(discuss) classes loaded by two different class loaders cannot be cast to one another

[Pho Tek]

I've accepted this statement for so many years but have never asked why it is the case. When two classloaders load the same binary bits of a class (e.g. Foo for discussion sake) from the filesystem, are the two original "bit representations" of Foo decorated with information of the classloader that loaded it ?

[Ernest Friedman-Hill]

More or less, yes. Loading a class creates a Class object; that Class knows which loader loaded it. A given ClassLoader will load only one class by a given name. The VM Spec talks about class identity being determined by a (name, ClassLoader) pair; the Class object provides that association.

Each object has a reference to its Class object, and two objects loaded by different loaders can belong to classes with identical names, but distinct Class objects; in this case the two objects are said to belong to different classes.

[Pho Tek]

I would like to ask another question on classloading.

Imagine I have a service class that looks like this:

    
class ISecurityService
{
    Person findAllEmployees();
}

In order to call the findAllEmployees method, I would need these classes loaded:

ISecurityService

SecurityServiceImpl

Do I need class Person to be loaded as well ?

And if Person class has a Address field, do we need to load Address as well ?

Thanks.

[Ilja Preuss]

Originally posted by Pho Tek:
I would like to ask another question on classloading.

You will have a bigger chance of getting good answers by asking it in a new thread, with a matching subject line.