Inheritance in Object-Oriented Programming

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Questions and Answers

How does inheritance primarily contribute to productivity in object-oriented programming?

  • By enabling code sharing based on polymorphism. (correct)
  • By enforcing strict data encapsulation.
  • By automatically optimizing memory usage.
  • By reducing the need for complex algorithms.

How does inheritance aim to bridge the gap between human understanding and programming concepts?

  • By mirroring the structure of hardware components.
  • By translating code directly into natural language.
  • By organizing concepts from general to specific. (correct)
  • By forcing programmers to think in a non-hierarchical manner.

In the context of the Employee and Manager class example, what benefit does inheritance provide when creating the Manager class?

  • It simplifies the deployment process by bundling both classes into a single executable.
  • It allows the `Manager` class to reuse `Employee` functionalities, extending or modifying them as needed. (correct)
  • It allows the `Manager` class to automatically handle all employee payroll functions.
  • It prevents the 'Manager' class from accidentally accessing sensitive employee data.

In object-oriented programming, what does it mean for a subclass to 'override' a method from its superclass?

<p>To replace the superclass's implementation of the method with its own implementation. (A)</p>
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Considering a class Animal with a method makeSound(), and a subclass Dog that overrides makeSound(), what concept does this exemplify?

<p>Polymorphism (A)</p>
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Why is it a common misconception that a Manager class, inheriting from an Employee class, is superior?

<p>Because the 'is-a' relationship is misunderstood to imply superiority instead of a subset relationship. (A)</p>
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In an inheritance hierarchy, where are the most general concepts typically located?

<p>At the root of the tree. (C)</p>
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Which principle states that you can use a subclass object whenever a superclass object is expected?

<p>Liskov's Substitution Principle. (D)</p>
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What does the acronym SOLID stand for in the context of object-oriented design principles?

<p>Single responsibility, Open/closed, Liskov substitution, Interface segregation, and Dependency inversion. (A)</p>
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Which access modifier, when applied to a member in a superclass, allows access to that member in any subclass, regardless of the package?

<p><code>protected</code> (A)</p>
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Why can't a subclass directly access a private field of its superclass?

<p>To enforce strict encapsulation and data hiding in the superclass. (A)</p>
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What is the risk of calling a superclass method directly (without using the super keyword) within an overridden method of a subclass, intending to extend the superclass's behavior?

<p>It can lead to a stack overflow error due to infinite recursion. (A)</p>
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In Java, what is the purpose of the super keyword when calling a method in a subclass?

<p>It calls the superclass's version of the method, bypassing polymorphism. (D)</p>
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When invoking a superclass constructor from a subclass constructor, what is a critical rule regarding the call to super()?

<p>It must be the first statement in the subclass constructor. (A)</p>
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If a subclass constructor does not explicitly call super(), what condition must be met by the superclass?

<p>The superclass must have a constructor with no parameters. (A)</p>
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In Java, which class do all classes implicitly extend if they don't explicitly extend another class?

<p>The <code>Object</code> class. (C)</p>
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Considering that Manager extends Employee, and Employee extends Object, what order are the constructors called during the instantiation of a Manager object?

<p><code>Object</code>, then <code>Employee</code>, then <code>Manager</code>. (C)</p>
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In the context of inheritance, how does Java enforce a tree-type hierarchy?

<p>By allowing a class to inherit from only one superclass. (D)</p>
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Besides code reuse, how can inheritance aid in software design?

<p>By modeling taxonomies and structuring knowledge. (B)</p>
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What is one key aspect a subclass can do with inherited code while adhering to Liskov's substitution principle?

<p>Override, extend, adjust, or refine inherited code. (B)</p>
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Flashcards

What is Inheritance?

A key concept of OO programming that promotes code sharing and polymorphism, matching human understanding of systems with a hierarchy of abstractions.

What is a Subclass?

A class that inherits from another class, acquiring its properties and behaviors.

What is a Superclass?

A class from which other classes inherit, providing common properties and behaviors.

What does 'add new field' mean?

Adding a new field to a class (e.g., adding 'bonus' to Manager class).

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What does 'add new method' mean?

Adding a new method to a class (e.g., adding 'setBonus' to Manager class).

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What does 'override' mean?

Redefining a method in a subclass that is already defined in its superclass.

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What is inherited?

Methods and fields inherited from a superclass are accessible in the subclass.

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What is the Substitution Principle?

A principle stating that a subclass object can be used wherever a superclass object is expected.

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What is Liskov's substitution principle?

A design principle stating objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program.

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What is the 'super' keyword?

The keyword used in a subclass to call a method or constructor of its superclass.

