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Questions and Answers
What is the primary relationship between a subclass and its superclass?
What does a subclass inherit from its superclass?
What can a subclass do in addition to inheriting from its superclass?
What is a new feature present in the Circle class that is not present in the GeometricObject class?
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Which of the following classes is a subclass of the GeometricObject class?
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What is the symbol used to denote the inheritance relationship between two classes?
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What is the purpose of the keyword extends in the Circle class?
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Why can't we access the data fields color and filled directly in the constructor of the Circle class?
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How can we access the private data fields color and filled in the GeometricObject class?
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What is the result of attempting to use the data fields color and filled directly in the constructor of the Circle class?
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What is the relationship between the Circle class and the GeometricObject class?
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What happens when the Circle class extends the GeometricObject class?
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What is the keyword used to define a subclass in Java?
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What is the relationship between the Tree and Person classes in terms of inheritance?
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Do subclasses inherit constructors from their superclasses?
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How can a superclass's constructor be invoked from a subclass?
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What is the syntax to call a superclass's constructor with arguments?
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What is the rule for using the 'super' keyword in a subclass constructor?
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What is the first constructor that gets invoked when a new Faculty object is created?
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What is the output of the statement new Faculty()?
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What is the purpose of the statement this("(2) Invoke Employee’s overloaded constructor") in the Employee's no-arg constructor?
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What is the relationship between the classes Faculty, Employee, and Person?
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What is the order of constructor invocation when a new Faculty object is created?
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Why is the no-arg constructor of Employee invoked when a new Faculty object is created?
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What is the main purpose of overriding a method in a subclass?
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Why can a private method not be overridden in a subclass?
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What happens when a static method is redefined in a subclass?
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What is the difference between method overloading and overriding?
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Why can a subclass inherit a static method from its superclass?
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What is the purpose of the toString() method in the Circle class?
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Study Notes
Constructors and Inheritance
- The
Faculty
class extends theEmployee
class, which in turn extends thePerson
class. - When a new
Faculty
object is created, the constructors ofFaculty
,Employee
, andPerson
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()
orsuper(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.