Object-Oriented Programming (OOP) in Java

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Questions and Answers

What is the most restrictive access modifier in object-oriented programming?

  • no modifier
  • protected
  • private (correct)
  • public

Which access modifier allows access from all classes within the same package?

  • public
  • protected
  • private
  • no modifier (correct)

When should the protected modifier be preferred over the private modifier?

  • When a method is fully public.
  • When subclasses need direct access to an internal method or attribute. (correct)
  • When attributes are not intended to be accessed by subclasses.
  • When the attribute should be entirely hidden from other classes.

What does the public access modifier imply for methods and attributes?

<p>They are accessible from the current class and all other classes. (A)</p> Signup and view all the answers

Which access modifier should generally be used as the default choice for attributes?

<p>private (D)</p> Signup and view all the answers

In which scenario might you choose not to use the private modifier?

<p>When subclasses require direct access to internal methods. (B)</p> Signup and view all the answers

What is one of the main reasons for avoiding public access modifiers on attributes?

<p>It makes the attributes part of the public API. (D)</p> Signup and view all the answers

Which statement is accurate regarding the no modifier access level?

<p>It allows access to all classes within the same package. (C)</p> Signup and view all the answers

What does a class represent in Java?

<p>A collection of properties and methods. (A)</p> Signup and view all the answers

Which concept in Object Oriented Programming refers to bundling data and behavior together?

<p>Encapsulation (D)</p> Signup and view all the answers

What defines the properties and methods that an object created from a class can have?

<p>The class itself. (A)</p> Signup and view all the answers

What is an object in Java?

<p>An offspring of a class. (D)</p> Signup and view all the answers

Why is Object Oriented Programming beneficial for software development?

<p>It increases performance and maintainability. (D)</p> Signup and view all the answers

What term is used to describe the methods and properties contained within a class?

<p>Members of the class (D)</p> Signup and view all the answers

Which of the following statements about classes is true?

<p>A class serves as a template for creating objects. (A)</p> Signup and view all the answers

In the context of Java, what is the primary purpose of a constructor?

<p>To initialize objects when they are created. (C)</p> Signup and view all the answers

What does encapsulation primarily ensure in object-oriented programming?

<p>Binding of object state and behavior together (B)</p> Signup and view all the answers

Which of the following is the correct purpose of using private instance variables in a class?

<p>To restrict direct access and ensure data hiding (A)</p> Signup and view all the answers

What is a consequence of using public getter and setter methods?

<p>They allow isolation of class implementation from external code (B)</p> Signup and view all the answers

Why is it important to document public methods in a class?

<p>To aid other developers in understanding usage and constraints (D)</p> Signup and view all the answers

What does the term 'data hiding' refer to in encapsulation?

<p>Restricting access to data members through visibility modifiers (C)</p> Signup and view all the answers

Which method names are commonly used in encapsulation for accessing private fields?

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

What could happen if a method is poorly documented and publicly available?

<p>It may lead to misuse or unintended effects in the application (A)</p> Signup and view all the answers

How does encapsulation contribute to maintaining the integrity of an object's state?

<p>By restricting access to its internal representation (B)</p> Signup and view all the answers

What is encapsulation primarily known for?

<p>Data hiding from outside classes (A)</p> Signup and view all the answers

Which of the following accurately describes a constructor?

<p>It is called when an instance of the class is created. (C)</p> Signup and view all the answers

What distinguishes a parameterized constructor from a default constructor?

<p>It requires input parameters. (A)</p> Signup and view all the answers

Which of the following statements is TRUE about packages in Java?

<p>Packages help to organize classes and prevent naming conflicts. (D)</p> Signup and view all the answers

What does the import java.util.Scanner; statement achieve?

<p>It imports the Scanner class from the built-in util package. (A)</p> Signup and view all the answers

Which of the following is NOT a component of a package in Java?

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

What is one major advantage of using packages in Java?

<p>Reusability of code components (A)</p> Signup and view all the answers

What is a user-defined package in Java?

