Q1: why we should initialize final field before completion of new instance?
final means no changeable in java enviroment, the java compiler urges us follow the security violation.
Q2: how to resolve the error above?
actually, it is because factors perhaps refer to passed parameter.
so , keeping a good habit to add the prefix ‘this.‘ is good manner to resolve the error.
this.factors = Arrays.copyof....
the blank final field factors may not have been initialized
原文：https://www.cnblogs.com/daniel123/p/9066487.html