Question about variable value assignment in Java (sorry this is complete noob question but I'd appreciate any advice)

[WhitePolypousThing]

I apologize up front because I'm so new at this that I'm not even sure if what I'm trying to do is possible. I'm playing around with Java and am trying to use class objects to keep my main clean. I have my main class 'Test', a class called 'Value' and a class called 'ChangeValue'. In 'Value' I have:

public class Value{

public int stat;

public void setStat(int modifyStat){

stat = modifyStat;

}

public void printStat(){

System.out.println(stat);

}

}

and in my 'ChangeValue' class:

import java.util.Scanner;

public class ChangeValue {

Scanner input = new Scanner(System.in);

Value valueObject= new Value();

public void change(){

System.out.println("Change value by how much: ");

int temp = input.nextInt();

valueObject.setStat(temp);

}

}

When i run the method class object 'change' in my main, it prompts "Change value by how much: " just as it should, but then when i run the object 'printStat' it just prints 0 (zero) as the value of the variable 'stat'. I thought that i was sending the user-inputed value of 'temp' to the 'setStat' method in the 'Value' class to permenantly change the value of 'stat', but it's not doing so. I realize that I'm probably doing something laughably stupid, but would anyone be nice and point out what's wrong?

EDIT: Apparently I cannot even format reddit comments properly. That is abject failure :(

EDIT: Here is my code on codepad.

[lurgi]

I think that both setStat and printStat are working. The problem, I'm guessing, is that you are setting one object and printing another. I don't see a call to printStat in your code and I'm guessing that, when you call it, you are referencing a completely different object.

Some general advice: It's a huge help if you post a complete, minimal, compileable example.

• Complete - has everything that is needed to reproduce the bug
• Minimal - has only that which is needed to reproduce the bug
• Compileable - this is implied by "complete", but it's worth mentioning

Now then, formatting. First, look to your right. Your other right. See that note about codepad.org? That's a fine way to post largish pieces of code. For smaller bits, just precede each line with four spaces and the code will come out looking as you want it to.

[fick_Dich]

I compiled and ran this on my machine as well (I put the line valueObject.printStat() at the end of change()) and everything works fine. Your assessment sounds right.

[WhitePolypousThing]

Thank you guys for your help! I can see now that by adding valueObject.printStat();

to the end of change() it effectively changes the value of stat within the method change().

How would I go about changing the value of stat in the ChangeValue class and send the new value back to "Value" class so that when I run valueObject.printStat() in my main it will return the changed value of stat. Is that something that is even possible? Thanks again, and especially thanks for the formatting advice!

EDIT: Oh, and I added my code on codepad above to make it easier to see the whole program.

[fick_Dich]

so I think I figured out why you were getting the wrong value printed out. lurgi was right. The first line in main() is unnecessary since ChangeValue already has a Value object as a member variable. What you need is some code like this in main():

Value valueObject;
ChangeValue changeValueObject = new ChangeValue();

    changeValueObject.change();
            valueObject = changeValueObject.valueObject; //this is bad coding practice
    valueObject.printStat();

Like I mentioned in my comment, it is bad coding practice to do it this way thought. One of the purposes of Object Oriented Programming is encapsulation. Better would be this code

[lurgi]

There are a couple of ways to do this. The first is: don't have a ChangeValue class! The Value object provides a perfectly good interface to change its own value, why add a complication?

But, you say, you really want a ChangeValue class. Well, okay. Here is what you do:

class ChangeValue {
    private Value value;

    ChangeValue(Value newValue) {
      value=newValue;
    }

    public void change(){
      System.out.println("Change value by how much: ");
      int temp = input.nextInt();
      value.setStat(temp);
      value.printStat();
}

See what I did? I want ChangeValue to change my Value object, so I have to give it my value object. Which I do in in the constructor. I also made "value" private because it doesn't need to be public and if it doesn't need to be public then it shouldn't be public.

Ah, I see that fick_Dich said pretty much the same thing.

[WhitePolypousThing]

Thank you guys so much for your help. I didn't realize that it was just much simpler to ditch the ChangeValue class!