Re: StringBuffer/StringBuilder efficiency

On Sun, 27 Sep 2009 20:48:55 +0100, Tom Anderson
<twic@urchin.earth.li> wrote, quoted or indirectly quoted someone who
said :


Here is one implementation of a Fast Concatenate to replace
StringBuilder. It needs two speedups, I don't know are possible
without some sort of hack. It would be nice if String had a String...
constructor to avoid the creation of two buffers and an extra copy.

/*
 * @(#)FastCat.java
 *
 * Summary: Stripped down, fast replacement for StringBuilder and
StringWriter to build concatentated Strings.
 *
 * Copyright: (c) 2009 Roedy Green, Canadian Mind Products,
http://mindprod.com
 *
 * Licence: This software may be copied and used freely for any
purpose but military.
 * http://mindprod.com/contact/nonmil.html
 *
 * Requires: JDK 1.6+
 *
 * Created with: IntelliJ IDEA IDE.
 *
 * Version History:
 * 1.0 2009-09-29 - initial release

 */
package com.mindprod.fastcat;

import java.io.File;
import java.util.ArrayList;

/**
 * Stripped down, fast replacement for StringBuilder and StringWriter
to build concatentated Strings.
 *
 * @author Roedy Green, Canadian Mind Products
 * 1.0 2009-09-29 - initial release
 * @since 2009-09-29
 */

public class FastCat
    {
    // ------------------------------ FIELDS
------------------------------

    /**
     * private collection of pieces we will later glue together once
we know the size of the final String
     */
    final ArrayList<String> pieces;

    private int length = 0;

    // -------------------------- PUBLIC INSTANCE METHODS
--------------------------

    /**
     * no-arg constructor
     */
    public FastCat()
        {
        pieces = new ArrayList<String>( 20 );
        }

    /**
     * constructor
     *
     * @param estNumberOfPieces estimated number of chunks you will
concatenate. It is better to estimate slightly high than slightly
low.
     */
    public FastCat( int estNumberOfPieces )
        {
        pieces = new ArrayList<String>( estNumberOfPieces );
        }

    /**
     * append String
     *
     * @param s String to append
     */
    public void append( String s )
        {
        length += s.length();
        pieces.add( s );
        }

    /**
     * append arbitrary number of strings
     *
     * @param ss comma-separated list of Strings to append
     */
    public void append( String... ss )
        {
        for ( String s : ss )
            {
            length += s.length();
            pieces.add( s );
            }
        }

    /**
     * append Object
     *
     * @param o Object to append. toString is called to acquire a
String to concatenate.
     */
    public void append( Object o )
        {
        final String s = o.toString();
        length += s.length();
        pieces.add( s );
        }

    /**
     * append arbitrary number of Objects
     *
     * @param ,, comma-separated list of Objects to to append.
toString is called to acquire a String to concatenate.
     */
    public void append( Object... oo )
        {
        for ( Object o : oo )
            {
            final String s = o.toString();
            length += s.length();
            pieces.add( s );
            }
        }

    /**
     * empty the concatenated String being created
     */
    public void clear()
        {
        pieces.clear();
        }

    /**
     * Get the concatenation of all the strings appended so far
     */
    public String toString()
        {
        int offset = 0;
        final char[] buffer = new char[length];
        for ( String p : pieces )
            {
            for ( int i = 0; i < p.length(); i++ )
                {
                // copy over that once piece, char by char. Can this
be improved?
                buffer[ offset++ ] = p.charAt( i );
                }
            }
        return new String( buffer ); // Would like some way to just
hand buffer over to String to avoid copy.
        }

    // --------------------------- main() method
---------------------------

    /**
     * test harness
     *
     * @param args not used.
     */
    public static void main( String[] args )
        {
        FastCat f = new FastCat( 7 );
        f.append( "Hello" );
        f.append( " " );
        f.append( "World. " );
        f.append( new File( "temp.txt" ) );
        f.append( " " ,"abc", "def" );
        System.out.println( f.toString() );
        // prints Hello World. temp.txt abcdef
        }
    }
--
Roedy Green Canadian Mind Products
http://mindprod.com

On two occasions I have been asked [by members of Parliament], "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.
~ Charles Babbage (born: 1791-12-26 died: 1871-10-18 at age: 79)