Inheritance in Java Flashcards
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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?

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

"is a" is a part of what concept?

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

When a subclass inherits fields and methods from a superclass, are they included in the subclass?

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

What keyword indicates that a subclass inherits from a superclass?

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

In a UML diagram, how do we indicate that a subclass extends a superclass?

<p>We use an open arrow head pointing from the subclass to the superclass.</p> Signup and view all the answers

We can say that a subclass is a specialized version of the superclass.

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

Given two classes, Auto() and SportsCar() which extends Auto(), when a new SportsCar object is created, what object is created first?

<p>An object of the superclass Auto() is created first.</p> Signup and view all the answers

Can private members of the superclass be accessed by the subclass?

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

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?

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

SuperClass constructors are inherited.

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

When a subclass is instantiated, the superclass _____________ constructor is executed first.

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

When a subclass is instantiated, what is instantiated first?

<p>The superclass default constructor.</p> Signup and view all the answers

What does the super keyword refer to?

<p>The superclass.</p> Signup and view all the answers

What happens if you have written your own constructor in the superclass and omit the default constructor?

<p>You must add a no-arg constructor or call the superclass constructor from the subclass.</p> Signup and view all the answers

Must the call to the superclass constructor be the first Java statement in the subclass constructor?

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

If the superclass does not have a default no-arg constructor, what must happen?

<p>Every subclass must explicitly invoke the superclass constructor using the keyword SUPER.</p> Signup and view all the answers

How can a subclass method invoke the overridden method found in the superclass?

<p>By using the super keyword.</p> Signup and view all the answers

What is a protected member?

<p>Protected members may be accessed by methods in a subclass and by methods in the same package.</p> Signup and view all the answers

In a UML diagram, how is a protected member designated?

<h1></h1> Signup and view all the answers

How do we prevent a method from being overridden in the superclass by a subclass?

<p>By using the final modifier.</p> Signup and view all the answers

What is the Object class?

<p>The Java API has a class named Object, which all other classes directly or indirectly inherit from.</p> Signup and view all the answers

Why does every class have a toString or equals method?

<p>Because every class inherits from the Object class.</p> Signup and view all the answers

Can static members be overridden?

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

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 extends signifies 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 super keyword 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 final modifier in the superclass method definition.

Object Class and Static Members

  • All classes in Java inherit from the Object class, which provides fundamental methods like toString and equals.
  • Every class has a toString and equals method 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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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.

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