Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.lang3; import java.util.Random; /** * <p>Operations for random {@code String}s.</p> * <p>Currently <em>private high surrogate</em> characters are ignored. * These are Unicode characters that fall between the values 56192 (db80) * and 56319 (dbff) as we don't know how to handle them. * High and low surrogates are correctly dealt with - that is if a * high surrogate is randomly chosen, 55296 (d800) to 56191 (db7f) * then it is followed by a low surrogate. If a low surrogate is chosen, * 56320 (dc00) to 57343 (dfff) then it is placed after a randomly * chosen high surrogate. </p> * * <p>#ThreadSafe#</p> * @since 1.0 * @version $Id$ */ 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} instances should NOT be constructed in * standard programming. Instead, the class should be used as * {@code RandomStringUtils.random(5);}.</p> * * <p>This constructor is public to permit tools that require a JavaBean instance * to operate.</p> */ public RandomStringUtils() { super(); } // 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(final 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} and {@code 126} (inclusive).</p> * * @param count the length of random string to create * @return the random string */ public static String randomAscii(final 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(final 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(final 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(final 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}, generated string may include * alphabetic characters * @param numbers if {@code true}, generated string may include * numeric characters * @return the random string */ public static String random(final int count, final boolean letters, final 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}, generated string may include * alphabetic characters * @param numbers if {@code true}, generated string may include * numeric characters * @return the random string */ public static String random(final int count, final int start, final int end, final boolean letters, final 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}, then it will use the set of all chars. * @return the random string * @throws ArrayIndexOutOfBoundsException if there are not * {@code (end - start) + 1} characters in the set array. */ public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers, final 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}, start and end are set * to {@code ' '} and {@code 'z'}, the ASCII printable * characters, will be used, unless letters and numbers are both * {@code false}, in which case, start and end are set to * {@code 0} and {@code Integer.MAX_VALUE}. * * <p>If set is not {@code null}, 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, must not be empty. * If {@code null}, 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} characters in the set array. * @throws IllegalArgumentException if {@code count} < 0 or the provided chars array is empty. * @since 2.0 */ public static String random(int count, int start, int end, final boolean letters, final boolean numbers, final char[] chars, final Random random) { if (count == 0) { return ""; } else if (count < 0) { throw new IllegalArgumentException("Requested random string length " + count + " is less than 0."); } if (chars != null && chars.length == 0) { throw new IllegalArgumentException("The chars array must not be empty"); } if (start == 0 && end == 0) { if (chars != null) { end = chars.length; } else { if (!letters && !numbers) { end = Integer.MAX_VALUE; } else { end = 'z' + 1; start = ' '; } } } else { if (end <= start) { throw new IllegalArgumentException( "Parameter end (" + end + ") must be greater than start (" + start + ")"); } } final char[] buffer = new char[count]; final 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 && Character.isLetter(ch) || numbers && Character.isDigit(ch) || !letters && !numbers) { if (ch >= 56320 && ch <= 57343) { if (count == 0) { count++; } else { // low surrogate, insert high surrogate after putting it in buffer[count] = ch; count--; buffer[count] = (char) (55296 + random.nextInt(128)); } } else if (ch >= 55296 && ch <= 56191) { if (count == 0) { count++; } else { // high surrogate, insert low surrogate before putting it in buffer[count] = (char) (56320 + random.nextInt(128)); count--; buffer[count] = ch; } } else if (ch >= 56192 && ch <= 56319) { // private high surrogate, no effing clue, so skip it count++; } else { buffer[count] = ch; } } else { count++; } } return new String(buffer); } /** * <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 by the string, must not be empty. * If null, the set of all characters is used.</p> * * @param count the length of random string to create * @param chars the String containing the set of characters to use, * may be null, but must not be empty * @return the random string * @throws IllegalArgumentException if {@code count} < 0 or the string is empty. */ public static String random(final int count, final 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} < 0. */ public static String random(final int count, final char... chars) { if (chars == null) { return random(count, 0, 0, false, false, null, RANDOM); } return random(count, 0, chars.length, false, false, chars, RANDOM); } }