java – 从double转换为int并不总是只是放弃小数部分

public class MeaningOfLife {
  public static String findOutWhatLifeIsAllAbout() {
  int meaning = 0;
  for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 20; j++) {
      for (int k = 0; k < 300; k++) {
        for (int m = 0; m < 7000; m++) {
          meaning += Math.random() + 1;
        }
      }
    }
  }
  return String.valueOf(meaning).replaceAll("0*$","");
  }

public static void main(String[] args) {
  System.out.println(findOutWhatLifeIsAllAbout());
}
}

问题“打印什么”的答案似乎很明显,一旦我意识到有一个隐含的演员与compound assignment operator =.

但是它打印出如：420000006或420000007,
而不是(预期)420000000(或“42”,删除尾随零).

所以这表明从double到int的转换不总是只是放弃双倍的小数部分,如这里所述：How to cast a double to an int in Java?

所以我做了一些试验,这里是我发现的一个例子：

System.out.println((int)  (131070.99999999999)); // -> 131070
System.out.println((int)  (131071.99999999999)); // -> 131071
System.out.println((int)  (131072.99999999999)); // -> 131073 !!!
System.out.println((int)  (131073.99999999999)); // -> 131074 !!!


System.out.println((int)  (16382.999999999999)); // -> 16382
System.out.println((int)  (16383.999999999999)); // -> 16383
System.out.println((int)  (16384.999999999999)); // -> 16385 !!!
System.out.println((int)  (16385.999999999999)); // -> 16386 !!!

那么现在我正在寻找一个解释这个行为？