A diagnostic system in an aspect-oriented data processing environment is provided. The environment comprises a data processing system having an operating system for executing an application, wherein the application comprises an object class. The environment also comprises means for loading the object class at runtime and storage means for storing a diagnostic aspect. An aspect implements concerns (e.g. logging, security) that cross-cut the application. The object class of the application is loaded at runtime and the diagnostic aspect is read from the storage means. The means for loading now combines the object class with the diagnostic aspect, so that for example, diagnostics can be captured and repairs on the application can be carried out.