Object-Oriented Concepts and UML

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Questions and Answers

Which of the following describes the primary purpose of inheritance in object-oriented programming?

  • To ensure that all classes are loosely coupled and independent.
  • To manage object creation and destruction.
  • To enable a class to acquire properties and behaviors from another class, forming an 'is-a-kind-of' relationship. (correct)
  • To define a 'has-a' relationship where one class uses another class.

In Java, what keyword is used to implement inheritance between classes?

  • extends (correct)
  • implements
  • inherits
  • derives

Which of the following is a key characteristic of the 'Composition' relationship between classes?

  • The whole object contains and manages the lifecycle of its parts; if the whole is destroyed, the parts are also destroyed. (correct)
  • It is depicted using an open diamond in UML diagrams.
  • The parts can exist independently of the whole.
  • It represents a weak relationship where objects are loosely coupled.

In UML, what symbol represents a composition relationship between two classes?

<p>A filled diamond (A)</p> Signup and view all the answers

Which concept is exemplified when a subclass provides a specific implementation for a method that is already defined in its superclass?

<p>Method Overriding (C)</p> Signup and view all the answers

What is the correct term for the ability of a single method or object to take on many forms?

<p>Polymorphism (B)</p> Signup and view all the answers

What key characteristic distinguishes Aggregation from Composition?

<p>In aggregation, the child object can exist independently of the parent object, whereas, in composition, the child object's lifecycle is tied to the parent. (B)</p> Signup and view all the answers

In UML, what symbol is used to represent an aggregation relationship between two classes?

<p>Empty Diamond (B)</p> Signup and view all the answers

Which of the following best describes the concept of 'constructor chaining' in Java inheritance?

<p>It refers to the process where a constructor of a subclass automatically calls the constructor of its superclass. (A)</p> Signup and view all the answers

When does method overriding occur in Java?

<p>When a subclass defines a method with the same name, return type, and parameters as a method in its superclass. (A)</p> Signup and view all the answers

What is compile-time polymorphism?

<p>Also known as method overloading, where multiple methods have the same name but different parameters and is resolved at compile time. (C)</p> Signup and view all the answers

In the context of class relationships, what does 'multiplicity' define?

<p>How many instances of one class can be associated with an instance of another class in a relationship. (C)</p> Signup and view all the answers

Using the concept of inheritance, if class 'Car' extends class 'Vehicle', which of the following is true?

<p>Class 'Car' inherits the public and protected members of class 'Vehicle'. (A)</p> Signup and view all the answers

Consider a scenario where a 'University' class has multiple 'Department' objects. If the 'University' is closed down, the 'Department' objects can still exist independently. What type of relationship is this?

<p>Aggregation (C)</p> Signup and view all the answers

Which of the following access modifiers allows a superclass attribute to be directly accessed in a subclass but restricts access from outside the class hierarchy?

<p>Protected (C)</p> Signup and view all the answers

Assume a class Animal has a method makeSound(). A subclass Dog overrides this method. If an Animal object is actually a Dog instance, and makeSound() is called, what behavior would be observed?

<p>The <code>makeSound()</code> method in the <code>Dog</code> class will be executed. (A)</p> Signup and view all the answers

Which is the correct syntax to call the superclass constructor from a subclass constructor in Java?

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

In the context of inheritance, what is 'generalization'?

<p>The process of creating a general class from more specific classes. (D)</p> Signup and view all the answers

Which of the following is a direct benefit of using polymorphism in object-oriented design?

<p>Allows for more flexible and extensible code by enabling objects of different classes to be treated as objects of a common type. (D)</p> Signup and view all the answers

Can a subclass inherit private members of its superclass in Java?

<p>Yes, private members are inherited but not directly accessible. (C)</p> Signup and view all the answers

In a class diagram, what does multiplicity '1..*' signify?

<p>One or more instances. (A)</p> Signup and view all the answers

Consider a 'CPU' class and a 'Computer' class. If a 'Computer' object cannot exist without a 'CPU' and the 'CPU' is created within the 'Computer' class, what type of relationship is likely present?

