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()); 
                } 
        } 
}