random access file!

[khajeddin]

hi: how can get various size to a random access file progarm .
i mean i have read that we should give a costant size tu constructor ,is it ture?

[JosAH]

hi: how can get various size to a random access file progarm .
i mean i have read that we should give a costant size tu constructor ,is it ture?

I apologize, I don't understand what you're trying to say. Random access files
are files that you can read from or write to just like ordinary streams and on top
of that you can position a file pointer telling the random access file where to
read from or from where to write to. Care to rephrase your question? thanks.

kind regards,

Jos

[khajeddin]

well, i'v read some where that for creating a random access file we should spesify an exact size for every record which we want to keep.
for example if we want to create a file which can take 100 record and every record will occure 32 byte (at maximom size),we should give this size(32 byte) to the program.it means after finishing the program we can't have a record with size of 42 byte.
now my question is : is it any way that we can make random access file which make it posible to write records with different size of byte,without risrict the program foe a maximom size?
here is an example of a program with ristrict size of records:

 4
 5  import java.io.RandomAccessFile;
 6  import java.io.IOException;     
 7
 8  public class RandomAccessAccountRecord extends AccountRecord
 9  {
10      public static final int SIZE = 72;//here a size of records is spesified
11
12     // no-argument constructor calls other constructor with default values
13     public RandomAccessAccountRecord()
14     {
15        this ( 0, "", "", 0.0 );
16     } // end no-argument RandomAccessAccountRecord constructor
17
18     // initialize a RandomAccessAccountRecord
19     public RandomAccessAccountRecord( int account, String firstName,
20        String lastName, double balance )
21     {
22        super( account, firstName, lastName, balance );
23     } // end four-argument RandomAccessAccountRecord constructor
24
25     // read a record from specified RandomAccessFile
26     public void read( RandomAccessFile file ) throws IOException
27     {
28        setAccount( file.readInt() );
29        setFirstName( readName( file ) );
30        setLastName( readName( file ) );
31        setBalance( file.readDouble() );
32     } // end method read
33
34     // ensure that name is proper length
35     private String readName( RandomAccessFile file ) throws IOException
36     {
37        char name[] = new char[ 15 ], temp;
38
39        for ( int count = 0; count < name.length; count++ )
40        {
41           temp = file.readChar();
42           name[ count ] = temp;
43        } // end for
44
45        return new String( name ).replace( '\0', ' ' );
46     } // end method readName
47
48     // write a record to specified RandomAccessFile
49     public void write( RandomAccessFile file ) throws IOException
50     {
51        file.writeInt( getAccount() );
52        writeName( file, getFirstName() );
53        writeName( file, getLastName() );
54        file.writeDouble( getBalance() );
55     } // end method write
56
57     // write a name to file; maximum of 15 characters
58     private void writeName( RandomAccessFile file, String name )
59        throws IOException                                       
60     {
61        StringBuffer buffer = null;
62
63        if ( name != null )
64           buffer = new StringBuffer( name );
65        else
66           buffer = new StringBuffer( 15 );
67
68        buffer.setLength( 15 );
69        file.writeChars( buffer.toString() );
70     } // end method writeName
71  } // end class RandomAccessAccountRecord
 

 
 8  public class CreateRandomFile
 9  {
10     private static final int NUMBER_RECORDS = 100;
11
12     // enable user to select file to open
13     public void createFile()
14     {
15        RandomAccessFile file = null;
16
17        try // open file for reading and writing
18        {
19           file = new RandomAccessFile( "clients.dat", "rw" );
20
21           RandomAccessAccountRecord blankRecord =
22              new RandomAccessAccountRecord();
23
24           // write 100 blank records
25           for ( int count = 0 ; count < NUMBER_RECORDS; count++ )
26              blankRecord.write( file );
27
28           // display message that file was created
29           System.out.println( "Created file clients.dat." );
30
31           System.exit( 0 ); // terminate program
32        } // end try
33        catch ( IOException ioException )
34        {
35           System.err.println( "Error processing file." );
36           System.exit( 1 );
37        } // end catch
38        finally
39        {
40           try
41           {
42              if ( file != null )
43                 file.close(); // close file
44           } // end try
45           catch ( IOException ioException )
46           {
47              System.err.println( "Error closing file." );
48              System.exit( 1 );
49           } // end catch
50        } // end finally
51     } // end method createFile
52  } // end class CreateRandomFile
 
 

[JosAH]

well, i'v read some where that for creating a random access file we should spesify an exact size for every record which we want to keep.
for example if we want to create a file which can take 100 record and every record will occure 32 byte (at maximom size),we should give this size(32 byte) to the program.it means after finishing the program we can't have a record with size of 42 byte.

Nonono, those were the days when IBM's VM (*), CMS, dinosaurs, mammoths
and Marylin Monroe ruled the word. Think of a random access file as a semi-infinite
sequence of bytes and a little finger; the little finger points to the current file
position and you can read or write anything you want starting at the position to
which that little fingers points.

now my question is : is it any way that we can make random access file which make it posible to write records with different size of byte,without risrict the program foe a maximom size?

Yep, see above; nothing on earth prohibits you to do that.

kind regards,

Jos

(*) nice thing, VM; a bit of an anachronism in those days though.

[khajeddin]

well how can i do that ,in the above programs if i don't write the line:

public static final SIZE 72;

does the program run correctly????
if i create a random access file without ristriction,while using the program and updating a record( for example add some information to the record)doesn't it distibute the date of th next record?
and in this condition how can i access to a record (because now i don't know howmany bytesi should move forward! )?