CS 002-CS21S1: Advanced OOP - Constructors
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Questions and Answers

What is the purpose of a constructor in object-oriented programming?

  • To assign initial values to fields in a class. (correct)
  • To manage memory allocation.
  • To define methods only.
  • To create new classes.

    • What happens when no constructor is defined for a class?

  • The object will be created with random values.
  • The program will output an error.
  • A default constructor is created by the interpreter. (correct)
  • The fields will remain uninitialized.

    • Which of the following is the default value assigned to numeric fields by a default constructor?

  • null
  • 0 (correct)
  • 1
  • false

    • What is the effect of defining a constructor in a class?

    <p>The default constructor will not be created.</p> Signup and view all the answers

    Which of the following represents the default value for Boolean fields when no constructor is defined?

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

    How must a constructor be defined in a class?

    <p>Public and matching the class name.</p> Signup and view all the answers

    What value does a default constructor assign to character fields?

    <p>'\u0000' (Unicode empty character)</p> Signup and view all the answers

    What is meant by instantiation in object-oriented programming?

    <p>The process of creating an instance of a class.</p> Signup and view all the answers

    What is the purpose of the 'this' keyword in a class method?

    <p>To refer to the current instance of the class</p> Signup and view all the answers

    Why might using the same variable name for both a method parameter and an instance field cause confusion?

    <p>It creates ambiguity about which variable is being referenced.</p> Signup and view all the answers

    In the provided example, what does the method changeName(String name) do?

    <p>Assigns the parameter 'name' to the instance field 'name'.</p> Signup and view all the answers

    What happens if the 'this' keyword is omitted in the method changeName(String name)?

    <p>The parameter name will be incorrectly assigned to itself.</p> Signup and view all the answers

    Which of the following best describes the instance field in the class Person?

    <p>It is a variable that holds a value specific to an instance of the class.</p> Signup and view all the answers

    When using the new keyword, what is being created in the context of the class Person?

    <p>An instance of the Person class</p> Signup and view all the answers

    How does the 'this' keyword improve code readability?

    <p>By clarifying which variable is being referred to</p> Signup and view all the answers

    What type of access modifier is used for the field name in the class Person?

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

    What is the access modifier of the 'isPowered' variable in the LightBulb class?

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

    Which method in the LightBulb class is responsible for changing the state from off to on?

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

    What do the parameters of the LightBulb constructor represent?

    <p>The color of the light bulb and its energy consumption.</p> Signup and view all the answers

    Which statement accurately describes a characteristic shared by constructors?

    <p>They can be overloaded just like methods.</p> Signup and view all the answers

    What does the checkStatus method return?

    <p>A boolean indicating if the light is powered on.</p> Signup and view all the answers

    What is the initial value of the 'isPowered' variable when a LightBulb object is created?

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

    What will be the effect of calling the flipSwitch method when the bulb is off?

    <p>The bulb will turn on.</p> Signup and view all the answers

    Which of the following methods would you use to retrieve the color of the LightBulb?

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

    Which of these statements about the LightBulb class is correct?

    <p>It encapsulates properties relevant to a light bulb.</p> Signup and view all the answers

    What does the checkWatts method return?

    <p>An integer representing the wattage of the bulb.</p> Signup and view all the answers

    Study Notes

    Constructors in Object-Oriented Programming

    • Constructors are special methods invoked when an instance of a class is created, referred to as instantiation.
    • They allow the assignment of initial values to fields within a class.
    • A constructor is optional; if not defined, a default constructor is created by the interpreter.

    Default Constructor Behavior

    • The default constructor assigns standard values based on field types:
      • Numeric fields get a default value of 0.
      • Character fields receive the Unicode empty character '\u0000'.
      • Boolean fields default to false.
      • Object fields are set to null.
    • If a custom constructor is defined, the default constructor will not be created.

    Writing a Constructor

    • A constructor must include:
      • public modifier to make it accessible.
      • Class name as the constructor's name.
      • Parentheses to enclose the parameter list.
      • A parameter list, similar to methods.

    Example: LightBulb Class

    • The LightBulb class demonstrates a constructor for initializing properties:
      • Private fields: isPowered (boolean), watts (int), color (String).
      • Constructor initializes these fields.
      • Methods implement functionality to turn the bulb on/off and check status, color, and wattage.

    Characteristics of Constructors

    • Constructors do not have a return type, as they return an instance of the object.
    • They are always triggered when using the new keyword to create an object.

    Using the this Keyword

    • The this keyword refers to the current instance of the class, helping to resolve name conflicts between parameters and object fields.
    • In the Person class example, the changeName method uses this.name to distinguish between the class field and the parameter named name.

    Assignment Reminder

    • A link is provided for further assignments related to constructors.

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    Quiz Team

    Description

    Test your knowledge on constructors in Advanced Object-Oriented Programming. This quiz covers key concepts and functionalities of constructors as outlined in the syllabus for CS 002. Prepare to demonstrate your understanding and application of these fundamental programming principles.

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