Java interface

public interface Relatable {     public int isLargerThan(Relatable other); }
class A implements Relatable{

public int isLargerThan(Relatable other) {     RectanglePlus otherRect = (RectanglePlus)other; // Why that way?     if (this.getArea() < otherRect.getArea())     return -1;     else if (this.getArea() > otherRect.getArea())     return 1;     else     return 0;     
    }
class B implements Relatable{

public Object findLargest(Object object1, Object object2) {    Relatable obj1 = (Relatable)object1;    Relatable obj2 = (Relatable)object2;    if ( (obj1).isLargerThan(obj2) > 0) //Here Iam again using method but I dont declare it in that class, is it correct??       return object1;    else        return object2;         }
}

Source: 
http://download.oracle.com/javase/tutorial/java/IandI/usinginterface.html