AguiaJ is an pedagogical environment for experimenting object-oriented programming in Java. The tool enables users to interactively test object classes by creating and manipulating objects and visualizing the result of such interaction in terms of object state. The notion of encapsulation is metaphorically embodied in the environment, by restricting visibility/access to class/package members. Another innovative aspect of the tool is the capability of being extended with model-view plugins that enable users to visualize certain objects with custom views, enriching user experience and enabling introductory programming exercises to deal only with objects as conceptual descriptions of artifacts that are visualized in the tool.