Why does `instanceof` error rather than return `false` when used for 2 incompatible classes?

Question

I\'m reading this:
http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.20.2

They say:

Consider the example program

Answer 1

Because of the inheritance tree. if A inherited from B then you can write A instance of B

Integer i = 3;

System.out.println(i instanceof String); // compile time error

System.out.println(i instanceof Number); // true

System.out.println(i instanceof Object); // true