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

Both of the methods are acceptable. Note that in the latter case b=new B() may not get initialized if there is another constructor present. Think of initializer code outside constructor as a common constructor and the code is executed.