The paper describes the experience gained in the development of Java applications in a nuclear fusion experiment. Two Java tools for graphical data display and experiment configuration set-up are presented as case studies. Based on these tools, the results derived by the application of some metrics for object oriented software and by the analysis of the design patterns imported in the applications are presented to highlight the effective code reuse achieved with Java. The main issues in the applicability of Java in a demanding environment are then introduced and a few weaknesses of the language are finally discussed. Copyright © 2001 John Wiley & Sons, Ltd.