Java Object-oriented Programming & Exception Handling

Questions and Answers

What is the primary purpose of encapsulation in object-oriented programming?

To allow classes to inherit from one another

To enable method overloading and overriding

To bundle data and methods together within a class (correct)

To hide complex implementation details from users

Which keyword is used to indicate that a method might throw exceptions in Java?

try

catch

throw

throws (correct)

What is polymorphism in object-oriented programming?

The capability to perform an action in multiple ways (correct)

The ability to bundle data and methods together

A way of hiding implementation details

The mechanism for classes to inherit from one another

What defines checked exceptions in Java?

Exceptions that must be declared or caught Signup and view all the answers

What does the 'finally' block do in exception handling?

It runs code after try/catch, regardless of the result Signup and view all the answers

What is an abstract class in Java?

A class that cannot be instantiated and may contain abstract methods Signup and view all the answers

Which access modifier restricts access to the same package and subclasses?

protected Signup and view all the answers

In exception handling, what does the 'catch' block do?

It handles specific exceptions that may occur Signup and view all the answers

Which of the following scenarios best describes method overriding?

Redefining a method in a subclass with the same name and parameters Signup and view all the answers

How do you explicitly throw an exception in Java?

Using the throw keyword Signup and view all the answers

Study Notes

Java: Object-oriented Programming

Core Concepts:
- Classes and Objects:
  - Class: Blueprint for creating objects (contains fields and methods).
  - Object: Instance of a class.
- Encapsulation:
  - Bundling data (attributes) and methods (functions) together.
  - Access modifiers: private, public, protected, and default.
- Inheritance:
  - Mechanism where one class inherits properties and methods from another.
  - Enables code reusability.
- Polymorphism:
  - Ability to perform a single action in different ways.
  - Achieved through method overloading (same method name, different parameters) and method overriding (subclass provides a specific implementation).
- Abstraction:
  - Hiding complex implementation details and showing only essential features.
  - Achieved using abstract classes and interfaces.

Java: Exception Handling

Definition:
- Mechanism to handle runtime errors, ensuring the normal flow of execution.
Key Components:
- Exception: An event that disrupts the normal execution of a program.
- Error: Issues that cannot be handled by the program (e.g., OutOfMemoryError).
Exception Handling Keywords:
- try: Block of code that may throw an exception.
- catch: Block that handles exceptions thrown by the try block.
- finally: Block that executes code after try/catch, regardless of whether an exception occurred.
- throw: Used to explicitly throw an exception.
- throws: Declaration in a method signature that indicates a method might throw exceptions.
Common Exceptions:
- Checked Exceptions: Must be declared or caught (e.g., IOException).
- Unchecked Exceptions: Do not need to be declared (e.g., NullPointerException, ArrayIndexOutOfBoundsException).
Best Practices:
- Catch specific exceptions rather than generic ones.
- Clean up resources in the finally block.
- Use custom exceptions for better error handling in application-specific scenarios.

Java: Object-oriented Programming

Classes and Objects:
- A class serves as a blueprint for object creation, encompassing fields (attributes) and methods (functions).
- An object is a concrete instance derived from a class.
Encapsulation:
- Combines data (attributes) and methods into a single unit.
- Access modifiers control visibility:
  - private: Accessible only within the class.
  - public: Accessible from anywhere.
  - protected: Accessible within the class and subclasses.
  - Default: Accessible within the same package.
Inheritance:
- Allows one class to inherit properties and methods from another class.
- Promotes code reusability and establishes a relationship between classes.
Polymorphism:
- Enables a single action to take different forms.
- Method overloading allows using the same method name with different parameters.
- Method overriding allows a subclass to provide a specific implementation of a method from its superclass.
Abstraction:
- Conceals complex implementation details, exposing only the essential features.
- Implemented through abstract classes (cannot be instantiated) and interfaces (define methods that must be implemented).

Java: Exception Handling

Definition:
- A mechanism designed to manage runtime errors, ensuring that the normal flow of execution is maintained.
Key Components:
- Exception: An event that interrupts normal program execution.
- Error: Serious issues that are typically not recoverable by the application, such as OutOfMemoryError.
Exception Handling Keywords:
- try: Code block that may throw an exception.
- catch: Block that catches and handles exceptions thrown by the try block.
- finally: Block that executes after try/catch, regardless of whether an exception was thrown.
- throw: Used to explicitly trigger an exception.
- throws: Indicates in the method signature that a method may throw exceptions.
Common Exceptions:
- Checked Exceptions: Must be declared or caught in the code (e.g., IOException).
- Unchecked Exceptions: Do not require declaration (e.g., NullPointerException, ArrayIndexOutOfBoundsException).
Best Practices:
- Focus on catching specific exceptions to improve handling.
- Utilize the finally block to clean up resources.
- Implement custom exceptions for more effective error handling tailored to application-specific scenarios.

Description

Test your knowledge on core concepts of Java, including classes, objects, encapsulation, inheritance, polymorphism, and abstraction. Additionally, explore exception handling mechanisms to manage runtime errors effectively. Perfect for students looking to enhance their Java programming skills.