Java范型中的协变（covariant）、逆变（contravariant）、不变（invariant）和双变（bivariant），由ArrayStoreException引出的思考

今天在翻Core Java的时候，看这样一段话

In Java, arrays of subclass references can be converted to arrays of superclass references without a cast. For example, consider this array of managers:

 

Manager[] managers = new Manager[10];

 

It is legal to convert this array to an Employee[] array:

 

Employee[] staff = managers; // OK

 

Sure, why not, you may think. After all, if managers[i] is a Manager, it is also an Employee. But actually, something surprising is going on. Keep in mind that managers and staff are references to the same array. Now consider the statement

 

staff[0] = new Empl