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ProGuard is a free shrinker, optimizer, obfuscator, and preverifier for Java bytecode
There is a newer version: 7.6.0
/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2022 Guardsquare NV
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.obfuscate;

import java.util.Arrays;

/**
 * This NameFactory generates unique short names, using mixed-case
 * characters or lower-case characters only.
 *
 * @author Eric Lafortune
 */
public class SimpleNameFactory implements NameFactory
{
    private static final int CHARACTER_COUNT = 26;

    /**
     +     * Array of windows reserved names.
     +     * This array does not include COM{digit} or LPT{digit} as {@link SimpleNameFactory} does not generate digits.
     +     * This array must be sorted in ascending order as we're using {@link Arrays#binarySearch(Object[], Object)} on it.
     +     */
    private static final String[] reservedNames    = new String[] {"AUX", "CON", "NUL", "PRN"};

    private final boolean generateMixedCaseNames;
    private int     index = 0;

    /**
     * Creates a new SimpleNameFactory that generates mixed-case names.
     */
    public SimpleNameFactory()
    {
        this(true);
    }


    /**
     * Creates a new SimpleNameFactory.
     * @param generateMixedCaseNames a flag to indicate whether the generated
     *                               names will be mixed-case, or lower-case only.
     */
    public SimpleNameFactory(boolean generateMixedCaseNames)
    {
        this.generateMixedCaseNames = generateMixedCaseNames;
    }


    // Implementations for NameFactory.

    public void reset()
    {
        index = 0;
    }


    public String nextName()
    {
        return name(index++);
    }


    /**
     * Returns the name at the given index.
     */
    private String name(int index)
    {
        // Create a new name for this index
        return newName(index);
    }


    /**
     * Creates and returns the name at the given index.
     */
    private String newName(int index)
    {
        // If we're allowed to generate mixed-case names, we can use twice as
        // many characters.
        int totalCharacterCount = generateMixedCaseNames ?
            2 * CHARACTER_COUNT :
            CHARACTER_COUNT;

        int baseIndex = index / totalCharacterCount;
        int offset    = index % totalCharacterCount;

        char newChar = charAt(offset);

        String newName = baseIndex == 0 ?
            new String(new char[] { newChar }) :
            (name(baseIndex-1) + newChar);

        if (Arrays.binarySearch(reservedNames, newName.toUpperCase()) >= 0)
        {
            newName += newChar;
        }
        return newName;
    }


    /**
     * Returns the character with the given index, between 0 and the number of
     * acceptable characters.
     */
    private char charAt(int index)
    {
        return (char)((index < CHARACTER_COUNT ? 'a' - 0               :
                                                 'A' - CHARACTER_COUNT) + index);
    }


    public static void main(String[] args)
    {
        System.out.println("Some mixed-case names:");
        printNameSamples(new SimpleNameFactory(true), 60);
        System.out.println("Some lower-case names:");
        printNameSamples(new SimpleNameFactory(false), 60);
        System.out.println("Some more mixed-case names:");
        printNameSamples(new SimpleNameFactory(true), 80);
        System.out.println("Some more lower-case names:");
        printNameSamples(new SimpleNameFactory(false), 80);
    }


    private static void printNameSamples(SimpleNameFactory factory, int count)
    {
        for (int counter = 0; counter < count; counter++)
        {
            System.out.println("  ["+factory.nextName()+"]");
        }
    }
}