If the class that defines the application is defined in a package, you need to include the package path just as when running the application under the JVM software, as in the following example.
(dbx) debug java.pkg.Toy.class
You can debug a file that uses the .class file name extension using dbx.You can also use a full path name for the class file. dbx automatically determines the package portion of the class path by looking in the .class file and adds the remaining portion of the full path name to the class path. For example, given the following path name, dbx determines that pkg/Toy.class is the main class name and adds /home/user/java to the class path.
(dbx) debug /home/user/java/pkg/Toy.class