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Thread: Transfering Variables across classes.

  1. #1
    Junior Member
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    Default Transfering Variables across classes.

    Class 1:

    view sourceprint?
    1 public class one {

    2 public static void main(String[] args){

    3 int num = 0;

    4 System.out.println(num);

    5 two.change(num);

    6 System.out.println(num);

    7 }

    8 }

    Class 2:
    view sourceprint?
    1 public class two {

    2 static void change(int num){

    3 num = num + 1;

    4 }


    This should print 0, then 1, but it prints 0, then 0. How do I make it print 0 then 1 with the same format?

  2. #2
    Member Ada Lovelace's Avatar
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    Default Re: Transfering Variables across classes.

    That code is very hard to read, but from what I can gather, there is no
    instance of class two being created, so your call to:

    Should of caused an error. Both classes I am assuming are also in separate source files,
    so make sure they each have the same package name so the compiler knows where to find
    the methods of each class when they are invoked.

    Thirdly, Java does not pass values by reference, only by value. Hence if you passed 'num'
    to class two;s method which attempts to increment it by one, the change would happen in
    that method, but when control is returned to first method to print out the result, the original
    value of 'num' is the same - hence why it is printing zero.

    One way around this is to create an array holding the value, and pass that to the method then modify
    the index. Array's are passed by reference, class objects by pointer reference.

    Wishes Ada xx
    If to Err is human - then programmers are most human of us all.
    "The Analytical Engine offers a new, a vast, and a powerful language . . .
    for the purposes of mankind
    Augusta Ada Byron, Lady Lovelace (1851)

  3. #3
    Super Moderator
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    So. Maryland, USA
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    Default Re: Transfering Variables across classes.

    Welcome to the forum! Please read this topic to learn how to post code in code or highlight tags and other useful info for new members.

    Please post your code correctly using code or highlight tags per the above link.

    How did you come by this code? Did you just think of it? It's an interesting study that you should play around with to gain a better understanding of how classes and methods work together - or don't. Play with nested classes, static nested classes and inner classes, static/non-static methods, etc. You can find out more about these topics in the Oracle Tutorials.

  4. #4
    Grand Poobah
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    Default Re: Transfering Variables across classes.

    Quote Originally Posted by Ada Lovelace View Post
    so your call to:

    Should of caused an error.
    The change method is static so the code compiles fine. Of course had the OP adhered to naming conventions and called the class Two it would have been easier to read.
    Improving the world one idiot at a time!

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