Java Class Cache Problem

I found this cache problem during my development. Example of how this problem can be happen:

If these two java files compiled into class files previously, then we might need to be careful when changing the "planId" constants value. The problem happen when we change the "planId" value to some other value & only compile the Constants.java file. In this case, Main.class file still refer to previous "planId" value which is "999".

So, the best solution is to remove all the classes & compile all java files again which we called it as Clean Build.