Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

Simple (?) problem with different classes

Posted on 2004-04-27
6
Medium Priority
?
183 Views
Last Modified: 2010-03-31
This looks like something I really should know, but Ive never had to deal with it until now...

Say i have 2 classes

class a()
   num=3
   classb.increase
   print num

class b()
   num++

the output will be 3, instead of 4. What am i doing wrong?

Thanks in advance


Full program listing:
***************************
class Networky  {
public int num=1;
      
      public Networky() {      }

      public void gameloop(){
      try{
      GameHandler gh = new GameHandler();
      gh.increase();
      System.out.println(num);
      }catch (Exception e) {}
      }

      public static void main(String args[]) {
            Networky mainFrame = new Networky();
            mainFrame.gameloop();                  
      }
}

class GameHandler extends Thread {

   public GameHandler () { }

   public void increase() {
        Networky net = new Networky();
            net.num++;
   }
}
0
Comment
Question by:hippydaz
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 2
6 Comments
 
LVL 37

Accepted Solution

by:
zzynx earned 100 total points
ID: 10932050
This prints "2":

class Networky  {
public int num=1;
     
     public Networky() {     }

     public void gameloop(){
     try{
     GameHandler gh = new GameHandler(this);
     gh.increase();
     System.out.println(num);
     }catch (Exception e) {}
     }

     public static void main(String args[]) {
          Networky mainFrame = new Networky();
          mainFrame.gameloop();              
     }
}

class GameHandler extends Thread {

   private Networky nw = null;
   public GameHandler (Networky networky) { nw = networky; }

   public void increase() {
          nw.num++;
   }
}
0
 
LVL 37

Expert Comment

by:zzynx
ID: 10932086
In increase() you just
1) created a *new* Networky instance
2) incremented its variable num
3) throw it away when leaving the function

You did never increment the num variable of the Networky instance called "mainFrame".
0
 

Author Comment

by:hippydaz
ID: 10932114
I knew it was getting increased then disappearing, but i had no idea why.

The explanation is slightly more complicated than i was expecting (i though i just wasnt declaring my integers properly or something) but thatll explain it.

Thanks.
0
Build and deliver software with DevOps

A digital transformation requires faster time to market, shorter software development lifecycles, and the ability to adapt rapidly to changing customer demands. DevOps provides the solution.

 
LVL 37

Expert Comment

by:zzynx
ID: 10932387
>> The explanation is slightly more complicated than i was expecting
But you do understand it?

Thanks for accepting.
That keeps us answering your future questions too.
0
 

Author Comment

by:hippydaz
ID: 10932552
>>But you do understand it?

More or less... I understand the concepts of how instances work, im just a bit fuzzy on creating instances as a whole. Ill understand the more i use them.
0
 
LVL 37

Expert Comment

by:zzynx
ID: 10936101
All right. Success.
0

Featured Post

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

INTRODUCTION Working with files is a moderately common task in Java.  For most projects hard coding the file names, using parameters in configuration files, or using command-line arguments is sufficient.   However, when your application has vi…
Are you developing a Java application and want to create Excel Spreadsheets? You have come to the right place, this article will describe how you can create Excel Spreadsheets from a Java Application. For the purposes of this article, I will be u…
Viewers learn about the “for” loop and how it works in Java. By comparing it to the while loop learned before, viewers can make the transition easily. You will learn about the formatting of the for loop as we write a program that prints even numbers…
This theoretical tutorial explains exceptions, reasons for exceptions, different categories of exception and exception hierarchy.
Suggested Courses

721 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question