kb QUESTION PG 617

[Dinesh Tahiliani]

public class Group extends HashSet<Person>
{
 
public static void main(String a[])
{
Group g = new Group();
g.add(new Person("Ami"));
g.add(new Person("Ridzz"));
g.add(new Person("Din"));
System.out.println(g.size() :wink: 
 
}
 
public boolean add(Object o)
{
return super.add(o);
}
}
 
class Person
{
private final String name;
public Person(String nm)
{
name = nm;
}
public String toString()
{
return name;
}
}

The above code doesn't complie and gives error . can't add person
Please advise and correct if any code added in code.

[Matt Russell]

Because you're extending a generic version of HashSet, you need to override the add method with a Person argument, not an Object, like this:

  public boolean add(Person o) {...

[Dinesh Tahiliani]

So i need to correct my add method

public boolean add(Person o)
{
return super.o;
}

Could please teel wht super.o will do..

Correct me if i am wrong

[Matt Russell]

You need super.add(o), rather than super.o. That will call the implementation of add() in HashSet, the superclass of Group, and will add the person to the HashSet. There's not much point to the override, as the HashSet add() method would have been called in any case.

[Ninad Kulkarni]

name clash: add(java.lang.Object) in Group and add(E) in java.util.HashSet<Person> have the same erasure, yet neither overrides the other
public class Group extends HashSet<Person> {
^

I got above error while compiling please explain it

I keep signature of the method public boolean add(Object o)as it is
while compiling

[Bert Bates]

Hey Dinesh,

It would be good to understand what part of the question's answer was confusing?

Thanks,

Bert

[Madhukar Ojha]

Signature of your add method must be like this .

public boolean add(Person o)
{
return super.add(o);
}

Because HashSet is instantiated with type parameter Person .
Hence add method of HashSet class will take Person object only .