在Java中我们能够使用java.util.Random类来产生一个随机数发生器。它有两种形式的构造函数，各自是Random()和Random(long seed)。Random()使用当前时间即System.currentTimeMillis()作为发生器的种子，Random(long seed)使用指定的seed作为发生器的种子。

         随机数发生器(Random)对象产生以后，通过调用不同的method：nextInt()、nextLong()、nextFloat()、nextDouble()等获得不同类型随机数。

        1>生成随机数
            Random random = new Random();
            Random random = new Random(100);//指定种子数100
            random调用不同的方法，获得随机数。
            假设2个Random对象使用同样的种子（比方都是100），而且以同样的顺序调用同样的函数，那它们返回值全然同样。如以下代码中两个Random对象的输出全然同样
           import java.util.*;
           class TestRandom {
                 public static void main(String[] args) {
                      Random random1 = new Random(100);
                      System.out.println(random1.nextInt());
                      System.out.println(random1.nextFloat());
                      System.out.println(random1.nextBoolean());
                      Random random2 = new Random(100);
                      System.out.println(random2.nextInt());
                      System.out.println(random2.nextFloat());
                      System.out.println(random2.nextBoolean());
                 }
             }

         2>指定范围内的随机数
              随机数控制在某个范围内,使用模数运算符%
             import java.util.*;
                  class TestRandom {
                       public static void main(String[] args) {
                            Random random = new Random();
                            for(int i = 0; i < 10;i++) {
                                System.out.println(Math.abs(random.nextInt())%10);
                            }
                       }
                  }
              获得的随机数有正有负的，用Math.abs使获取数据范围为非负数

        3>获取指定范围内的不反复随机数
             import java.util.*;
             class TestRandom {
                   public static void main(String[] args) {
                        int[] intRet = new int[6];
                        int intRd = 0; //存放随机数
                        int count = 0; //记录生成的随机数个数
                        int flag = 0; //是否已经生成过标志
                        while(count<6){
                             Random rdm = new Random(System.currentTimeMillis());
                             intRd = Math.abs(rdm.nextInt())%32+1;
                             for(int i=0;i<count;i++){
                                 if(intRet[i]==intRd){
                                     flag = 1;
                                     break;
                                 }else{
                                     flag = 0;
                                 }
                             }
                             if(flag==0){
                                 intRet[count] = intRd;
                                 count++;
                             }
                    }
                   for(int t=0;t<6;t++){
                       System.out.println(t+"->"+intRet[t]);
                   }
                }
             }