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How to call superclass constructor?

Using the 'super' keyword in a subclass constructor to call the constructor of its superclass.

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Instantiation of subclasses

During instantiation of a subclass, space is allocated for the superclass and the subclass, with the subclass containing the members of both.

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Study Notes

  • Inheritance is a key concept in Object-Oriented (OO) programming that enhances productivity through code sharing via polymorphism
  • It facilitates a match between human understanding of systems and programming language concepts
  • Inheritance involves a hierarchy of abstractions that moves from general concepts to refined, detailed, and specialized realizations

Modeling Specialization

  • Inheritance starts with a simple Employee class, which can be extended to create a Manager class
  • The Manager class is a subclass of the Employee class and can have identical functionality, functionality that appears the same but requires a different internal implementation, or additional functionality
  • The Manager class adds a new field called "bonus"
  • It also adds a new method called "setBonus"
  • The Manager class overrides the existing "getSalary" method to include salary and bonus
  • The "getName" and "setSalary" methods are inherited from the Employee class, demonstrating code reuse

Manager Class Methods and Fields

  • "setSalary" and "getName" methods are inherited from the Employee class
  • "getSalary" method is overridden in the Manager class
  • "setBonus" method is defined specifically for the Manager class
  • The "bonus" field is defined in the Manager class
  • The "name" and "salary" fields are defined in the Employee class

Super/Sub Terminology

  • "Manager" is a subclass because the set of managers is a subset of the set of employees

Inheritance Hierarchies

  • Hierarchies describe general/specific relationships in the real world
  • General concepts are at the root, and more specific concepts are children
  • In programming, the inheritance hierarchy involves a general superclass at the root
  • More specific subclasses are children

The Substitution Principle

  • Barbara Liskov formulated the substitution principle
  • A subclass object can be used wherever a superclass object is expected
  • This principle is fundamental to inheritance

Example of The Substitution Principle

  • You can set a superclass reference to an object of a subclass.
  • Polymorphism ensures the correct overridden method is invoked when called on the superclass reference

SOLID Principles in OO Design Context

  • Single Responsibility Principle (SRP): a class should have only one responsibility
  • Open/Closed Principle (OCP): software entities should be open for extension but closed for modification and suggests using inheritance from abstract base classes and keeping the interface fixed
  • Liskov's Substitution Principle (LSP): objects in a program should be replaceable with instances of their subtypes without altering the correctness of the program
  • Interface Segregation Principle (ISP): many client-specific interfaces are better than one general-purpose interface
  • Dependency Inversion Principle (DIP): Depend upon Abstractions and Do not depend upon concretions

Technicalities: Inheritance and Access Modifiers

  • Method and instance variable access in the subclass is controlled by the access modifier in its declaration
  • The following table shows the access to members permitted by each modifier
Modifier Class Package Subclass World
Public Y Y Y Y
Protected Y Y Y N
No Modifier Y Y N N
Private Y N N N

Technicalities: Invoking Superclass Methods

  • Private fields of the superclass cannot be accessed directly
  • When calling a superclass method, avoid recursive calls by not using the method's name directly

Super Keyword

  • The "super" keyword is used to call the superclass's method with the same name.
  • "super" is not a reference
  • "super" turns off the polymorphic call mechanism, ensuring the superclass's version is executed

Technicalities: Invoking Superclass Constructors

  • Use the "super" keyword in the subclass constructor to call the superclass constructor
  • The call to "super" must be the first statement in the subclass constructor
  • If the subclass constructor does not explicitly call "super", the superclass must have a constructor without parameters

Instantiation of subclasses technicalities

  • A Manager class explicitly "extends" the Employee class
  • An Employee class implicitly extends the Object class

Example of Instantiation of subclasses

  • When a new Manager object is created, space is allocated for the Manager, Employee, and Object components in memory
  • When "new Manager("Alice")" is called, first the Object constructor is invoked, followed by the Employee constructor, and then the Manager constructor

Summary of Inheritance

  • Inheritance describes an "is-a" relationship, where subclasses are specialized versions of a generic superclass
  • Consider a Venn diagram for subset relationships or a taxonomy/tree-type hierarchy from general to specific
  • The Java syntax class mySubClass extends mySuperClass is used
  • A class can inherit from only one superclass, forming a tree-type hierarchy
  • Subclasses inherit code but can override, extend, adjust, and refine it, adhering to Liskov's substitution principle

Inheritance in Software (SW) Design

  • Taxonomies can structure human knowledge, aiding in understanding complex systems
  • Inheritance can model taxonomies, facilitate code sharing among classes to inherit code among classes

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