Why must a final variable be initialized before constructor completes?

Question

Why must a final variable be initialized before constructor completes?

public class Ex
{
  final int q;
}

When I compile this code I get er

Answer 1

The value of a final variable can only be set once. The constructor is the only place in the code for a class that you can guarantee this will hold true; the constructor is only ever called once for an object but other methods can be called any number of times.