Re: Why is Java so slow????

Java Performance Expert wrote:


I poked around the Java sources and did some experimentation. Removing
object creation does seem to help. So does removing casting at runtime,
including casting primitives.

Here's my own version, based loosely on the Integer.toString(int) method
source.

/** Converts a POSITIVE integer to a byte [], with an emphasis on speed.
  *
  * @param buff The start, length and ASCII values are stored in this
  * buffer.
  * The buffer must be therefore at least the size of Integer.MAX_VALUE +
  * 2.
  * buff.start stores the offset of the first ASCII character.
  * buff.length
  * stores
  * the length of the ASCII character string. Strings are written to the
  * end of the buffer.ascii array.
  * @param i MUST BE POSITIVE. This is not tested by the method. Stuff
  * will explode in spectacular ways if you pass this routine a negative
  * integer.
  */
     static void fastItoS2( AsciiByteBuff buff, int i ) {
         int index = buff.ascii.length - 1;
         int q = i;
         int r;
         for(;;) {
             r = q % 10;
             q = q / 10;
             buff.ascii[index--] = digits[r];
             if( q == 0 )
                 break;
         }
         buff.start = (index + 1);
         buff.slength = (buff.ascii.length - 1 - index);
     }

     private static class AsciiByteBuff {
         public int start;
         public int slength;
         public byte [] ascii;
     }

     private static byte [] digits = { '0', '1', '2', '3', '4', '5', '6',
             '7', '8', '9' };

Here is the driver for this routine:

     static public void write3fastItoS2( String[] args ) throws
IOException {

         int lim = DEFAULT_LINES;

         if( args != null && args.length > 0 ) {
             try {
                 lim = Integer.parseInt( args[0] );
             } catch( NumberFormatException ex ) {
                 System.err.print( ex + "\nUsing default of " +
DEFAULT_LINES );
             }
             if( lim < 0 ) {
                 lim = DEFAULT_LINES;
                 System.err.println( "Lim less than 0.\n"
                   + "Using defalut of " + DEFAULT_LINES );
             }
         }

         BufferedOutputStream os = new BufferedOutputStream( System.out );

         String message2 = "This is line ";
         byte[] mbuff = message2.getBytes();
         int mlength = mbuff.length;

         AsciiByteBuff ibuff = new AsciiByteBuff();
         ibuff.ascii = new byte
[Integer.toString(Integer.MIN_VALUE).length()
                 + 2 ];

         for( int i = 0; i < lim; i++ ) {
             // os.write( mbuff );
             os.write( mbuff, 0, mlength );
             fastItoS2( ibuff, i );
             os.write(ibuff.ascii, ibuff.start, ibuff.slength );
             os.write('\n');
         }
         os.close();
     }

I think that's right, I had to repair a couple of lines after the email
editor wrapped them.

Good luck.