Any idea why super() and this() needs to be first statement

Question

Java recommends super() and this() to be the first statement to be used.why this design constraint is imposed?
This imposes one more restriction
where super() and this() cannot be used at the same time?
how this constraint is useful.
for eg:
class A
     A(int a)
     System.out.println("A(int)");
     A(int a,int b)
     System.out.println("A(int,int)");
class B extends A
     B()
          super(1);
          System.out.println("B()");
     B(int i)
          this();
          super(1,1);//compile-error :must be first statement
the above eg may be a bad design,but are the constraints imposed for this purpose?or anything else?

Answer 1

To make sure that the constructor is the first thing that runs, and to make sure >the super instance is completely constructed before we do anything with the >child instance.
Both these go toward having the object be in a consistent, valid state.I accept the point,but considering the code part
B()
   //super(1);
System.out.println("B()");
B(int i)
super(1,1);
this();
}in above super instance will be constructed first followed by this().
but this() cannot be used as second statement???
I feel ,this is because this() in turn calls the super constructor again?to restrict this constraint made?is it something like that?