Polymorphism/Inheritance Practice
Can a parameter to a method i.e. "catch(Animal a)" be polymorphic?
A method can accept a polymorphic reference; this may give the method more flexibility than it would otherwise have.
What is a polymorphic reference?
A polymorphic reference can point to multiple types of objects at different points in time
How can you declare an abstract method?
An abstract method is a method header without a method body
What is an interface?
An interface is mostly a collection of abstract methods
Can an interface declare instance variables?
An interface may declare constants, but it may not declare instance variables.
What does it mean "public class A implements B"?
Class A accepts the contract of class B. Class A has to implement all methods of class B
Can a polymorphic reference invoke a method that is only declared at the object's class level?
In general, a polymorphic reference can only be used to invoke methods that are known to the class of the reference variable. In order to call a method that is declared at the object's class level, the reference variable must be cast to be of the object's type as part of the call.
How does inheritance relate to polymorphism in Java?
Inheritance is one process by which polymorphic references are created. A reference to a type higher in an inheritance hierarchy can always refer to an object of a type lower in an inheritance hierarchy due to the is-a relationship.
How does interfaces relate to polymorphism in Java?
Interface is one process by which polymorphic references are created. A reference to a type higher in an interface hierarchy can always refer to an object of a type lower in an interface hierarchy due to the is-a relationship.
Is static binding or dynamic binding more efficient?
Late binding is less efficient than compile-time binding due to the overhead associated with determining the code that should be executed at run time.
Do we need dynamic binding for method overloading or overriding?
Method overriding is responsible for dynamic binding, because the compiler cannot resolve it at compile time. The actual object having a method invoked on it could possible be one of several.
Is it possible to instantiate an interface?
No, an interface cannot be instantiated, because it only contains abstract methods.
What is polymorphism?
Polymorphism is the ability of an object to take on many forms.
What is the difference between static and dynamic binding?
Static binding in Java occurs during compile time while dynamic binding occurs during runtime. Static binding uses Type (class in Java) information for binding while dynamic binding uses object to resolve binding.
What is the purpose of an abstract method?
The purpose of an abstract method is, that each class which extends/ implements the superclass /interface has to implement this method
Can a reference " Animal a " only point to an object created by instantiating the Animal class?
This reference may point to an object of any type that is compatible with Animal. In particular, it may point to any object that is an instance of a class that is a subclass of Animal.
Can an interface hierarchy be used for polymorphism?
Yes. A reference variable can use an interface as its type, and can then refer to objects of classes that implement the interface. In this way, polymorphism works the same as it does with an inheritance hierarchy.
Are there any differences between extending a class and implementing an interface?
Yes. First, extending a class uses the extends keyword, while implementing an interface uses the implements keyword. More importantly, a class can implement multiple interfaces, while it can only extend a single class.
Do we need dynamic binding for variable shadowing?
private, final and static methods and variables use static binding
