Difference between Dynamic and Static type assignments in Java

Question

Given the follow class hierarchy what are the dynamic and static types for the following statements?

Class hierarchy:

class Alpha {}         


        

Answer 1

the dynamic and static types for the following statements

Erm, a statement doesn't have a type, at least there is no such notion in the Java Language Specification. The spec does define two different kinds of types: the declared type of variable, field, or parameter, and the runtime class of an object.

As the name indicates, the declared type of a variable, field or parameter is the type you mention in the declaration. For instance, the declaration Foo bar; declares a variable named bar of type Foo.

The runtime class of an object is determined by the class instance or array creation expression used to construct it, and remains the same throughout the lifetime of that object.

So the code:

Integer i = 1;
Number n = i;
Object o = n;

declares 3 variables of types Integer, Number and Object, respectively, all of which refer to a single object with runtime class Integer.