logical structure/details of a reference variable and object in the memory?

Question

Let's say we have a class:

class Class1
{
   int i = 1;
}

and we have a variable:

Class1 ob1 = new Class1();

• Does a reference itself stored in a variable ob1 store the information that it refers to an object of Class1?
• Does the part of the heap where Class1 is stored store the information that it is of Class1 type?
• How does logically looks like this information? It's a string like application1.Class1 or a reference to some reference types pool?

If you can recommend the source of such information I'll be very grateful for providing it I can't find it in the reference book.

Answer 1

Does a reference itself stored in a variable ob1 store the information that it refers to an object of Class1?

NO. Reference variable ob1 stores only the reference of the object it points to. And the information about that object is already known to the application (or JVM).

Does the part of the heap where Class1 is stored store the information that it is of Class1 type?

NO. The information about class being loaded is stored in method area. As specified in this link
For each type it loads, a Java virtual machine must store the following kinds of information in the method area:

• The fully qualified name of the type
• The fully qualified name of the type's direct superclass (unless the type is an interface or class java.lang.Object, neither of which have a superclass)
• Whether or not the type is a class or an interface
• The type's modifiers ( some subset of` public, abstract, final)
• An ordered list of the fully qualified names of any direct superinterfaces

How does logically looks like this information? It's a string like application1.Class1 or a reference to some reference types pool?

Inside the Java class file and Java virtual machine, type names are always stored as fully qualified names. For example, the fully qualified name of class Object in package java.lang is representated as java/lang/Object. In the method area, fully qualified names can be represented in whatever form and data structures a designer chooses.

Answer 2

Every java object reference knows its class at runtime; this so-called "run-time type information" is used in code like this:

if (obj instanceof class1) {
  // true!
}

You can also access the class of an object through obj.getClass(). This will return class1.class, an object of class Class<class1>. See the Object.getClass method.

(Note that if your class is parameterized, as class1<T>, the type of T will not be stored at runtime, due to "erasure".)

I don't know whether the class information is stored with the pointer or with the data; it's probably implementation-specific in the jvm; but it hardly matters from a practical standpoint. (So either answer 1 or 2, or both, is "yes").

The answer to 3 is that, as far as a java programmer is concerned, the run-time type information is encapsulated in an object of class Class. Under the covers, a JVM may implement this in one way or another.