Should I instantiate instance variables on declaration or in the constructor?

Question

Is there any advantage for either approach?

Example 1:

class A {
    B b = new B();
}

Example 2:

class A {
    B b;         


        

Answer 1

It's quite different actually:

The declaration happens before construction. So say if one has initialized the variable (b in this case) at both the places, the constructor's initialization will replace the one done at the class level.

So declare variables at the class level, initialize them in the constructor.