
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    Default Re: variables/data not in classes?

    Quote Originally Posted by mike1127 View Post
    That's true, but I guess I'm coming from Haskell, which makes finer differentiations with the concepts of namespace, class, data, instance, and type, so it feels weird to me to make a class for something that there will only be one of. That's what I was thinking---there's only going to be one set of these variables. I guess in OO that's called the "singleton pattern"?
    The singleton pattern is just a small pattern (and over estimated); if you're absolutely, positively, definitely sure that you only need one 'thing' you can get away with a 'utility class', i.e. a class with just static methods (public) and optional static data (private); the class serves as a name space and nothing else. Java complicates matters a bit because the same class can be loaded by another class loader and you'll end up with more singleton objects or singleton utility classes ...

    kind regards,

    Jos
    The only person who got everything done by Friday was Robinson Crusoe.

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