Please anyone explain me the working of below proram

[pradeep singh]

Hi
Please anyone explain me the working of below proram.How it works?

Both class have two constructors and we have not make a call to super constructot having argument in the sub-class constructor explicitly even super class has a constructor with arguments.Why?

class boo
{
boo(String s){}
boo(){}


}


class bar extends boo
{ static String s;
bar(){}
bar(String s)
{
// super(s);

}


public static void main(String...args)
{
bar b=new bar(s);
}

}

[Burkhard Hassel]

I'm not sure if I got your question right.
Why we are not forced to put in the line that you have commented out?

Because then the call for the parameterless constructor will be made automatically. Because it must be sure that at least one constructor of the super class will be called.
Without the call super(s), super() will be called.

Yours,
Bu.

[Akshay Dashrath]

Hey all,

This is my first post ,

I'm a complete beginner, just finished my BE in mech and studying Java to write SCJP, so guys please go easy on me .

Regarding the above question, if we dont call super(s) would'nt the default constructor of super be called due to super()? If so then an instance of the superclass cannot be called(here its "s") is that right?

Thanks,

Akshay

[Burkhard Hassel]

Howdy Akshay,

welcome to the ranch!




yes you are right. Without "manually" providing a call to any of the constructors of the super class, the parameterless constructor would be called with super().
Running it with parameter s is ok, because the subclass has this variable and it hands it over to the superclass via this reference (that it is null does not matter here):

class Boo {
Boo() {
System.out.println("Boo parameterless");
}
Boo(String s) {
System.out.println("Boo, String: " + s);
}
}
 
class Bar extends Boo {
 
static String s;
 
Bar() {
System.out.println("Bar parameterless");
}

Bar(String s){
// super(s);
}

public static void main(String[] args){
Bar b = new Bar(s);
}
}

As it is it prints:
Boo parameterless

If you remove the // then it prints:
Boo, String: null



Yours,
Bu.

[Deepak Jain]

Welcome Akshay This is the friendliest java forum in the entire universe

bar b=new bar(s);
This invokes the String constructor of bar class. bar(String s) {// super(s);}
Note: Every child class constructor must explicitly or implicitly invoke the parent class constructor. In the child class bar(String s) {} will implicitly have a call to super() or you can explicitly call class bar(String s) { super();} In this case there must be a boo(){} defined in parent class or class bar(String s) { super(s);} in this case there must be boo(String s) {} defined in boo class.
Note when you define a parameter constructor in your class Java compiler will not place its default no argument constructor, its your job to define to explicitly as explained above.
Hope this clears

[Akshay Dashrath]

Thank you Burkhard and Deepak. Tried it out on the comp too. Thanks again.

Regards,

Akshay

[pradeep singh]

Hi
Thanks to you all .i am well understood now.