Polymorphism in Object-Oriented Programming

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Questions and Answers

What happens when trying to assign an Object to a Student without casting?

It works perfectly as Object can be cast to any type.

It results in an implicit cast.

It results in a compilation error. (correct)

It throws a runtime exception.

Which statement is true regarding explicit casting in Java?

It can be performed without any knowledge of the object type.

Explicit casting does not require any checks before casting.

It requires that the object is guaranteed to be of the target class. (correct)

Explicit casting can only be performed on primitive data types.

How can you safely check if an object can be cast to a specific class before attempting to cast it?

By checking the class name of the object.

Implicitly casting the object without checks.

Utilizing the instanceof operator. (correct)

Using a try-catch block.

What is the correct syntax to create an instance of an ArrayList in Java?

ArrayList cityList = new ArrayList<>(); Signup and view all the answers

When removing an item from an ArrayList by index, what is the consequence of passing an index that is out of bounds?

It throws an IndexOutOfBoundsException. Signup and view all the answers

What is the primary benefit of using polymorphism in Object-Oriented Programming?

It allows for less code duplication. Signup and view all the answers

Which type of polymorphism is determined at compile time?

Static Polymorphism Signup and view all the answers

How is dynamic polymorphism primarily achieved?

Overriding methods in subclasses. Signup and view all the answers

What is an abstract class?

A class that serves as a template with abstract methods. Signup and view all the answers

In polymorphism, which factor differentiates static binding from dynamic binding?

Method resolution time. Signup and view all the answers

What keyword is used to define an abstract class in Java?

abstract Signup and view all the answers

Which statement correctly describes an interface in Java?

It consists only of abstract methods and constants. Signup and view all the answers

What needs to happen for a subclass to use an interface?

The subclass must implement the interface methods. Signup and view all the answers

What is the purpose of the 'instanceof' operator?

To check the type of an object at runtime. Signup and view all the answers

What differentiates method overloading from method overriding?

Overloading uses different method signatures in the same class. Signup and view all the answers

Which of the following is true regarding the ArrayList class?

It can dynamically resize based on elements added. Signup and view all the answers

Why can’t you create an instance of an abstract class?

It may not implement all methods. Signup and view all the answers

Which feature allows subclasses to implement methods that were defined in an abstract class?

Abstraction Signup and view all the answers

What is the key difference between an abstract class and an interface?

An abstract class can contain instance fields, while an interface cannot. Signup and view all the answers

Study Notes

Polymorphism

Polymorphism means many forms / shapes
Object-oriented concept
One of the 3 pillars of OOP (Encapsulation, Inheritance, Polymorphism)
Efficient and less redundancy

Types of Polymorphism

Static polymorphism (compile-time polymorphism)
- Achieved by using method overloading
- Several methods in a class with the same name but different parameters
- Java knows which method to call at compile time by checking method signatures

Static Polymorphism Example

Using the Calculator class
- add(int x, int y)
- add(int x, int y, int z)
- add(double x, double y)
- add(double x, double y, double z)

Dynamic Polymorphism

Achieved by overriding, implementing abstract classes, or implementing interfaces
Dynamic binding (Runtime polymorphism)
Method to call is determined at runtime

Dynamic Polymorphism Example - Overriding

Using the Vehicle class
- move()
Using the MotorBike class that extends Vehicle
- move() overrides the move() method in Vehicle

Dynamic Polymorphism Example - Abstract Classes

Declare general characteristics of subclasses
Abstractly declared
Cannot create an object using the new operator
Used as superclasses for other classes
Declared using the abstract keyword
Superclass must be concrete

Dynamic Polymorphism Example - Abstract Classes (continued)

A template for subclass design
Provides abstract functions
Function overridden in subclasses
An object must implement all abstract methods in an abstract class

Dynamic Polymorphism Example - Implementing Abstract Class

Shape abstract class
- Abstract method computeArea()
Rectangle class extends Shape
- Overridden computeArea() method
Circle class extends Shape
- Overridden computeArea() method

Dynamic Polymorphism Example - Interface Classes

Consist of constants and abstract methods
Cannot create an object using the new operator
Create subclasses with multiple superclasses (multiple inheritance solution)
Not inherited, but implemented
Declared using the interface keyword
Implemented in subclasses using the implements keyword

Dynamic Polymorphism Example - Interface Classes (continued)

Each interface is compiled into bytecode
All methods declared in the interface must be overridden by the implementing class

Dynamic Polymorphism Example - Implementing Interface Class

Animal interface
- Abstract methods: eat(), travel()
Mammal class implements Animal
- Overridden eat() and travel() methods

Interface vs Abstract Class

Casting Objects

Converting one object to another type in an inheritance hierarchy
Two types:
- Implicit casting
- Explicit casting
Error if a class object is cast to a class object that is not its superclass
Ensure that the object is an instance of another object before casting using the instanceof operator

ArrayList

Constructing an ArrayList: ArrayList cityList = new ArrayList();
Adding a string to the ArrayList: cityList.add("Aachen");
Removing a specific string: cityList.remove("Dresden");
Removing a string by index: cityList.remove(1);

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Description

Explore the concept of polymorphism in object-oriented programming, focusing on its two types: static and dynamic polymorphism. This quiz will test your understanding of method overloading, overriding, and real-world examples using classes like Calculator and Vehicle.