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 *    any, must include the following acknowledgement:
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package org.apache.commons.lang;

import java.util.Random;
/**
 * <p>Operations for random <code>String</code>s.</p>
 *
 * @author GenerationJava Core library
 * @author <a href="mailto:bayard@generationjava.com">Henri Yandell</a>
 * @author <a href="mailto:steven@caswell.name">Steven Caswell</a>
 * @author Stephen Colebourne
 * @author Gary Gregory
 * @author Phil Steitz
 * @since 1.0
 * @version $Id: RandomStringUtils.java,v 1.1 2012/08/30 16:24:42 marcin Exp $
 */
public class RandomStringUtils {

    /**
     * <p>Random object used by random method. This has to be not local
     * to the random method so as to not return the same value in the 
     * same millisecond.</p>
     */
    private static final Random RANDOM = new Random();

    /**
     * <p><code>RandomStringUtils</code> instances should NOT be constructed in
     * standard programming. Instead, the class should be used as
     * <code>RandomStringUtils.random(5);</code>.</p>
     *
     * <p>This constructor is public to permit tools that require a JavaBean instance
     * to operate.</p>
     */
    public RandomStringUtils() {
    }

    // Random
    //-----------------------------------------------------------------------
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of all characters.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String random(int count) {
        return random(count, false, false);
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of characters whose
     * ASCII value is between <code>32</code> and <code>126</code> (inclusive).</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomAscii(int count) {
        return random(count, 32, 127, false, false);
    }
    
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of alphabetic
     * characters.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomAlphabetic(int count) {
        return random(count, true, false);
    }
    
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of alpha-numeric
     * characters.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomAlphanumeric(int count) {
        return random(count, true, true);
    }
    
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of numeric
     * characters.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomNumeric(int count) {
        return random(count, false, true);
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of alpha-numeric
     * characters as indicated by the arguments.</p>
     *
     * @param count  the length of random string to create
     * @param letters  if <code>true</code>, generated string will include
     *  alphabetic characters
     * @param numbers  if <code>true</code>, generatd string will include
     *  numeric characters
     * @return the random string
     */
    public static String random(int count, boolean letters, boolean numbers) {
        return random(count, 0, 0, letters, numbers);
    }
    
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of alpha-numeric
     * characters as indicated by the arguments.</p>
     *
     * @param count  the length of random string to create
     * @param start  the position in set of chars to start at
     * @param end  the position in set of chars to end before
     * @param letters  if <code>true</code>, generated string will include
     *  alphabetic characters
     * @param numbers  if <code>true</code>, generated string will include
     *  numeric characters
     * @return the random string
     */
    public static String random(int count, int start, int end, boolean letters, boolean numbers) {
        return random(count, start, end, letters, numbers, null, RANDOM);
    }

    /**
     * <p>Creates a random string based on a variety of options, using
     * default source of randomness.</p>
     *
     * <p>This method has exactly the same semantics as
     * {@link #random(int,int,int,boolean,boolean,char[],Random)}, but
     * instead of using an externally supplied source of randomness, it uses
     * the internal static {@link Random} instance.</p>
     *
     * @param count  the length of random string to create
     * @param start  the position in set of chars to start at
     * @param end  the position in set of chars to end before
     * @param letters  only allow letters?
     * @param numbers  only allow numbers?
     * @param chars  the set of chars to choose randoms from.
     *  If <code>null</code>, then it will use the set of all chars.
     * @return the random string
     * @throws ArrayIndexOutOfBoundsException if there are not
     *  <code>(end - start) + 1</code> characters in the set array.
     */
    public static String random(int count, int start, int end, boolean letters, boolean numbers, char[] chars) {
        return random(count, start, end, letters, numbers, chars, RANDOM);
    }

    /**
     * <p>Creates a random string based on a variety of options, using
     * supplied source of randomness.</p>
     *
     * <p>If start and end are both <code>0</code>, start and end are set
     * to <code>' '</code> and <code>'z'</code>, the ASCII printable
     * characters, will be used, unless letters and numbers are both
     * <code>false</code>, in which case, start and end are set to
     * <code>0</code> and <code>Integer.MAX_VALUE</code>.
     *
     * <p>If set is not <code>null</code>, characters between start and
     * end are chosen.</p>
     *
     * <p>This method accepts a user-supplied {@link Random}
     * instance to use as a source of randomness. By seeding a single 
     * {@link Random} instance with a fixed seed and using it for each call,
     * the same random sequence of strings can be generated repeatedly
     * and predictably.</p>
     *
     * @param count  the length of random string to create
     * @param start  the position in set of chars to start at
     * @param end  the position in set of chars to end before
     * @param letters  only allow letters?
     * @param numbers  only allow numbers?
     * @param chars  the set of chars to choose randoms from.
     *  If <code>null</code>, then it will use the set of all chars.
     * @param random  a source of randomness.
     * @return the random string
     * @throws ArrayIndexOutOfBoundsException if there are not
     *  <code>(end - start) + 1</code> characters in the set array.
     * @throws IllegalArgumentException if <code>count</code> &lt; 0.
     * @since 2.0
     */
    public static String random(int count, int start, int end, boolean letters, boolean numbers, char[] chars, Random random) {
        if (count == 0) {
            return "";
        } else if (count < 0) {
            throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
        }
        if ((start == 0) && (end == 0)) {
            end = 'z' + 1;
            start = ' ';
            if (!letters && !numbers) {
                start = 0;
                end = Integer.MAX_VALUE;
            }
        }

        StringBuffer buffer = new StringBuffer();
        int gap = end - start;

        while (count-- != 0) {
            char ch;
            if (chars == null) {
                ch = (char) (random.nextInt(gap) + start);
            } else {
                ch = chars[random.nextInt(gap) + start];
            }
            if ((letters && numbers && Character.isLetterOrDigit(ch))
                || (letters && Character.isLetter(ch))
                || (numbers && Character.isDigit(ch))
                || (!letters && !numbers)) {
                buffer.append(ch);
            } else {
                count++;
            }
        }
        return buffer.toString();
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of characters
     * specified.</p>
     *
     * @param count  the length of random string to create
     * @param chars  the String containing the set of characters to use,
     *  may be null
     * @return the random string
     * @throws IllegalArgumentException if <code>count</code> &lt; 0.
     */
    public static String random(int count, String chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, chars.toCharArray());
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of characters specified.</p>
     *
     * @param count  the length of random string to create
     * @param chars  the character array containing the set of characters to use,
     *  may be null
     * @return the random string
     * @throws IllegalArgumentException if <code>count</code> &lt; 0.
     */
    public static String random(int count, char[] chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, 0, chars.length, false, false, chars, RANDOM);
    }
    
}