Java example - NewVsSetLen.java

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/*
 * Copyright (C) The Apache Software Foundation. All rights reserved.
 *
 * This software is published under the terms of the Apache Software
 * License version 1.1, a copy of which has been included with this
 * distribution in the LICENSE.txt file.  */

package org.apache.log4j.performance;

/**

   This program compares the cost of creating a new StringBuffer and
   converting it to a String versus keeping the same StringBuffer,
   setting its size to zero and then converting it to String.

   The table below gives some figures.

   
   
     Total Message length
     0
     1
     2
     4
     8
   

   
     New Buffer  setLength 
     New Buffer  setLength
     New Buffer  setLength
     New Buffer  setLength
     New Buffer  setLength
   

    
   256 
   33 22 
   34 22
   34 22
   34 22 
   33 23
   

    
   1024 
   58 41
   59 45
   59 48
   59 51 
   60 44
   

    
   4096 
   146 132
   138 132
   144 126
   142 132
   136 132 
   

    
   16384 
   617 593 
   593 609
   601 617
   601 632 
   593 632
   

    
   65536 
   3218 3281
   3093 3125 
   3125 3156
   3125 3281 
   3062 3562
   

    
   262144 
   14750 15125
   14000 15500 
   14000 16125 
   14000 18000 
   14000 21375 
   

    
   1048576 
   87500 80000
   60500 82000 
   57000 93000 
   57500 118500 
   57500 168500 
   

   
Performance comparisons of new buffer
   creation versus setLength(0) approach for various message sizes and
   secondary loop lengths.
   
   

   
The tests copy a message to a destination string buffer and then
   copy a 256 character buffer to another buffer the number of times
   as specified by the secondary loop length.


   
The setLength(0) method is usually faster. However,
   after copying a large string it becomes slow even when copying
   small strings.


   
This is due to a peculiarity in the copy method in
   StringBuffer class which creates a character array of the same
   length as the old buffer even if the vast majority of those
   characters are unused. 

   
The tests were performed on Linux using IBM's JDK 1.1.8.

   
The test script is a crude model of what might happen in
   reality. If you remain unconvinced of its results, then please send
   your alternative measurement scenario.

   

   
*/
public class NewVsSetLen {

  static String s;

  static int BIGBUF_LEN = 1048576;
  static int SBUF_LEN = 256;
  static int RUN_LENGTH = BIGBUF_LEN/4;

  static char[] sbuf = new char[SBUF_LEN];
  static char[] bigbuf = new char[BIGBUF_LEN];

  {
    for(int i = 0; i < SBUF_LEN; i++) {
      sbuf[i] = (char) (i);
    }

    for(int i = 0; i < BIGBUF_LEN; i++) {
      bigbuf[i] = (char) (i);
    }
  }


  static
  public 
  void main(String[] args) {    
 
    int t;

    for(int len = SBUF_LEN; len <= BIGBUF_LEN; len*=4, RUN_LENGTH /= 4) {
      System.out.println("

"+len+"\n"); for(int second = 0; second < 16;) { System.out.println("SECOND loop="+second +", RUN_LENGTH=" +RUN_LENGTH+", len="+len); t = (int)newBuffer(len, second); System.out.print("

" + t); t = (int)setLen(len, second); System.out.println("

" + t + " \n"); if(second == 0) { second = 1; } else { second *= 2; } } } } static double newBuffer(int size, int second) { long before = System.currentTimeMillis(); for(int i = 0; i < RUN_LENGTH; i++) { StringBuffer buf = new StringBuffer(SBUF_LEN); buf.append(sbuf, 0, sbuf.length); buf.append(bigbuf, 0, size); s = buf.toString(); } for(int x = 0; x < second; x++) { StringBuffer buf = new StringBuffer(SBUF_LEN); buf.append(sbuf, 0, SBUF_LEN); s = buf.toString(); } return (System.currentTimeMillis() - before)*1000.0/RUN_LENGTH; } static double setLen(int size, int second) { long before = System.currentTimeMillis(); StringBuffer buf = new StringBuffer(SBUF_LEN); for(int i = 0; i < RUN_LENGTH; i++) { buf.append(sbuf, 0, sbuf.length); buf.append(bigbuf, 0, size); s = buf.toString(); buf.setLength(0); } for(int x = 0; x < second; x++) { buf.append(sbuf, 0, SBUF_LEN); s = buf.toString(); buf.setLength(0); } return (System.currentTimeMillis() - before)*1000.0/RUN_LENGTH; } }

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