Re: Class design

[cfowler <cfowler@outpostsentinel.com>]

Ed,

Maybe you can help me with this part.

I have 28 classes in one java file called ConfigDataTypes.java

The look like this

final class PortEntry{
}

final class UserEntry {
}


Thes are basically our representation of C structures that I use on the
embedded device.  However java doc complains there are no public classes
in this file.  Is this the correct way to do this?  I want the classes
to be available to anyone who needs them but not changeable.

Thanks,
Chris

On Tue, 2002-10-08 at 13:44, Ed Jenkins wrote:
> I used to optimized my fields like that too, when I moved from C++ to Java.  
> But I think the Java compiler is not bound to creating variables in the same 
> order as specified.  The compiler might rearrange and optimize them for you. 
>   And if you have more object references than primitive data types, then it 
> really doesn't matter.
> 
> I wouldn't worry too much about it, but here's something you might try.  
> Order them one way and compile it.  Note the file size of the compiled 
> .class file.  Change the order and compile again.  Compare sizes.  See if 
> anything changed in the physical layout of the class file.  This is not a 
> very useful trick, though, as the runtime implementation of the class will 
> differ from the class file representation, but you can try it and see what 
> happens.  You can find out what an object looks in memory by using a 
> debugger or by writing some reflection code, but it's still just a general 
> idea; I don't thing it is required to be accurate in regard to field order.  
> The real thing is a black box full of magic and you're not supposed to worry 
> about it.  A good profiler might be able to point out holes in memory 
> allocation, but I don't know for sure.
> 
> When in doubt, download the source code for the JDK and look at the compiler 
> and the classloader and see how they work.  Another excellent resource is 
> the book "Java Virtual Machine".
> 
> Ed
> 
> ---
> 
> From: cfowler <cfowler@outpostsentinel.com>
> To: ajug-members@ajug.org
> Subject: Class design
> Date: 08 Oct 2002 10:05:09 -0400
> 
> I'm creating classes for each of my structure types in my C program that
> will provide XML to the main program.  I want to make sure that I'm on
> the right track.  I want to keep these classes as small and tight as
> possible because it is possible for a 32 port device to have 32
> PortEntry objects.  If I have 100 x 32port devices then I will have 3200
> PortEntry objects accessible within one Java program.  Any suggestions
> would be appreciated.  I could expand the class to have methods of get
> and set for each variable  but then that would not be wise with memory
> usage in large number of objects.
> 
> 
> 
> final class PortEntry {
> 
>          public int number;      // Port Number
>          public String name;     // Port Name
>          public int speed;       // Port speed
>          public boolean modem;   // Modem enabled or disabled
>          public boolean bsIsDel; // Is Backspace Del?
>          public int trigger;     // Trigger record number
>          public int initrString; // Modem Init String
>          public int flow;        // Flow Control Settings
> 
> 
>          /**
>           * Function is an empty constructor
>           * That initializes the object
>           */
>          public PortEntry() {
> 
>                  // Init numbers
>                  flow = initrString = trigger = speed = number = 0;
> 
>                  // Init boolean values
>                  modem = bsIsDel = false;
> 
>                  // Init Strings
>                  name = "";
>          }
> 
>          /**
>           * Function will display the port number in the
>           * representation of a string
>           *
>           * @return      String  Port number in representatin of string
>           */
>          public String toString() {
> 
>                  // If number is 0 then this
>                  // class has not been populated
>                  // return a null
>                  if(number == 0)
>                          return null;
> 
>                  return "" + number;
>          }
> 
>          /**
>           * Function will return the string representation of
>           * the current flow settings
>           *
>           * @return      String  String representation of flow
>           */
>          public String getFlow() {
> 
>                  switch(flow) {
>                          case 1: return "software";
>                          case 2: return "hardware";
>                          case 3: return "none";
>                          default: return null;
>                  }
>          }
> 
> 
>          /**
>           * Function will return the state of modem being
>           * enabled on prot
>           *
>           * @return      boolean Modem enabled or disabled
>           */
>          public boolean isModem() {
>                  return modem;
>          }
> }
> 
> 
> Thanks,
> Chris Fowler
> 
> 
> _________________________________________________________________
> Chat with friends online, try MSN Messenger: http://messenger.msn.com
> 
> 
>