學習鏈接 http://lavasoft.blog.51cto.com/62575/113758/


import java.util.Random; /** * 隨機數(shù)、隨即字符串工具 * User: leizhimin * Date: 2008-11-19 9:43:09 */ public class RandomUtils { public static final String allChar = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; public static final String letterChar = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; public static final String numberChar = "0123456789"; /** * 返回一個定長的隨機字符串(只包含大小寫字母、數(shù)字) * * @param length 隨機字符串長度 * @return 隨機字符串 */ public static String generateString(int length) { StringBuffer sb = new StringBuffer(); Random random = new Random(); for (int i = 0; i < length; i++) { sb.append(allChar.charAt(random.nextInt(allChar.length()))); } return sb.toString(); } /** * 返回一個定長的隨機純字母字符串(只包含大小寫字母) * * @param length 隨機字符串長度 * @return 隨機字符串 */ public static String generateMixString(int length) { StringBuffer sb = new StringBuffer(); Random random = new Random(); for (int i = 0; i < length; i++) { sb.append(allChar.charAt(random.nextInt(letterChar.length()))); } return sb.toString(); } /** * 返回一個定長的隨機純大寫字母字符串(只包含大小寫字母) * * @param length 隨機字符串長度 * @return 隨機字符串 */ public static String generateLowerString(int length) { return generateMixString(length).toLowerCase(); } /** * 返回一個定長的隨機純小寫字母字符串(只包含大小寫字母) * * @param length 隨機字符串長度 * @return 隨機字符串 */ public static String generateUpperString(int length) { return generateMixString(length).toUpperCase(); } /** * 生成一個定長的純0字符串 * * @param length 字符串長度 * @return 純0字符串 */ public static String generateZeroString(int length) { StringBuffer sb = new StringBuffer(); for (int i = 0; i < length; i++) { sb.append('0'); } return sb.toString(); } /** * 根據(jù)數(shù)字生成一個定長的字符串，長度不夠前面補0 * * @param num 數(shù)字 * @param fixdlenth 字符串長度 * @return 定長的字符串 */ public static String toFixdLengthString(long num, int fixdlenth) { StringBuffer sb = new StringBuffer(); String strNum = String.valueOf(num); if (fixdlenth - strNum.length() >= 0) { sb.append(generateZeroString(fixdlenth - strNum.length())); } else { throw new RuntimeException("將數(shù)字" + num + "轉化為長度為" + fixdlenth + "的字符串發(fā)生異常！"); } sb.append(strNum); return sb.toString(); } /** * 根據(jù)數(shù)字生成一個定長的字符串，長度不夠前面補0 * * @param num 數(shù)字 * @param fixdlenth 字符串長度 * @return 定長的字符串 */ public static String toFixdLengthString(int num, int fixdlenth) { StringBuffer sb = new StringBuffer(); String strNum = String.valueOf(num); if (fixdlenth - strNum.length() >= 0) { sb.append(generateZeroString(fixdlenth - strNum.length())); } else { throw new RuntimeException("將數(shù)字" + num + "轉化為長度為" + fixdlenth + "的字符串發(fā)生異常！"); } sb.append(strNum); return sb.toString(); } public static void main(String[] args) { System.out.println(generateString(15)); System.out.println(generateMixString(15)); System.out.println(generateLowerString(15)); System.out.println(generateUpperString(15)); System.out.println(generateZeroString(15)); System.out.println(toFixdLengthString(123, 15)); System.out.println(toFixdLengthString(123L, 15)); } }

　　小的隨機數(shù)實驗：

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import java.util.Random; /** * Java隨機數(shù)測試 * User: leizhimin * Date: 2008-11-19 17:52:50 */ public class TestRandomNum { public static void main(String[] args) { randomTest(); testNoSeed(); testSeed1(); testSeed2(); } public static void randomTest() { System.out.println("--------------test()--------------"); //返回以毫秒為單位的當前時間。 long r1 = System.currentTimeMillis(); //返回帶正號的 double 值，大于或等于 0.0，小于 1.0。 double r2 = Math.random(); //通過Random類來獲取下一個隨機的整數(shù) int r3 = new Random().nextInt(); System.out.println("r1 = " + r1); System.out.println("r3 = " + r2); System.out.println("r2 = " + r3); } public static void testNoSeed() { System.out.println("--------------testNoSeed()--------------"); //創(chuàng)建不帶種子的測試Random對象 Random random = new Random(); for (int i = 0; i < 3; i++) { System.out.println(random.nextInt()); } } public static void testSeed1() { System.out.println("--------------testSeed1()--------------"); //創(chuàng)建帶種子的測試Random對象 Random random = new Random(555L); for (int i = 0; i < 3; i++) { System.out.println(random.nextInt()); } } public static void testSeed2() { System.out.println("--------------testSeed2()--------------"); //創(chuàng)建帶種子的測試Random對象 Random random = new Random(); random.setSeed(555L); for (int i = 0; i < 3; i++) { System.out.println(random.nextInt()); } } }

　　

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轉載于:https://www.cnblogs.com/xiangtianxiayu/p/5734193.html

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