java产生随机数的几种方式

转自http://blog.youkuaiyun.com/anroidfinalbreak/article/details/33728589

五、综合应用

    下面通过最近写的一个随机数工具类来展示用法：

import java.util.Random;

 
public class RandomUtils

     { 
        public static final String allChar = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
        public static final String letterChar = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
        public static final String numberChar = "0123456789";

         
        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(); 
        }

         
        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(); 
       }

         
        public static String generateLowerString(int length)

        { 
                return generateMixString(length).toLowerCase(); 
        }

         
        public static String generateUpperString(int length)

         { 
                return generateMixString(length).toUpperCase(); 
        }

         
        public static String generateZeroString(int length)

           { 
                StringBuffer sb = new StringBuffer(); 
                for (int i = 0; i < length; i++)

                { 
                        sb.append('0'); 
                } 
                return sb.toString(); 
         }

         
        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(); 
             }

         
        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)); 
        } 
}

    运行结果：

vWMBPiNbzfGCpHG 
23hyraHdJkKPwMv 
tigowetbwkm1nde 
BPZ1KNEJPHB115N 
000000000000000 
000000000000123 
000000000000123