一个java精度问题1/5 与 (double)1/5 区别

for (int i = 0; i < 1000; i++) {
  double randow = Math.random();
  System.out.println(randow);
  System.out.println((double)1/5);
  if(randow<((double)1/5)){
    System.out.println("true");
  }
}

System.out.println(1/5);  == 0
System.out.println((double)1/5); == 0.2