Introduction to Object-Oriented Programming

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Questions and Answers

What does CSS primarily define for HTML elements?

How elements are displayed on various media (correct)

The method of variable declaration

The data types used in JavaScript

The logical operations in code

Which of the following correctly describes the 'inline' method of adding CSS?

It defines styles for all pages within a website.

It applies styles to multiple web pages simultaneously.

It is used to style the entire document.

It uses the style attribute of an HTML element. (correct)

What is the purpose of JavaScript variables?

They store data values and are declared using the var keyword. (correct)

They are used to build the layout of web pages.

They store the presentation style of an HTML element.

They control the flow of CSS styles.

What does the '==' operator do in JavaScript?

Tests for abstract equality with necessary type conversions. Signup and view all the answers

How can external CSS be linked to multiple HTML pages?

By adding a link in the head section of the HTML document. Signup and view all the answers

Which statement about CSS selectors is true?

They define patterns used to select HTML elements for styling. Signup and view all the answers

What is the role of the equal sign in JavaScript variables?

It assigns values to variables. Signup and view all the answers

Which of the following is NOT a way to add CSS to HTML elements?

JavaScript functions Signup and view all the answers

What is the purpose of method overriding in object-oriented programming?

To provide a specific implementation of a method already defined in the parent class Signup and view all the answers

Which of the following correctly describes polymorphism?

Ability for different classes to be treated as instances of the same class through a common interface Signup and view all the answers

Which of the following is NOT a type of constructor?

Static constructor Signup and view all the answers

What is constructor overloading?

Creating multiple constructors with different parameter lists Signup and view all the answers

Which keyword is used to indicate inheritance in Java?

extends Signup and view all the answers

What is the primary disadvantage of multiple inheritance in Java?

It complicates the method resolution order and can lead to ambiguity Signup and view all the answers

What is one of the main advantages of inheritance?

It allows methods to be overwritten for specific use cases Signup and view all the answers

Which of the following is NOT a characteristic of an object?

Must have explicit return type Signup and view all the answers

In what scenario is a default constructor provided by the compiler?

Only when no constructor is defined by the user Signup and view all the answers

What is the relationship represented by inheritance?

IS-A relationship Signup and view all the answers

What is the minimum requirement to define a class in Java?

Must have an access modifier Signup and view all the answers

Which type of inheritance implies a parent-child relationship where the child inherits from one parent?

Single inheritance Signup and view all the answers

Which statement is true regarding parameterized constructors?

They provide different values to distinct objects Signup and view all the answers

What is polymorphism in object-oriented programming?

The ability of an object to take on many forms Signup and view all the answers

Which of the following statements about method overriding is true?

Method overriding occurs when a method in a subclass has the same name and parameters as a method in the superclass Signup and view all the answers

How does method overloading increase code reusability?

By allowing methods with the same name to perform different tasks based on parameters Signup and view all the answers

What is the main advantage of using inheritance in programming?

Facilitates code reusability and logical structure Signup and view all the answers

In Java, which type of constructors can a subclass use from its superclass?

All types of constructors if properly invoked Signup and view all the answers

What is a key feature of abstract classes in Java?

They can include both abstract and non-abstract methods. Signup and view all the answers

Which of the following describes the relationship between a parent class and a child class in a polymorphic scenario?

A parent reference can hold a child class object and invoke its methods. Signup and view all the answers

How does encapsulation contribute to method overriding?

It helps in hiding the internal workings of object methods. Signup and view all the answers

Which modifier allows a subclass to inherit a method without changing its behavior?

Final Signup and view all the answers

What is a characteristic of a constructor in Java?

Constructors cannot have return types. Signup and view all the answers

What is the primary purpose of interfaces in Java?

To describe a contract that implementing classes must follow Signup and view all the answers

Which of the following is a benefit of using interface over abstract class?

A class can implement multiple interfaces, allowing flexibility. Signup and view all the answers

Which of the following is true regarding method visibility when using inheritance?