<p>Composition (B)</p> Signup and view all the answers

If a method in a superclass is overridden in a subclass, which method is called when an object of the superclass type, referring to a subclass instance, calls the method?

<p>The subclass's method. (C)</p> Signup and view all the answers

What happens during constructor chaining when you create an instance of a subclass?

<p>The constructors of all superclasses are executed first, starting from the topmost superclass down to the subclass. (B)</p> Signup and view all the answers

Which of the following scenarios best exemplifies method overriding?

<p>A subclass provides a new implementation for a method that is already defined in its superclass with the same signature. (A)</p> Signup and view all the answers

Assume a class Shape with a method area() that returns 0.0. Subclasses Circle and Rectangle override this method to calculate the area specific to their shapes. What is this an example of?

<p>Polymorphism through method overriding (D)</p> Signup and view all the answers

In UML, if class A has an aggregation relationship with class B, does class A own the lifetime of class B?

<p>No, class A does not own the lifetime of class B. Class B can exist independently. (B)</p> Signup and view all the answers

What is the primary purpose of the super() keyword in Java?

<p>To call a superclass constructor or access superclass members from a subclass. (A)</p> Signup and view all the answers

In object-oriented programming, what does 'runtime polymorphism' generally refer to?

<p>The ability to determine the type of an object at runtime and call the appropriate method. (B)</p> Signup and view all the answers

What is the difference between Zero or One (0..1) and Zero to Many (0..*) in UML multiplicities?

<p>0..1 means the relation is optional with at most one instance whereas 0..* means the relation is optional with no upper limit on instances. (B)</p> Signup and view all the answers

In aggregation, if an object A contains a reference to object B, what happens to object B when object A is destroyed?

<p>Object B continues to exist independently. (C)</p> Signup and view all the answers

Given two classes, Vehicle and Engine, where a Vehicle must have an Engine to function, and the Engine is created as part of the Vehicle creation, which relationship is best represented here?

<p>Composition (C)</p> Signup and view all the answers

Which is an accurate characteristic of method overloading (compile-time polymorphism)?

<p>Methods must have the same name but different parameter lists (number, type, or order of parameters). (B)</p> Signup and view all the answers

Given a class Animal and a subclass Bird, which statement correctly describes their relationship?

<p><code>Bird</code> IS-A <code>Animal</code> (A)</p> Signup and view all the answers

What does the term 'lifecycle dependency' refer to in the context of composition and aggregation?

<p>The relationship of one class to another in terms of their creation and destruction. (A)</p> Signup and view all the answers

Which relationship signifies a stronger coupling?

<p>Composition (A)</p> Signup and view all the answers

A Library can have multiple Book objects, but Book objects can exist without a Library. What relationship does this illustrate?

<p>Aggregation (A)</p> Signup and view all the answers

In a UML class diagram, what is the symbol for composition?

<p>A filled diamond (C)</p> Signup and view all the answers

What is the significance of polymorphism for real-world applications?

<p>It permits you to perform the same action on many object types in a uniform way. (A)</p> Signup and view all the answers

You are designing a system where a Student must have a Name, and the Name is created and destroyed along with the Student. What type of relationship should you use?

<p>Composition (C)</p> Signup and view all the answers

Flashcards

What is Inheritance?

A relationship where a class is a specialized version of another. It promotes code reuse and establishes an "is-a-kind-of" hierarchy.

Define Method Overriding

A mechanism where a subclass provides a specific implementation of a method already defined in its superclass, allowing different classes to respond differently to the same method call.

What is Method Overloading?

Having multiple methods with the same name but different parameters. It allows a class to provide different ways to perform a similar operation.

What is Polymorphism?

The ability of an object to take on many forms. In practice, this means that a single method name can work with different types of objects.

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What is Composition?

A strong "whole-part" relationship where one class is made up of one or more objects of other classes. If the 'whole' is destroyed, the 'parts' are also destroyed.

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What is Aggregation?

A 'whole-part' relationship where one class contains a reference to another class, but both can exist independently. If the 'whole' is destroyed, the 'parts' can still exist.

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What is Multiplicity in UML?

Defines how many instances of one class can be associated with instances of another class in a relationship.

