Solved

Simple (?) problem with different classes

Posted on 2004-04-27
6
176 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
  • 4
  • 2
6 Comments
 
LVL 37

Accepted Solution

by:
zzynx earned 25 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
Are your AD admin tools letting you down?

Managing Active Directory can get complicated.  Often, the native tools for managing AD are just not up to the task.  The largest Active Directory installations in the world have relied on one tool to manage their day-to-day administration tasks: Hyena. Start your trial today.

 
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

ScreenConnect 6.0 Free Trial

Discover new time-saving features in one game-changing release, ScreenConnect 6.0, based on partner feedback. New features include a redesigned UI, app configurations and chat acknowledgement to improve customer engagement!

Question has a verified solution.

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

Suggested Solutions

For beginner Java programmers or at least those new to the Eclipse IDE, the following tutorial will show some (four) ways in which you can import your Java projects to your Eclipse workbench. Introduction While learning Java can be done with…
Introduction This article is the first of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article explains our test automation goals. Then rationale is given for the tools we use to a…
Viewers will learn about the different types of variables in Java and how to declare them. Decide the type of variable desired: Put the keyword corresponding to the type of variable in front of the variable name: Use the equal sign to assign a v…
Viewers will learn how to properly install Eclipse with the necessary JDK, and will take a look at an introductory Java program. Download Eclipse installation zip file: Extract files from zip file: Download and install JDK 8: Open Eclipse and …

778 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