There exists bugs in the current implementation which introduces duplicate entries in the class-use listing.
The problems stem from:
   a: the sets are not sorted
   b: the Doc comparator is faulty and allows duplicate entries to be inserted, 
   c: faulty logic in eliminating duplicated entries.

For example:
http://docs.oracle.com/javase/8/docs/api/java/lang/class-use/String.html
Process     Runtime.exec(String[] cmdarray, String[] envp)
Executes the specified command and arguments in a separate process with the specified environment.

Process     Runtime.exec(String[] cmdarray, String[] envp)
Executes the specified command and arguments in a separate process with the specified environment.

Process     Runtime.exec(String[] cmdarray, String[] envp, File dir)
Executes the specified command and arguments in a separate process with the specified environment and working directory.

Process     Runtime.exec(String[] cmdarray, String[] envp, File dir)
Executes the specified command and arguments in a separate process with the specified environment and working directory.

Process     Runtime.exec(String command, String[] envp)
Executes the specified string command in a separate process with the specified environment.

Process     Runtime.exec(String command, String[] envp)
Executes the specified string command in a separate process with the specified environment.


There are some tests case to check for duplication however it is difficult to come up with
test case for inclusion.