a Grid Computing System - Utopia

}
3. The Basic Building Block - ONTA (Object Network Transfer Architecture)
A ca; B db;
D cd; ....
.... }
Figure 3.2.: Example of an object’s references hierarchy
The hierarchy of references created by this object being saved to the jar archive is presented
in figure 3.2. Starting with the object that instantiated the class A, we should traverse all the
references and save the class B and class D. We are stressing here that the references are all resolved
at compile time by Java, even the ones referring to an interface implementation (e.g. interf1 Obj
= new Implementation()) and hence all the classes needed for an object can be found by starting
at analyzing the class file for the class that that object is an implementation of. Than we should
check all the references in those classes too. Checking the references in class B we end up saving
the class C and then, checking the references of this class, we could end up in a loop. This should
be avoided. At a first look, it looks like we should avoid to begin inspecting the objects, not the
classes that have been previously traversed. That is because there could be other instances of the
same class that could lead to different points in the hierarchy. That is not true, since different
instances of the same class will end up leading us to the same classes, hence this is a static traverse
of the class hierarchy graph. Even if there are multiple instances of the same class in the hierarchy,
we should only begin to traverse the first instance encountered.
The implementation does an iterative deep-first traverse of the graph, keeping track of nodes
in a stack that remembers all the classes that were already saved. Actually, if we think about the
fact that we are not going on with traversing any node that has been previously inspected, we end
up concluding that the structure could be thought of as a tree, so we are doing a iterative depth-
first traverse of a general tree. Since the algorithm of doing this is common, we would not get
any further into details about the implementation. We are first saving the classes that are referred
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