I am doing a project , I need produce a product to "watch" the changing of variable of program in sound, this way may assist novice programmer to debug. They can not only use eyes to watch the variable on Screen, but also can hear the changing of variable. it is obviously to reduce the workload of programmer. I have produced two java classes. One is the class can play MIDI notes, another is quite easy that watch the changing of variable, but need a sentence insert into the target java source file, after the changing of the variable. for instance, in a bubble sort program, if I intend to watch the variable n(from 0 to 10), I must insert manually a watching sentence where the line after the n changes line. But I need let a program automaticly parse the target java file, and automaticly insert the watching sentence into the right place.