This paper introduces an automated grader for Java programs called GUI_Grader that allows students a degree of flexibility in graphical user interface (GUI) design. GUI_Grader allows students to build multiwindow Java applications, choose among alternative GUI components, and decide how to order, position and label components. This enables students to practice some aspects of designing their own GUI applications while still providing automated grading `based on a single test plan. The data-driven approach helps to maintain consistency between test plans and program specifications. Testing GUI_Grader on Java assignments from both a first-year and an upper-year course confirms the feasibility of the approach.