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In java, can a contructor in a class call an overloaded constructor of its superclass (say if we wanted to make that call explicitly and deliberately). I know that a constructor in a class makes implicit call to no-arg default constructor of superclass ( with super (); ) . but suppose I make a call to an overloaded superclass constructor (say super(String s); ) , then my question is, Is this possible? And if this is possible, then is a call to super() still made ahead of super(String s)or not and what are its implications? Also can two constructors from same class one no-arg and one overloaded call each other? Will they be caught in a loop if they do so?

user2029261
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1 Answers1

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You can get the answer in its official tutorial: https://docs.oracle.com/javase/tutorial/java/IandI/super.html

Read this specifically:

The syntax for calling a superclass constructor is

    super();

or: 

    super(parameter list);

With super(), the superclass no-argument constructor is called. With super(parameter list), the superclass constructor with a matching parameter list is called.

Note: If a constructor does not explicitly invoke a superclass constructor, the Java compiler automatically inserts a call to the no-argument constructor of the superclass. If the super class does not have a no-argument constructor, you will get a compile-time error. Object does have such a constructor, so if Object is the only superclass, there is no problem. If a subclass constructor invokes a constructor of its superclass, either explicitly or implicitly, you might think that there will be a whole chain of constructors called, all the way back to the constructor of Object. In fact, this is the case. It is called constructor chaining, and you need to be aware of it when there is a long line of class descent.

So to answer your question: Yes, it is possible, and doable. When you explicitly invoke super constructor with arguments, then only that constructor is invoked.

And, make sure the super constructor invocation is the first line in your constructor, otherwise a compiler error will show.

*****EDITED*****

And, you invoke one specific super class constructor, implicitly or explicit, only. When that superclass constructor is called no other superclass constructors are called, unless it is called within your called superclass constructor. Meanwhile, it is not possible to compile if in the same class multiple constructors call each other recursively - it will be rejected by your compiler.

Hope this helps.

Bruce
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  • I got relevant comment here: http://stackoverflow.com/questions/285177/how-do-i-call-one-constructor-from-another-in-java Note that you can only chain to one constructor, and it has to be the first statement in your constructor body. Just wanted to confirm that will we be caught in a loop if we call constructors from within each other as mentioned in this post. – user2029261 Jan 30 '16 at 07:28
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    There cannot possibly be. Subclass's constructor can call this() or super() at its first line, but superclass's constructor can only call its own (this), but its subclass's constructor. Therefore no loop is possible in your scenario. – Bruce Jan 30 '16 at 07:38
  • Bruce i was suggesting a possibility of 2 constructors in same class (one no-arg and one overloaded) calling each other using - this keyword in their body, as is attempted in before mentioned url. – user2029261 Jan 30 '16 at 08:03
  • I got your point. Such kind of loop in the same class is checkable by compiler and it won't compile. In that case you will encounter a compiler error: "recursive constructor invocation". – Bruce Jan 30 '16 at 08:20
  • In your original post you said super class constructor super(...), but never asked anything about constructors calling each other in the same class. If that is what you intended to ask you should consider revise your original post. – Bruce Jan 31 '16 at 04:23