001    /**
002     * Copyright (c) 2000-2013 Liferay, Inc. All rights reserved.
003     *
004     * This library is free software; you can redistribute it and/or modify it under
005     * the terms of the GNU Lesser General Public License as published by the Free
006     * Software Foundation; either version 2.1 of the License, or (at your option)
007     * any later version.
008     *
009     * This library is distributed in the hope that it will be useful, but WITHOUT
010     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
011     * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
012     * details.
013     */
014    
015    package com.liferay.portal.kernel.security;
016    
017    import java.util.Random;
018    
019    /**
020     * @author Shuyang Zhou
021     */
022    public class RandomUtil {
023    
024            public static int nextInt(int n) {
025                    return random.nextInt(n);
026            }
027    
028            public static int[] nextInts(int n, int size) {
029                    if (size > n) {
030                            size = n;
031                    }
032    
033                    int[] numbers = new int[n];
034    
035                    for (int i = 0; i < n; i++) {
036                            numbers[i] = i;
037                    }
038    
039                    shuffle(random, numbers);
040    
041                    if (size == n) {
042                            return numbers;
043                    }
044    
045                    int[] results = new int[size];
046    
047                    System.arraycopy(numbers, 0, results, 0, size);
048    
049                    return results;
050            }
051    
052            public static void shuffle(Random random, int[] numbers) {
053                    for (int i = numbers.length; i > 1; i--) {
054                            int position = random.nextInt(i);
055    
056                            if (position != (i - 1)) {
057                                    int number = numbers[position];
058    
059                                    numbers[position] = numbers[i - 1];
060                                    numbers[i - 1] = number;
061                            }
062                    }
063            }
064    
065            public static String shuffle(Random random, String s) {
066                    StringBuilder sb = new StringBuilder(s);
067    
068                    shuffle(random, sb);
069    
070                    return sb.toString();
071            }
072    
073            public static void shuffle(Random random, StringBuilder sb) {
074                    for (int i = sb.length(); i > 1; i--) {
075                            int position = random.nextInt(i);
076    
077                            if (position != (i - 1)) {
078                                    char c = sb.charAt(position);
079    
080                                    sb.setCharAt(position, sb.charAt(i - 1));
081                                    sb.setCharAt(i - 1, c);
082                            }
083                    }
084            }
085    
086            public static String shuffle(String s) {
087                    return shuffle(random, s);
088            }
089    
090            protected static Random random = new Random();
091    
092    }