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What is Constructor chaining?

The process where constructor of a subclass automatically calls the constructor of it's superclass before executing its own.

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Study Notes

Object-Oriented Concepts

  • Object-oriented context in SDLC, object-oriented analysis, noun & verb analysis, CRC cards, & analysis classes

Learning Objectives

  • Understand relationships between classes, implement inheritance in Java, apply polymorphism, and identify/implement composition.

UML Notation

  • UML class notation includes the class name, attributes, and methods.

Class Relationships

  • Relationships are identified and categorized when drawing CRC cards.
  • Relationships include dependency, association, aggregation, composition, and inheritance.
  • Dependency is the weakest and Inheritance is the strongest class relationship.
  • "Uses" means objects of one class work briefly with objects of another class.
  • "Works with" means objects of one class work with objects of another class.
  • "Has a" means when one class owns but shares a reference to objects of another class.
  • "Is a" means when one class is a type of another class.
  • "Whole part relationships" means when the parts can not exist without the whole.

Inheritance

  • Inheritance, also known as Generalization, represents an "is-a-kind-of" relationship.
  • Inheritance defines a relationship between a general class (superclass/parent) and a specific class (subclass/child)
  • The subclass inherits properties/behaviors (attributes/methods) of the superclass.
  • Implemented using "extends" keyword in Java.
  • Represented graphically with an empty arrow pointing from subclass to superclass.
  • Super Class/Parent is the Employee, Sub Classes/Children are Manager and Developer in an example.
  • Children inherit properties/methods of their parent class.
  • The super-class is a generalization of the sub-class but the sub-class is a specialization of the super-class.
  • Attributes should be "protected" so the child class can inherit/access them.
  • Child classes are implemented using the "extends" keyword and declaring attributes as "private".
  • Define attributes specific to the subclass, automatically inheriting parent's attributes/methods.
  • Use "super()" to pass values for parent's attributes to its constructor.
  • Override methods to customize behavior in the subclass.

Constructor Chaining

  • Constructor chaining: a subclass constructor automatically calls its superclass constructor before executing its own body.

Method Overriding

  • Overriding occurs when a subclass provides a new version of a method already defined in its superclass.
  • The overridden method must have the same name, return type, and parameters as in the superclass.
  • Method overriding allows a child class to change the implementation of an inherited method.

Polymorphism

  • Polymorphism means "many forms," enabling a method or object to take different forms.
  • Java's polymorphism allows a single method name to work with various object types, improving code reusability.
  • Polymorphism facilitates code reusability, flexibility, and maintainability.
  • calculateSalary() in the Employee class can be overridden in subclasses.
  • Method execution depends on the specific object it is called on.

Types of Polymorphism

  • Compile-time polymorphism (method overloading) involves multiple methods with the same name but different parameters.
  • Runtime polymorphism (method overriding) occurs when a subclass provides a new method version from the parent class.
  • The program determines the method to execute during runtime.

Composition

  • Composition means a class is made up of one or more objects of other classes (whole-part relationship).
  • A strong form of relationship where one class contains an object of another as part of its attributes.
  • If the containing (whole) object is destroyed, the contained (part) object is also destroyed.
  • Implemented using instance variables that reference other objects.
  • Shown graphically with a filled diamond connected by a line, placed next to the whole (containing) class.
  • "Part cannot exist without Whole."
  • Is implemented using instance variables that reference other objects inside the class.

Aggregation

  • Aggregation represents a "whole-part" relationship where one class references another, but both exist independently.
  • It is a weaker relationship compared to composition with unfilled diamond notation.
  • If the whole (containing) object is destroyed, the part object continues to exist outside.
  • Implemented using instance variables that store references to other objects but those objects are created outside the class.
  • "Part can exist without Whole"

Key Differences Between Aggregation and Composition

  • Composition is a strong "part of" relationship where parts cannot exist independently.
  • Aggregation is a weaker "part of" relationship where parts can exist independently.

Multiplicity in UML

  • Multiplicity defines how many instances of a class can be associated with those of another in a relationship
  • Multiplicity specifies one-to-one, one-to-many, or many-to-many relationships in class diagrams.

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