Question

While the object is being constructed, can it be null ?

class Sample {
  public Sample() {
      if( this != null ) { // Is this check necessary anywhere in the constructor?
        this.doSomething();
      }
  }
 ....
 ....
}

Answer 1

this won’t be null – but if you call a non-final instance method from a constructor, you should document that really thoroughly, as any subclass constructors won’t have been run yet. That means if doSomething() is overridden in a subclass, it will see the default values for any fields declared in that subclass (where the default is the default value for the type, not whatever the variable initializer might show). Basically it’s worth trying to avoid calling non-final instance methods in constructors if at all possible.