CODEWITHSUNDEEP
javainheritanceconstructorsuperclasssuper
The Hairy Lemon
The Hairy Lemon

Reputation: 97

What is invoking the super class constructor here?

I came across this code while looking for exam prep questions. I don't understand what is invoking the superclass constructor in this code?

The output is ---> feline cougar cc

THL

        public class Feline{

        public String type = "f ";

        public Feline(){
            System.out.print("feline ");
        }
        }

-

    public class Cougar extends Feline {

    public Cougar(){
            System.out.print("cougar ");
    }

    public static void main(String[] args){
            new Cougar().go();                    
    }                                                                                     
    void go(){                            
            type = "c ";                                
            System.out.print(this.type + super.type);
    }
    }

Upvotes: 0

Views: 70

Answers (3)

Mshnik
Mshnik

Reputation: 7032

When you have a class that extends some other class, eg Cougar extends Feline, there must be a call to the super class at the top of the constructor. When you don't write one, Java assumes you meant to call the default super class constructor. So your constructor:

public Cougar(){
    System.out.print("cougar ");
}

Is actually interpreted as:

public Cougar(){
     super();
     System.out.print("cougar ");
}

Hence the call to the super class constructor. It's interesting to note that because all classes are extensions of the class Object, there is a call to a super class constructor at the beginning of every constructor that you'll ever write - either an explicit one you've included with or without arguments, or the default super class constructor if you do not specify.

Upvotes: 3

telkins
telkins

Reputation: 10540

The Java compiler will automatically insert a call to super() in this case. I'd suggest reading over this Java tutorial, specifically this part:

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.

Upvotes: 1

Damian Nikodem
Damian Nikodem

Reputation: 1289

If you do not include a call to the parents constructor then the parents( no arg ) constructor will get called before the first line of execution in the current class

Upvotes: 0

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