Program comprehension is a vital mental process in any maintenance activity. It becomes decisive as functions get larger. Such functions are burdened with very many programming constructs as lines of code (LOC) strongly correlate with the McCabe's cyclomatic complexity (MCC). This makes it hard to capture the whole code of such functions and as a result hinders grasping their structural properties that might be essential for maintenance. Program visualization is known as a key solution that assists in comprehending complex systems. As a matter of fact we have shown, in a recent work, that control structure diagrams (CSD) could be useful to better understand and discover structural properties of such functions. For example, we found that the code regularity property, and even cloning, can be easily identified by CSDs. This paper presents JCSD, which is an Eclipse plug-in that implements CSD diagrams for Java methods. In particular it visualizes the control structure and nesting of a Java method, and by this it easily conveys structural characteristics of the code to the programmer and helps him to better understand and refactor.