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Java Programming: Superclasses and Subclasses
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Java Programming: Superclasses and Subclasses

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Questions and Answers

What is the primary relationship between a subclass and its superclass?

  • has-a relationship
  • is-a relationship (correct)
  • part-of relationship
  • uses-a relationship
  • What does a subclass inherit from its superclass?

  • only public methods
  • accessible data fields and methods (correct)
  • all data fields and methods, regardless of access
  • only private data fields
  • What can a subclass do in addition to inheriting from its superclass?

  • only change the access modifier of existing methods
  • only add new data fields
  • add new data fields and methods (correct)
  • only override methods
  • What is a new feature present in the Circle class that is not present in the GeometricObject class?

    <p>radius data field</p> Signup and view all the answers

    Which of the following classes is a subclass of the GeometricObject class?

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

    What is the symbol used to denote the inheritance relationship between two classes?

    <p>A triangular arrow</p> Signup and view all the answers

    What is the purpose of the keyword extends in the Circle class?

    <p>To inherit methods from the GeometricObject class</p> Signup and view all the answers

    Why can't we access the data fields color and filled directly in the constructor of the Circle class?

    <p>Because they are private</p> Signup and view all the answers

    How can we access the private data fields color and filled in the GeometricObject class?

    <p>Through the getter and setter methods</p> Signup and view all the answers

    What is the result of attempting to use the data fields color and filled directly in the constructor of the Circle class?

    <p>It will not compile due to access restrictions</p> Signup and view all the answers

    What is the relationship between the Circle class and the GeometricObject class?

    <p>Circle is a subclass of GeometricObject</p> Signup and view all the answers

    What happens when the Circle class extends the GeometricObject class?

    <p>The Circle class gains the methods of the GeometricObject class</p> Signup and view all the answers

    What is the keyword used to define a subclass in Java?

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

    What is the relationship between the Tree and Person classes in terms of inheritance?

    <p>Tree class inherits Person class</p> Signup and view all the answers

    Do subclasses inherit constructors from their superclasses?

    <p>No, they do not inherit constructors</p> Signup and view all the answers

    How can a superclass's constructor be invoked from a subclass?

    <p>Using the keyword 'super'</p> Signup and view all the answers

    What is the syntax to call a superclass's constructor with arguments?

    <p>super(arguments)</p> Signup and view all the answers

    What is the rule for using the 'super' keyword in a subclass constructor?

    <p>It must be the first statement in the constructor</p> Signup and view all the answers

    What is the first constructor that gets invoked when a new Faculty object is created?

    <p>Person's no-arg constructor</p> Signup and view all the answers

    What is the output of the statement new Faculty()?

    <p>(1) Person's no-arg constructor is invoked (2) Invoke Employee’s overloaded constructor (3) Employee's no-arg constructor is invoked (4) Faculty's no-arg constructor is invoked</p> Signup and view all the answers

    What is the purpose of the statement this("(2) Invoke Employee’s overloaded constructor") in the Employee's no-arg constructor?

    <p>To invoke the overloaded constructor of Employee</p> Signup and view all the answers

    What is the relationship between the classes Faculty, Employee, and Person?

    <p>Faculty is a subclass of Employee, and Employee is a subclass of Person</p> Signup and view all the answers

    What is the order of constructor invocation when a new Faculty object is created?

    <p>Person, Employee, Faculty</p> Signup and view all the answers

    Why is the no-arg constructor of Employee invoked when a new Faculty object is created?

    <p>Because Faculty is a subclass of Employee</p> Signup and view all the answers

    What is the main purpose of overriding a method in a subclass?

    <p>To provide a new implementation of the method that is different from the superclass</p> Signup and view all the answers

    Why can a private method not be overridden in a subclass?

    <p>Because it is not accessible outside its own class</p> Signup and view all the answers

    What happens when a static method is redefined in a subclass?

    <p>The method in the superclass is hidden</p> Signup and view all the answers

    What is the difference between method overloading and overriding?

    <p>Overloading is used for multiple methods with the same name, while overriding is used for a new implementation of a method</p> Signup and view all the answers

    Why can a subclass inherit a static method from its superclass?

    <p>Because a static method is accessible outside its own class</p> Signup and view all the answers

    What is the purpose of the toString() method in the Circle class?

    <p>To return a string representation of the circle</p> Signup and view all the answers

    Study Notes

    Constructors and Inheritance

    • The Faculty class extends the Employee class, which in turn extends the Person class.
    • When a new Faculty object is created, the constructors of Faculty, Employee, and Person are called in that order.
    • The Employee class has an overloaded constructor that takes a string argument, and a no-arg constructor.
    • The Person class has a no-arg constructor.

    Superclasses and Subclasses

    • A subclass inherits accessible data fields and methods from its superclass.
    • A subclass may also add new data fields and methods.
    • The extends keyword is used to denote the inheritance relationship between two classes.
    • A subclass and its superclass must have an "is-a" relationship.
    • Private data fields in a superclass are not accessible outside the class, but can be accessed/mutated through public accessors/mutators if defined in the superclass.

    Using the super Keyword

    • A subclass does not inherit constructors from its superclass.
    • A subclass can invoke its superclass's constructors using the super keyword.
    • The syntax to call a superclass's constructor is super() or super(parameters).
    • The super keyword must be the first statement in the constructor.

    Overriding vs. Overloading

    • Overloading means defining multiple methods with the same name but different signatures.
    • Overriding means providing a new implementation for a method in the subclass.
    • An instance method can be overridden only if it is accessible.
    • A private method cannot be overridden because it is not accessible outside its own class.
    • A static method can be inherited, but it cannot be overridden. If a static method defined in the superclass is redefined in a subclass, the method defined in the superclass is hidden.

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    Description

    This quiz covers the concept of superclasses and subclasses in Java programming, including inheritance relationships, accessible data fields and methods, and the is-a relationship. Learn how a subclass inherits from its superclass and adds new data fields and methods.

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