<p>A custom package that is created by the programmer (A)</p> Signup and view all the answers

How can name conflicts be avoided when using classes in Java?

<p>By placing classes with the same name in different packages (B)</p> Signup and view all the answers

Which of the following is NOT a reason to use packages in Java?

<p>To increase the speed of code execution (C)</p> Signup and view all the answers

How would you import a class named 'Calculator' from a package named 'letmecalculate'?

<p>import letmecalculate.Calculator; (B)</p> Signup and view all the answers

What type of package includes predefined classes, such as 'java.io' and 'java.lang'?

<p>Built-in packages (B)</p> Signup and view all the answers

In Java, which statement about the package declaration is correct?

<p>There can only be one package declaration per class. (A)</p> Signup and view all the answers

What is an example of a method that could be found in a class named 'Calculator'?

<p>public int add(int a, int b) (D)</p> Signup and view all the answers

What is the primary role of a constructor in a class?

<p>To initialize new objects of the class (B)</p> Signup and view all the answers

What is encapsulation primarily responsible for in object-oriented programming?

<p>Hiding the internal workings of a class from the outside (A)</p> Signup and view all the answers

Which method can be defined to allow reading the value of a private field in Java?

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

What distinguishes a parameterized constructor from a default constructor?

<p>The default constructor does not accept parameters while a parameterized one does (C)</p> Signup and view all the answers

Which of the following is NOT an advantage of using packages in Java?

<p>Increases visibility of internal classes (D)</p> Signup and view all the answers

In the context of the provided class example, what is the correct statement about the default constructor?

<p>It defines specific values for instance variables (A)</p> Signup and view all the answers

What encapsulation technique keeps class details hidden from users?

<p>Utilizing access modifiers (B)</p> Signup and view all the answers

What does the statement 'import java.util.Scanner;' indicate?

<p>It accesses utilities in the Scanner class for user input (D)</p> Signup and view all the answers

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Study Notes

Object-Oriented Programming (OOP) in Java

  • OOP is a software development approach organizing software as objects containing data and behavior.
  • OOP improves software performance, maintainability, and development by structuring projects around objects.
  • Key concept: combining data and behavior within objects (encapsulation).

Classes in Java

  • A class is a blueprint defining the structure and behavior of objects.
  • It specifies properties (data and functions) for its objects, acting as a template for object creation.
  • Classes define methods and data, controlling access using access specifiers.

Objects in Java

  • Objects are fundamental entities representing real-world entities with specific behavior, identity, and data.
  • In Java, objects are instances of classes, inheriting properties and methods.
  • Methods define an object's responses to interactions with other objects.

Access Modifiers

  • private: Most restrictive; accessible only within the same class. Default for attributes and internal methods unless inheritance requires broader access.
  • No modifier (package-private): Accessible within the same class and other classes in the same package.
  • protected: Accessible within the same class, within the same package, and by subclasses in other packages. Useful for internal methods overridden by subclasses.
  • public: Least restrictive; accessible from any class. Use cautiously, mainly for well-documented and robust methods.

Encapsulation

  • Binds object state (fields) and behavior (methods) together. Creating a class inherently involves encapsulation.
  • Hides implementation details from users. Private data members are only accessible from within the class itself.
  • Public getter and setter methods provide controlled access to private data, achieving data hiding.

Constructors in Java

  • A constructor is similar to a method, but it's not a method: It has the same name as the class and does not return a value.
  • Used to create objects (instances) of a class. Example: MyClass obj = new MyClass(); calls the default constructor.
  • Parametrized constructors accept arguments when creating an object.

Packages in Java

  • Packages organize classes, interfaces, and other packages.
  • Two types: built-in (e.g., java.util.Scanner) and user-defined.
  • Advantages: Reusability, better organization, avoidance of naming conflicts.

User-Defined Packages

  • Created by declaring the package name as the first statement in a Java file (e.g., package letmecalculate;).
  • Used via import statements (e.g., import letmecalculate.Calculator;).
  • A class can have only one package declaration.

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Week 3 - OOP Concepts.pdf

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