Questions and Answers
Are private fields and methods of the superclass inherited in the subclass?
False
If a subclass constructor does not explicitly call a superclass constructor, what will Java automatically do?
Java will automatically call the superclass's default constructor.
Can a method be overloaded and simultaneously be overriding a method in a superclass?
True
"has a" is a part of what concept?
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"is a" is a part of what concept?
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When a subclass inherits fields and methods from a superclass, are they included in the subclass?
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What keyword indicates that a subclass inherits from a superclass?
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In a UML diagram, how do we indicate that a subclass extends a superclass?
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We can say that a subclass is a specialized version of the superclass.
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Given two classes, Auto() and SportsCar() which extends Auto(), when a new SportsCar object is created, what object is created first?
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Can private members of the superclass be accessed by the subclass?
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Given a superclass with a private field numHours, is the statement 'SubClass child = new SubClass(); println("My child studies " + child.numHours + " hours a day.")' syntactically correct?
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SuperClass constructors are inherited.
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When a subclass is instantiated, the superclass _____________ constructor is executed first.
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When a subclass is instantiated, what is instantiated first?
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What does the super keyword refer to?
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What happens if you have written your own constructor in the superclass and omit the default constructor?
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Must the call to the superclass constructor be the first Java statement in the subclass constructor?
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If the superclass does not have a default no-arg constructor, what must happen?
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How can a subclass method invoke the overridden method found in the superclass?
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What is a protected member?
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In a UML diagram, how is a protected member designated?
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How do we prevent a method from being overridden in the superclass by a subclass?
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What is the Object class?
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Why does every class have a toString or equals method?
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Can static members be overridden?
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Study Notes
Inheritance Principles
- Private fields and methods of the superclass are not inherited by the subclass.
- If a subclass constructor does not call a superclass constructor, Java automatically invokes the superclass's default (no-arg) constructor.
- Methods can be both overloaded and overridden in subclasses—overloading occurs when methods share the same name but differ in parameters.
Concepts in Object-Oriented Design
- The term "has a" relates to the concept of aggregation, indicating a whole-part relationship.
- The term "is a" relates to inheritance, illustrating a hierarchical relationship between classes.
- When a subclass inherits fields and methods from a superclass, they are not physically included in the subclass's memory.
Relation Indicators
- The keyword
extendssignifies that a subclass inherits from a superclass. - In UML diagrams, inheritance is represented with an open arrowhead pointing from the subclass to the superclass.
Object Creation and Constructors
- A subclass can be seen as a specialized version of the superclass, inheriting its properties and behaviors.
- When a new object of a subclass is created, the superclass's constructor is executed before the subclass's constructor.
- If a superclass has a private field (e.g.,
numHours), it cannot be accessed directly by the subclass. - Superclass constructors are not inherited by subclasses; each subclass must invoke the superclass constructor if needed.
Default Constructor and Overriding
- The superclass's default constructor is executed first when a subclass is instantiated.
- If a superclass lacks a default no-arg constructor, all subclass constructors must explicitly call a constructor from the superclass.
- The
superkeyword is essential for invoking the superclass's constructor and accessing its members.
Access Modifiers and Method Overriding
- Protected members are accessible by methods in the subclass and methods within the same package, ensuring controlled access.
- In UML, a protected member is denoted with a
#. - To prevent a method from being overridden in a subclass, use the
finalmodifier in the superclass method definition.
Object Class and Static Members
- All classes in Java inherit from the Object class, which provides fundamental methods like
toStringandequals. - Every class has a
toStringandequalsmethod because they inherit from the Object class. - Static members belong to a class and cannot be overridden by subclasses, as they are not tied to instances.
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Description
Test your knowledge of inheritance in Java with these flashcards. Covering key concepts such as visibility of fields and automatic constructor calls, these flashcards are perfect for anyone needing a refresher on Java inheritance principles.
