Java: OOP Concepts

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Questions and Answers

In object-oriented programming, what is the primary purpose of encapsulation?

  • To enable a class to inherit properties from another class.
  • To bundle data and methods, hiding internal implementation details. (correct)
  • To allow objects of different classes to respond to the same method call.
  • To define a contract for classes, specifying methods to be implemented.

Which concept allows objects of different classes to respond to the same method call in their own way?

  • Polymorphism (correct)
  • Inheritance
  • Encapsulation
  • Abstraction

In Java, what is the purpose of an interface?

  • To inherit properties from another class.
  • To encapsulate data and methods.
  • To define a contract for classes to implement. (correct)
  • To create objects directly.

What distinguishes an abstract class from a concrete class in Java?

<p>Abstract classes cannot be instantiated and may contain abstract methods. (A)</p> Signup and view all the answers

Which access modifier provides the highest level of encapsulation in Java?

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

What is the primary benefit of using inheritance in object-oriented programming?

<p>It promotes code reuse and establishes hierarchical relationships. (A)</p> Signup and view all the answers

How does method overriding contribute to polymorphism?

<p>It allows a subclass to provide a specific implementation of a method that is already defined in its superclass. (A)</p> Signup and view all the answers

Which statement about static fields is correct?

<p>Only one copy of a static field exists, regardless of the number of objects created. (B)</p> Signup and view all the answers

What is the purpose of the finally block in exception handling?

<p>To specify the code that must be executed regardless of whether an exception occurred. (C)</p> Signup and view all the answers

Which Java class is commonly used to read data from a text file?

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

Which of the following principles is NOT directly facilitated by object-oriented programming?

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

What is the significance of using generics in Java?

<p>They provide type safety and eliminate the need for casting. (B)</p> Signup and view all the answers

If a class declares a method as protected, which classes can access this method?

<p>Classes within the same package and subclasses of this class. (D)</p> Signup and view all the answers

How can you prevent a class from being instantiated?

<p>Both B and C. (D)</p> Signup and view all the answers

What is method overloading?

<p>Creating multiple methods with the same name but different signatures in the same class. (A)</p> Signup and view all the answers

Which of the following statements is true about interfaces in Java?

<p>Interfaces can extend multiple interfaces. (D)</p> Signup and view all the answers

What is the purpose of a try-catch block?

<p>To handle runtime errors gracefully. (B)</p> Signup and view all the answers

In the context of object-oriented programming, what describes an object's characteristics?

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

Which of the following control structures allows code execution based on a condition?

<p><code>if-else</code> statement (C)</p> Signup and view all the answers

What is the significance of the super keyword in Java?

<p>It is used to call a method of the superclass. (D)</p> Signup and view all the answers

Flashcards

What are Classes?

Blueprints for creating objects; defines the attributes and behaviors of objects.

What are Objects?

Instances of classes, possessing states (attributes) and behaviors (methods).

What is Inheritance?

A mechanism where a class inherits properties and methods from another class, promoting code reuse and hierarchical relationships.

What is Polymorphism?

Allows objects of different classes to respond to the same method call in their own way, achieved through method overriding and overloading.

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What is Encapsulation?

Bundling data and methods that operate on that data within a class, hiding internal implementation details from the outside world through access modifiers.

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What is an Interface?

Defines a contract for classes to implement, specifying methods that must be implemented.

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What is an Abstract Class?

Cannot be instantiated and may contain abstract methods (methods without implementation).

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What are Static Fields?

Class-level variables shared among all instances of a class; only one copy exists, regardless of the number of objects created.

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What is Exception Handling?

A mechanism to handle runtime errors gracefully using try-catch blocks to catch and handle exceptions, and finally block to execute code regardless of exceptions.

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What are Generics?

Enable type parameters to be used in classes, interfaces, and methods, providing type safety and eliminating the need for casting.

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Study Notes

  • Java utilizes object-oriented programming.

Classes and Objects

  • Classes are blueprints for creating objects.
  • Objects are instances of classes.
  • Objects have states (attributes) and behaviors (methods).

Inheritance

  • Inheritance enables a class to inherit properties and methods from another class.
  • Promotes code reuse and establishes hierarchical relationships between classes.

Polymorphism

  • Polymorphism allows objects of different classes to respond to the same method call in their own way.
  • Achieved through method overriding (runtime polymorphism) and method overloading (compile time polymorphism).

Encapsulation

  • Encapsulation involves bundling data (attributes) and methods that operate on that data within a class.
  • Hides the internal implementation details from the outside world.
  • Achieved through access modifiers (private, protected, public).

Interfaces and Abstract Classes

  • Interfaces define a contract for classes to implement, specifying methods that must be implemented.
  • Abstract classes cannot be instantiated and may contain abstract methods (methods without implementation).

Control Structures

  • Selection structures (e.g., if-else statements, switch statements) allow code execution based on conditions.
  • Repetition structures (e.g., for loops, while loops) enable code to be executed repeatedly.

Static Fields

  • Static fields are class-level variables shared among all instances of a class.
  • Only one copy of a static field exists, regardless of the number of objects created.

Exception Handling

  • Exception handling is a mechanism to handle runtime errors gracefully.
  • try-catch blocks are used to catch and handle exceptions.
  • finally block is used to execute code that must be executed regardless of whether an exception occurred.

Text Files

  • Text files store data as plain text.
  • Java provides classes like BufferedReader and BufferedWriter to read from and write to text files.

Generics

  • Generics enable type parameters to be used in classes, interfaces, and methods.
  • Provide type safety and eliminate the need for casting.

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