随机数测试

  学习链接 http://lavasoft.blog.51cto.com/62575/113758/


import java.util.Random; /** 
* 随机数、随即字符串工具 
* 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"; /** * 返回一个定长的随机字符串(只包含大小写字母、数字) * * @param length 随机字符串长度 * @return 随机字符串 */ 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(); } /** * 返回一个定长的随机纯字母字符串(只包含大小写字母) * * @param length 随机字符串长度 * @return 随机字符串 */ 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(); } /** * 返回一个定长的随机纯大写字母字符串(只包含大小写字母) * * @param length 随机字符串长度 * @return 随机字符串 */ public static String generateLowerString(int length) { return generateMixString(length).toLowerCase(); } /** * 返回一个定长的随机纯小写字母字符串(只包含大小写字母) * * @param length 随机字符串长度 * @return 随机字符串 */ public static String generateUpperString(int length) { return generateMixString(length).toUpperCase(); } /** * 生成一个定长的纯0字符串 * * @param length 字符串长度 * @return 纯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(); } /** * 根据数字生成一个定长的字符串，长度不够前面补0 * * @param num             数字 * @param fixdlenth 字符串长度 * @return 定长的字符串 */ 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("将数字" + num + "转化为长度为" + fixdlenth + "的字符串发生异常！"); } sb.append(strNum); return sb.toString(); } /** * 根据数字生成一个定长的字符串，长度不够前面补0 * * @param num             数字 * @param fixdlenth 字符串长度 * @return 定长的字符串 */ 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("将数字" + num + "转化为长度为" + fixdlenth + "的字符串发生异常！"); } 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)); } 
}

　　小的随机数实验：

 

import java.util.Random; /** 
* Java随机数测试 
* 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()--------------"); //返回以毫秒为单位的当前时间。 long r1 = System.currentTimeMillis(); //返回带正号的 double 值，大于或等于 0.0，小于 1.0。 double r2 = Math.random(); //通过Random类来获取下一个随机的整数 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()--------------"); //创建不带种子的测试Random对象 Random random = new Random(); for (int i = 0; i < 3; i++) { System.out.println(random.nextInt()); } } public static void testSeed1() { System.out.println("--------------testSeed1()--------------"); //创建带种子的测试Random对象 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()--------------"); //创建带种子的测试Random对象 Random random = new Random(); random.setSeed(555L); for (int i = 0; i < 3; i++) { System.out.println(random.nextInt()); } } 
}