Java Object-oriented Programming Concepts

Java: Study Notes

Object-oriented Programming

• Core Principles:
  • Encapsulation: Bundling data (attributes) and methods (functions) that operate on the data in a single unit (class).
  • Abstraction: Hiding complex reality while exposing only the necessary parts. Achieved using interfaces and abstract classes.
  • Inheritance: Mechanism to create new classes based on existing ones, promoting code reusability.
  • Polymorphism: Ability of a variable, function, or object to take on multiple forms, primarily through method overriding and overloading.

Inheritance

• Types:
  • Single Inheritance: A class inherits from one superclass.
  • Multilevel Inheritance: A class inherits from a superclass, which also serves as a superclass for another class.
  • Hierarchical Inheritance: Multiple classes inherit from a single superclass.
  • Multiple Inheritance: Not supported directly; can be achieved through interfaces.
• Keywords:
  • extends: Used to inherit a class.
  • super: Refers to the superclass, used to access superclass methods and constructors.

Abstraction

• Abstract Classes:
  • Cannot be instantiated.
  • Can contain abstract methods (without a body) and concrete methods (with a body).
• Interfaces:
  • A reference type in Java, similar to a class, but can only contain method signatures and final static variables.
  • A class implements an interface using the implements keyword.

Exception Handling

• Purpose: Mechanism to handle runtime errors, ensuring the normal flow of the application.
• Keywords:
  • try: Block of code where exceptions may occur.
  • catch: Block that handles exceptions.
  • finally: Block that executes after try/catch, regardless of if an exception occurred.
  • throw: Used to explicitly throw an exception.
  • throws: Declares that a method may throw exceptions.
• Types of Exceptions:
  • Checked Exceptions: Must be handled or declared (e.g., IOException).
  • Unchecked Exceptions: Do not need to be explicitly handled (e.g., NullPointerException).

File Handling

• Classes:
  • File: Represents the file or directory path.
  • FileReader: Used to read data from a file.
  • FileWriter: Used to write data to a file.
  • BufferedReader and BufferedWriter: For efficient reading and writing of text data.
• Common Methods:
  • read(): Reads data from a file.
  • write(): Writes data to a file.
  • close(): Closes the file stream to free resources.
• File Operations:
  • Creating, reading, writing, and deleting files.
  • Handling paths using Path and Paths classes in Java NIO for better file operations.

Object-oriented Programming

• Encapsulation combines data and methods within a single class, enhancing data hiding.
• Abstraction simplifies complex systems by exposing only necessary interfaces and functionalities through abstract classes and interfaces.
• Inheritance allows new classes to derive properties and behaviors from existing classes, fostering code reusability.
• Polymorphism enables entities to take on multiple forms, primarily through method overriding and overloading.

Inheritance

• Single inheritance involves a class deriving from one superclass.
• Multilevel inheritance allows a class to inherit from a superclass, which can serve as a superclass for another class.
• Hierarchical inheritance features multiple subclasses inheriting from one superclass.
• Multiple inheritance is not directly supported in Java but can be achieved using interfaces.
• The extends keyword is used to inherit a class, while super is used to access methods and constructors of the superclass.

Abstraction

• Abstract classes cannot be instantiated and may contain both abstract methods (without implementation) and concrete methods (with implementation).
• Interfaces serve as a reference type and can only contain method signatures and final static variables; classes implement interfaces using the implements keyword.

Exception Handling

• Exception handling ensures the application can manage runtime errors without crashing, maintaining normal flow.
• The try block contains code that may throw exceptions, while the catch block handles those exceptions.
• The finally block executes regardless of exception occurrence, providing a clean-up mechanism.
• The throw keyword is used to explicitly raise an exception, and throws indicates that a method may throw exceptions during execution.
• Checked exceptions need explicit handling or declaration, while unchecked exceptions do not require mandatory handling.

File Handling

• The File class represents file and directory paths.
• FileReader is utilized for reading data from files, whereas FileWriter is used for writing data to files.
• BufferedReader and BufferedWriter facilitate efficient text data reading and writing.
• Common file operations include creation, reading, writing, and deletion of files.
• The Path and Paths classes in Java NIO enhance file operations and path handling.

Test your knowledge on the core principles of object-oriented programming in Java, including encapsulation, abstraction, inheritance, and polymorphism. This quiz also covers the various types of inheritance models in Java. Dive into the key concepts that underpin effective Java programming.