java随机数

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，分别是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。
           如果2个Random对象使用相同的种子（比如都是100），并且以相同的顺序调用相同的函数，那它们返回值完全相同。如下面代码中两个Random对象的输出完全相同
          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重复随机数
            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]);
                  }
               }
            }