ADomainCombiner is passed as a parameter to the appropriate constructor forAccessControlContext. The newly constructed context is then passed to theAccessController.doPrivileged(..., context) method to bind the provided context (and associatedDomainCombiner) with the current execution thread. Subsequent calls toAccessController.getContext orAccessController.checkPermission cause theDomainCombiner.combine to get invoked.

The combine method takes two arguments. The first argument represents an array of ProtectionDomains from the current execution thread, since the most recent call toAccessController.doPrivileged. If no call to doPrivileged was made, then the first argument will contain all the ProtectionDomains from the current execution thread. The second argument represents an array of inherited ProtectionDomains, which may benull. ProtectionDomains may be inherited from a parent thread, or from a privileged context. If no call to doPrivileged was made, then the second argument will contain the ProtectionDomains inherited from the parent thread. If one or more calls to doPrivileged were made, and the most recent call was to doPrivileged(action, context), then the second argument will contain the ProtectionDomains from the privileged context. If the most recent call was to doPrivileged(action), then there is no privileged context, and the second argument will benull.

Thecombine method investigates the two input arrays of ProtectionDomains and returns a single array containing the updated ProtectionDomains. In the simplest case, thecombine method merges the two stacks into one. In more complex cases, thecombine method returns a modified stack of ProtectionDomains. The modification may have added new ProtectionDomains, removed certain ProtectionDomains, or simply updated existing ProtectionDomains. Re-ordering and other optimizations to the ProtectionDomains are also permitted. Typically thecombine method bases its updates on the information encapsulated in theDomainCombiner.

After theAccessController.getContext method receives the combined stack of ProtectionDomains back from theDomainCombiner, it returns a new AccessControlContext that has both the combined ProtectionDomains as well as theDomainCombiner.