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

If an instance variable is declared with final keyword, it means it can not be modified later, which makes it a constant. That is why we have to initialize the variable with final keyword.Initialization must be done explicitly because JVM doesnt provide default value to final instance variable.Final instance variable must be initialized either at the time of declaration like:

class Test{
   final int num = 10;
   }

or it must be declared inside an instance block like:

class Test{
 final int x;
  {
   x=10;
  }
} 

or it must be declared BEFORE constructor COMPLETION like:

class Test{
 final int x;
  Test(){ 
   x=10;
  }
}

Keep in mind that we can initialize it inside a consructor block because initialization must be done before constructor completion.