Interfaces

[Astha Sharma]

Multiple inheritance in not allowed in java. I now the reason, its because it might be a case that two super classes of a subclass may have methods with same name and thus ambiguity arises when these methods are called.
This can happen with interfaces also, but still it is allowed to a class to implement multiple interfaces!!!
My actual problem is in this code-

interface Animal
{
	public void eat();
}
interface Bird
{
	public int eat();
}
class Horse implements Animal, Bird
{
	public void eat()
	{
		System.out.println("in the horse version");
	}
	public int eat()
	{
		return 0;
	}
}
class TestCode
{
	public static void main(String[]args)
	{
		Horse h=new Horse();
		h.eat();
	}
}

ERROR because eat() is defined two times in the class Horse.
now please tell me how to resolve error in this code?

[sachin potu]

Astha Sharma wrote:Multiple inheritance in not allowed in java. I now the reason, its because it might be a case that two super classes of a subclass may have methods with same name and thus ambiguity arises when these methods are called.
This can happen with interfaces also, but still it is allowed to a class to implement multiple interfaces!!!
My actual problem is in this code-

interface Animal
{
	public void eat();
}
interface Bird
{
	public int eat();
}
class Horse implements Animal, Bird
{
	public void eat()
	{
		System.out.println("in the horse version");
	}
	public int eat()
	{
		return 0;
	}
}
class TestCode
{
	public static void main(String[]args)
	{
		Horse h=new Horse();
		h.eat();
	}
}

ERROR because eat() is defined two times in the class Horse.
now please tell me how to resolve error in this code?

If you define the same method in two interfaces, make sure that return type also is same, or else it will not get compiled

[Astha Sharma]

okey...thanks Sachin. But if...in case we didn't write the interfaces. They are written by another programmer. We just have to implement them. What can be done then?

[sachin potu]

if i am not wrong , At that time you cannot do any thing, except having two different implementations.

like, HorseImplAnimal and HorseImplBird

[Astha Sharma]

yeah...I too think so

thanks

[Christopher Arthur]

sachin potu wrote:if i am not wrong , At that time you cannot do any thing, except having two different implementations.

like, HorseImplAnimal and HorseImplBird

or like Pegasus...
have you tried to reference the interface by (Bird) SomeHorse.eat() or (Animal)SomeHorse.eat()?

[Astha Sharma]

Christopher Arthur wrote:

or like Pegasus...
have you tried to reference the interface by (Bird) SomeHorse.eat() or (Animal)SomeHorse.eat()?

not getting you. Are you telling to upcast the Horse object to the objects of Bird and Animal?
Even if we try that, error remain in definition of class Horse because here eat() is defined two times.

[Matthew Brown]

Part of the problem here is a poorly designed interface.

If you think about it, it would make sense for the general meaning of the method eat() to be the same for both an Animal and a Bird. In which case, it would be possible to have a single methodthat is an acceptable implementation of the eat() method in both interfaces. The only reason that you can't is that they have different return types. But why? Why does eat() return an int in the Bird class? That doesn't make any sense.

[Arjun Srivastava]

Like Linked-list class implementing both Queue and List interface.
Did you ever encountered any method with same name here in both interface but with different return type?