Object-Oriented Programming
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Questions and Answers

Which keyword is used to declare a variable that can be reassigned in Scala?

  • `const`
  • `val`
  • `var` (correct)
  • `let`

    • In a do-while loop in Scala, the loop's predicate is evaluated before the loop block is executed the first time.

    False (B)

    What is the keyword used to define a mutable object?

    mutable object

    The syntax for a while loop in Scala is while ______ do block

    <p>predicate</p> Signup and view all the answers

    Match the loop types with their descriptions:

    <p><code>while</code> loop = Evaluates the predicate before each execution <code>do-while</code> loop = Evaluates the predicate after each execution <code>for</code> loop = Iterates over a collection or range</p> Signup and view all the answers

    Which of the following is the correct syntax to initialize an array of type Integer with the values 1, 2, and 3?

    <p><code>var array: Array[Int] = Array[Int](1, 2, 3)</code> (A)</p> Signup and view all the answers

    In Scala, reassignment of a variable means changing an existing object.

    <p>False (B)</p> Signup and view all the answers

    In for loops, what is the term for the variable that is used to keep track of the iteration?

    <p>loop variable</p> Signup and view all the answers

    What does the term 'Software Crisis' refer to?

    <p>The inability to manage and control poorly structured code. (C)</p> Signup and view all the answers

    In Scala, arrays declared with val are immutable, meaning their elements cannot be changed.

    <p>False (B)</p> Signup and view all the answers

    What are the two main programming paradigms that emerged in response to the software crisis?

    <p>functional programming and object-oriented programming</p> Signup and view all the answers

    In object-oriented programming, a combination of data and methods is known as a(n) ______.

    <p>object</p> Signup and view all the answers

    Match the following software goals with their definitions:

    <p>Controllability = Ability to regulate software behavior Maintainability = Ability to modify and update software efficiently Clarity = Clear and understandable software code Reusability = Code should be easily reused</p> Signup and view all the answers

    Which of the following best describes the 'state' of an object?

    <p>The condition or set of values of an object's attributes at any given time. (B)</p> Signup and view all the answers

    What is a 'singleton object'?

    <p>An object which only has one copy or instance that can exist. (C)</p> Signup and view all the answers

    Arrays are accessed and modified in Scala using the syntax array(______) where the ______ represents the index of the element you are accessing or modifying

    <p>i</p> Signup and view all the answers

    What keyword is used in Scala to define a singleton object?

    <p>object (C)</p> Signup and view all the answers

    The attributes defined in a singleton object are public by default.

    <p>False (B)</p> Signup and view all the answers

    What does the grow method do in the singleton object Maaax?

    <p>Increases the age by 1</p> Signup and view all the answers

    A class serves as a __________ for creating objects.

    <p>blueprint</p> Signup and view all the answers

    Which of the following is an accessor method in the Maaax object?

    <p>getAge (A)</p> Signup and view all the answers

    You can only have one constructor in a Scala class.

    <p>False (B)</p> Signup and view all the answers

    Match the following components with their descriptions:

    <p>Maaax = A singleton object that includes age and job attributes Lamp = A class defining a blueprint for lamp objects getAge = An accessor method for age changeJob = A mutator method for job</p> Signup and view all the answers

    What is the purpose of the override keyword in the context of the Maaax object?

    <p>To modify predefined methods such as toString</p> Signup and view all the answers

    What is the primary function of the resetMatrCounter method in the Student object?

    <p>It modifies the private variable matrCounter. (D)</p> Signup and view all the answers

    Inheritance allows a subclass to access private attributes of its superclass.

    <p>False (B)</p> Signup and view all the answers

    Name the two subclasses that inherit from the Person superclass.

    <p>Student and Prof</p> Signup and view all the answers

    The hierarchy of classes where a subclass inherits from a superclass is called a __________.

    <p>superclass chain</p> Signup and view all the answers

    Match the following classes to their respective work functionality:

    <p>Student = Study, Study Prof = Hold Monologue Person = Work, work</p> Signup and view all the answers

    Which of the following statements about inclusion polymorphism is true?

    <p>A subclass can be treated as an instance of its superclass. (A)</p> Signup and view all the answers

    The attributes of the Prof subclass include name, age, and salary.

    <p>True (A)</p> Signup and view all the answers

    What is the return type of the isGrownUp method in the Person class?

    <p>Boolean</p> Signup and view all the answers

    What is the main purpose of a constructor in a class?