Public methods of a superclass are accessible outside the package. Signup and view all the answers

What happens when you declare a method in a class as final?

Its implementation cannot be changed in subclasses. Signup and view all the answers

Study Notes

Object

An entity that has state and behavior
Can be defined as an instance of a class
Contains an address
Takes up space in memory
Can communicate without knowing details of other objects' data or code. Only needs to know the type of message accepted and response type by the objects.
Must have no explicit return type
Cannot be abstract, static, final, and synchronized

Class

Templates used to create objects and define object data types and methods
Core properties: data types and methods
Can be defined as a blueprint
Don't consume space
A blueprint for creating individual objects

Advantages of OOPs over Procedure Oriented Programming

Easier development and maintenance
Procedure oriented programming is harder to manage if code grows
Provides data hiding
Procedure oriented programming language has global data that can be accessed anywhere.

Constructor

Block of code similar to a method
Called when an object instance is created
Allocates memory for the object
Used to initialize the object
Called when an object is created
Like a method but without a return type
Rules: Method name must be the same as class name

Parameterized Constructor

Has a specific number of parameters
Used to provide different values to different objects

Constructor Overloading

Technique of having one or more constructors with different parameter lists
Each constructor performs a different task
Distinguished by the number and types of parameters

Inheritance

A mechanism where one object acquires all properties and behaviors of a parent object
An important part of OOPs
Can reuse methods and fields of the parent class
Can add new methods and fields in the current class
Represents an "is-a" relationship

Advantages of Inheritance

Method overriding
Code reusability

Multiple Inheritance

Not supported by Java
Reduces complexity and simplifies language
Improves the language

Polymorphism

The ability of an object to take many forms
Parent class references can be used to refer to a child class object

Method Overloading

A class can have multiple methods with the same name but different parameters
Improves readability of the program
Parameters must be different
Compile-time Polymorphism

Static Method Overriding

Not possible
Static methods are bound to the class, not the object

Abstraction

Hiding implementation details and showing only functionality to the user
Focusing on what an object does, not how it does it
Achieved through abstract classes or interfaces

Generalization

Extracting shared characteristics from two or more classes and combining into a generalized superclass

Specialization

Creating new subclasses from an existing class

Abstract Class

Declared abstract
Can have abstract and non-abstract methods
Needs to be extended

Package

Group of similar classes, interfaces, and subpackages
Built-in vs user-defined packages
Organizes code and makes it easier to maintain

Interface

Similar to a class but only has abstract methods
Methods are implicitly abstract and public
Can implement multiple interfaces
Cannot contain instance variables (only static or final)
Cannot instantiate like a class

Class and Interface Similarities

Can have multiple methods
Name of the interface matches the file name
Byte code of the interface appears in a .class file

Differences Between Classes and Interfaces

Interfaces cannot be instantiated
Interfaces cannot have constructors
Methods in interfaces are abstract
Interfaces cannot have instance fields (only static or final)

Exception Handling

Checked Exceptions: Compiler forces you to handle them explicitly in methods. Methods throwing checked exceptions must include a throws clause
Unchecked Exceptions (Errors): Compiler does not enforce handling. Methods don't need a throws clause. Errors typically indicate an exceptional condition not recoverable
Exception Hierarchy: An hierarchy of exception classes, extending from Throwable class. Exception is a subclass of Throwable.

Catching Exceptions

Method catches exception using try and catch keywords
Code prone to exceptions is placed in the try block
Exception handled by corresponding catch block

Throw and Throws

throws is used to declare (or specify), that a method may throw an exception
throw is used to explicitly generate an exception

Finally Block

Always executes, regardless of exception
Used for cleanup actions (resource release).

Arrays

An object that contains elements of a similar data type.
Elements are stored at indices (starting from 0).

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Description

This quiz covers the fundamental concepts of Object-Oriented Programming (OOP), including the definitions of objects and classes, their properties, and advantages over procedure-oriented programming. Additionally, it addresses the role of constructors in object creation. Test your understanding of these essential programming principles.