Generics problem

[Ronwaldo Cruz]

Hi, I have written a piece of code show below:

   

    public interface Dog
    {
        public <T extends Person> T getOwner();
        public <T extends Person> void setOwner(T owner);
        
    }
    
    public class ConcreteDog implements Dog
    {
        private Hunter owner;

        public Hunter getOwner() {
            return owner;
        }

        public void setOwner(Hunter owner) {
            this.owner = owner;
        }
        
    }
    
    public interface Person
    {
        
    }
    
    public interface Hunter extends Person
    {
        
    }

 

The problem is that the interface method Dog.getOwner seems to have been successfully "implemented" by ConcreteDog.getHunter. However, Dog.setOwner doesn't seem to recognize ConcreteDog.setHunter as a suitable implementation. The 2 looks the same to me. Can somebody please help?

[subodh gupta]

Hi,

You cannot use extends in both the get and put logic you should use extends for getting and super for putting a variable of a type.

[Rob Spoor]

It seems to me that you want to connect the Person type in both getOwner and setOwner. Changing the T to a class generic type could solve this:

interface Dog<T extends Person>
{
    public T getOwner();
    public void setOwner(T owner);
}

class ConcreteDog implements Dog<Hunter>
{
    private Hunter owner;

    public Hunter getOwner() {
        return owner;
    }

    public void setOwner(Hunter owner) {
        this.owner = owner;
    }
}

interface Person
{
}

interface Hunter extends Person
{
}

[Ronwaldo Cruz]

This helped. Thanks