C structure in JAVA equavilent

JAVA

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  • 1. Delete used variables....
    Say if memory was a problem (limited capacity) and I needed to use as few variables as possible. I know you can just override and reuse earlier used variables but is there an actual way to destroy a variable after its been used in a method? e.g something like variable_x.delete(). Thanks, Peter
  • 2. memory requirements
    I am running a graphic analysis modeling app that has three means to run : batch , brower, VBscript. It used to run fine, but after running once now, it bombs out in any mode. It will also run with a small input series of data points (60), but bombs out if I triple the input (180), as tho it ran out of RAM. There are some functions which won't run under any circumstances. There is a status bar at bottom of the app which shows calculations in progress, but it ends quickly when it bombs out. I have 1GB RAM running XP sp2 and latest JAVA runtime I have seen the terms "heap" and "stack" memory, pagefile size, and I am looking for system settings that may have gotten screwed up sometime in the past. What should I be looking for in system settings? TIA, Stew Corman from sunny Endicott

C structure in JAVA equavilent

Postby oo » Wed, 09 Jul 2003 17:29:23 GMT

I am doing this in c/c++:

struct MY_REC
{
   short nLen;
   char  szName[9];
} myRec;

myRec.nLen = 9;
strcpy(myRec.Name, "Superman");

write(&myRec, sizeof MY_REC);

The write() function will take the address of myRec and write the whole
structure to file. The binary value of nLen will be wriiten to file.

How can I achieve this in Java?

Re: C structure in JAVA equavilent

Postby Joseph Millar » Wed, 09 Jul 2003 19:25:21 GMT




See the java.io.Serializable interface and its use in the API docs.

Also, there is nothing to prevent you having a read() and write()
method as part of your class that know now to dump/get saved state
information.

--Joe

Re: C structure in JAVA equavilent

Postby Steve Horsley » Wed, 09 Jul 2003 19:32:21 GMT




I asume you want to write a compatible file in java?

First you need to specify the exact file format:
* What characterset / text encoding scheme does the file use?
  Is is ASCII, CP2125, 8859-1 etc.
* What encoding does the short use?
  How many bytes, and in what order? Is it signed?
* What happens if the name is <> than 8 characters?

Use shift-and-mask to make up the bytes for the short.
Use String.getBytes(String encoding) to get the string bytes
Don't forget to write the trailing zero byte.

e.g. 
    byte[] stringBytes = name.getBytes("ISO8859-1");
    byte msb = (byte) ((nLen >> 8) & 0xFF);
    byte lsb = (byte) (nLen & 0xfF);
    myOutputStream.write(msb);
    myOutputStream.write(lsb);
    myOutputStream.write(stringBytes);
    myOutputStream.write((byte) 0);

Steve


Re: C structure in JAVA equavilent

Postby Jon A. Cruz » Thu, 10 Jul 2003 01:09:28 GMT



Chances are the C code is broken and you don't even know it.

That's a *very* bad thing to do. When you write C/C++ code like that, 
you get broken results. Running on different types of computers will 
break it. Compiling with different switches will break it. Compiling 
with different compilers might break it. Even using all the exact same 
settings, but a newer version of the same compiler from the same vendor 
might break it.

*Never* read and write structs directly.




Write clean, proper C code. The write the same code in Java. It can end
up almost identical.


Follow the advice from Steve Horsley in doing this.


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