    <p>To initialize an object's attributes (B)</p> Signup and view all the answers

    Destructors are explicitly implemented in Scala for resource management.

    <p>False (B)</p> Signup and view all the answers

    What keyword is used in Scala to refer to the current object instance?

    <p>this</p> Signup and view all the answers

    The require() method is used to validate parameters before an object is __________.

    <p>created</p> Signup and view all the answers

    Match the following access modifiers with their description:

    <p>private = Accessible only within the class protected = Accessible within the class and its subclasses public = Accessible from any other class or object</p> Signup and view all the answers

    Which of the following is true about companion objects?

    <p>They are singleton objects with the same name as the class. (C)</p> Signup and view all the answers

    Secondary constructors are used to work with the same parameters as the primary constructor.

    <p>False (B)</p> Signup and view all the answers

    In the given class example, what would the power attribute of the Lamp class need to be at least?

    <p>0</p> Signup and view all the answers

    Study Notes

    Object-Oriented Programming in Scala

    • Imperative Programming in Scala: In a purely functional context, the var keyword is forbidden. The val keyword is used for immutability. Reassigning an object to a variable is different from changing an existing object. Mutable objects can be reassigned using val.
    • While-loops: The syntax for while-loops in Scala is while predicate do block. An example is provided for printing numbers 1 to 10.
    • Do-while-loops: Scala supports do-while loops where the predicate is evaluated after the loop block's first execution.
    • For-loops: The syntax for for-loops in Scala is for variable <- collection do block. Iterating over a range of numbers is demonstrated using a to b, where 'a' and 'b' are the range boundaries inclusive. Additional syntax is available for step size, reverse iteration, and more. Refer to documentation for these details.
    • Arrays: Arrays in Scala are similar to those used in other languages. They allow accessing elements in constant time (O(1)) and store elements contiguously in memory. However, resizing arrays is time-consuming. Arrays in Scala are statically typed, meaning you can't mix data types within a single array.
    • Example Initialization: Arrays can be initialized in two ways: using existing values or with an empty array of a given size (e.g., var array: Array[Int] = Array(3, 2, 1, 3) or val array: Array[Int] = new Array[Int](4)). Accessing elements is done by index.
    • Mutable vs. immutable Arrays are mutable. In Scala, creating a new array using val won't prevent you from changing array values.
    • Software Crisis: Around 1965, the rapid creation of poorly structured software produced a significant problem (a crisis). Good software strives for controllability, maintainability, clarity, division of labor, expandability, error prevention, reusability, and flexibility.
    • Objects: The object-oriented paradigm combines data (attributes) and related operations (methods) bundled together. Objects have a particular state and identity.
    • Example Object: The provided example demonstrates an object Maaax with private attributes (age, job), and methods (getAge, getJob, grow, changeJob).

    Classes

    • Classes as Templates: Classes act as templates, specifying the attributes (data elements) and methods (behaviors) for creating new objects of a given type. For example, a lamp class might define power as an attribute, turning or dimming as methods.
    • Constructors: Classes can have primary constructors (defined directly within the class declaration). Secondary constructors are implemented within the class body and must invoke the primary constructor.

    Methods and Attributes

    • Methods and attributes are essential parts of a class.
    • Attributes do not need to be shared among objects of the same class (in contrast to some other languages).
    • Modifiers like private and protected can control the accessibility (scope) of attributes and methods in a class or subclasses, respectively.
    • Requirements should be checked before object creation for correct usage (e.g., power of a lamp being non-negative).

    The this Keyword

    • This keyword holds important meaning in object statements, relating to the current object and it's related methods

    Companion Objects

    • A companion object holds related utility functions, members, or constants within the context of a class.
    • The methods and variables in the companion object are visible within the corresponding class and vice versa.
    • The matr\_counter variable in the Student example illustrates this, allowing for automatic incrementing of the matr variable in student initialization

    Inheritance

    • Inheritance: Classes can inherit attributes and methods from parent or super-classes.
    • Modifiers like override or extends can alter methods functionality in a subclass (overriding)
    • Every class in Scala inherits from the superclass Any which means each class automatically inherits the toString() methods.

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    Description

    This quiz explores the fundamentals of Object-Oriented Programming in Scala, including key concepts like imperative programming, loops, and array usage. It provides a clear understanding of syntax and functionality specific to Scala, making it an excellent resource for those learning the language. Test your knowledge on variable immutability, loop structures, and more in this comprehensive quiz.

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