You use this library to generate a random number and insert the number into an array variable index. You can add one or several random numbers into your array variables, but Java does not ...

java.lang.IndexOutOfBoundsException: String array index number (3) must not be greater than size (2) at com.google.common.base.Preconditions. checkPositionIndex (Preconditions. java: 351) ...

In Java, some array types are covariant and/or contravariant. In the case of covariance, this means that if T is compatible to U, then T[] is also compatible to U[].