Re: StringBuffer/StringBuilder efficiency

Roedy Green <>
Wed, 30 Sep 2009 18:24:07 -0700
On Wed, 30 Sep 2009 17:42:29 -0700, Roedy Green
<> wrote, quoted or indirectly quoted
someone who said :

I think my next step is to write the code for a new String constructor
new String( String... )
and see if I can sell Sun on including it, and persuading Javac to use
that method to implement the + operator.

 * @(#)
 * Summary: Demonstrate how a new efficient concatenating String
constructor would work.
 * Copyright: (c) 2009 Roedy Green, Canadian Mind Products,
 * Licence: This software may be copied and used freely for any
purpose but military.
 * Requires: JDK 1.6+
 * Created with: IntelliJ IDEA IDE.
 * Version History:
 * 1.0 2009-09-29 - initial release

package com.mindprod.fastcat;

 * Demonstrate how a new efficient concatenating String constructor
would work.
 * Constructor permits more efficient concatenation than StringBuffer
or StringBuilder.
 * It uses no intermediate buffers and no intermediate character
 * It might be used to more efficiently implement the + concatenation
operator and StringWriter.
 * Why bother? Webservers do almost nothing but concatenate Strings
and garbage collection.
 * @author Roedy Green, Canadian Mind Products
 * 1.0 2009-09-30 - initial release
 * @since 2009-09-30
public class DummyString
    // ------------------------------ FIELDS

     * The value is used for character storage.
    private final char value[];

     * The count is the number of characters in the String.
    private final int count;

     * The offset is the first index of the storage that is used.
    private final int offset;

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

     * Initializes a newly created {@code String} object so that it
     * an empty character sequence. Note that use of this constructor
     * unnecessary since Strings are immutable.
    public DummyString()
        this.offset = 0;
        this.count = 0;
        this.value = new char[0];

     * concatenating String constructor
     * @param pieces vararg of Strings to be concatenated to create
this new String.
    public DummyString( String... pieces )
        offset = 0;
        int joinedLength = 0;
        /** find out how big a buffer we need to contain all the
joined Strings */
        for ( String piece : pieces )
            joinedLength += piece.length();

        // allocate buffer for joined pieces. This becomes the new
        count = joinedLength;
        value = new char[joinedLength];
        // copy over all the pieces into the slot in the joined buffer
        int position = 0;
        for ( String piece : pieces )
            final int length = piece.length();
            // copy piece into buffer with System.arraycopy
            piece.getChars( 0, length, value, position );
            position += length;
Roedy Green Canadian Mind Products

There is one brain organ that is optimised for understanding and articulating logical processes, and that is the outer layer of the brain, called the cerebral cortex. Unlike the rest of the brain, this relatively recent evolutionary development is rather flat, only about 0.32 cm (0.12 in) thick, and includes a mere 6 million neurons. This elaborately folded organ provides us with what little competence we do possess for understanding what we do and who we do it.
~ Ray Kurzweil (born: 1948-02-12 age: 61)

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