A computer system includes multiple class loaders for loading program class
files into the system. A constraint checking mechanism is provided wherein
a first class file loaded by a first class loader makes a symbolic
reference to a second class file loaded by a second class loader, the
symbolic reference including a descriptor of a third class file. The
constraint mechanism requires that the first and second class files agree
on the identity of the third class file and stores a list of constraints
as a set of asymmetric relationships between class loaders. Each stored
constraint, for a class loader which loaded a class file that contains a
symbolic reference to another class file, includes a first parameter
denoting the class loader which loaded the class file to which the
symbolic references is made; and a second parameter denoting a class file
which is identified by a descriptor in said symbolic reference.
