I'm trying to give a set an attribute that is a vector, and that is in a y class, however I'm having a x class, which is made up of this y class.
At the time I write the code does not give any error, however when I run the following error I get:
error: Exception in thread "main" java.lang.NullPointerException at Request.readMasses (Request.java:80)
How can I resolve this?
Class y: 
Classx: 
The error:
Exception in thread "main" java.lang.NullPointerException at Request.readMasses (Request.java:80)
means that you are trying to do some operation on an object that is null! I usually say that it is the simplest error to be corrected in java, because it directs us to exactly that object! ;)
For your code, your " massas " object at line 80 of the "Order" class (Class X) is null and you are trying to add a description to it.
Since I could not test your code, I can just give you the hint of initializing your object before setting attributes on it.
A simple Massas massas = new Massas(); before line 80 would solve your problem.
