Java Object-Oriented Programming

Object-Oriented Programming in Java

Key Concepts

• Class: A blueprint or template that defines the properties and behaviors of an object.
• Object: An instance of a class, which has its own set of attributes (data) and methods (functions).
• Inheritance: A mechanism that allows one class to inherit the properties and behaviors of another class.
• Polymorphism: The ability of an object to take on multiple forms, depending on the context in which it is used.
• Abstraction: The concept of showing only the necessary information to the outside world while hiding the internal details.
• Encapsulation: The concept of bundling data and methods that operate on that data within a single unit (class).

Classes and Objects

• A class is defined using the class keyword.
• A class can have multiple constructors, which are used to initialize objects.
• An object is created using the new keyword, followed by the constructor.
• Classes can have instance variables (data members) and instance methods (functions).

Inheritance

• A child class inherits the properties and behaviors of a parent class using the extends keyword.
• A child class can override the methods of a parent class.
• A child class can also add new methods or variables.

Polymorphism

• Method overriding: When a child class provides a different implementation of a method that is already defined in its parent class.
• Method overloading: When multiple methods with the same name can be defined with different parameter lists.
• Runtime polymorphism: When the actual method to be called is determined at runtime, rather than at compile time.

Abstraction and Encapsulation

• Abstract classes: Classes that cannot be instantiated and are used as a base class for other classes.
• Abstract methods: Methods that are declared but not implemented in an abstract class.
• Interfaces: Abstract classes that define a contract that must be implemented by any class that implements it.
• Access modifiers: Public, private, protected, and default access modifiers are used to control access to classes, variables, and methods.

Benefits of OOP

• Code reuse: Through inheritance and polymorphism, code can be reused in multiple contexts.
• Modularity: Code is organized into modular units (classes) that can be easily maintained and updated.
• Easier maintenance: Changes to the code can be made at a single location, without affecting other parts of the program.

Object-Oriented Programming in Java

Key Concepts

• Class: A blueprint or template that defines properties and behaviors of an object.
• Object: An instance of a class, with its own set of attributes (data) and methods (functions).
• Inheritance: A mechanism that allows one class to inherit properties and behaviors of another class.
• Polymorphism: Ability of an object to take on multiple forms, depending on the context.
• Abstraction: Concept of showing only necessary information to the outside world while hiding internal details.
• Encapsulation: Bundling data and methods that operate on that data within a single unit (class).

Classes and Objects

• A class is defined using the class keyword.
• A class can have multiple constructors, used to initialize objects.
• An object is created using the new keyword, followed by the constructor.
• Classes can have instance variables (data members) and instance methods (functions).

Inheritance

• A child class inherits properties and behaviors of a parent class using the extends keyword.
• A child class can override methods of a parent class.
• A child class can also add new methods or variables.

Polymorphism

• Method overriding: A child class provides a different implementation of a method already defined in its parent class.
• Method overloading: Multiple methods with the same name can be defined with different parameter lists.
• Runtime polymorphism: Actual method to be called is determined at runtime, rather than at compile time.

Abstraction and Encapsulation

• Abstract classes: Classes that cannot be instantiated and are used as a base class for other classes.
• Abstract methods: Methods that are declared but not implemented in an abstract class.
• Interfaces: Abstract classes that define a contract that must be implemented by any class that implements it.
• Access modifiers: Public, private, protected, and default access modifiers control access to classes, variables, and methods.

Benefits of OOP

• Code reuse: Through inheritance and polymorphism, code can be reused in multiple contexts.
• Modularity: Code is organized into modular units (classes) that can be easily maintained and updated.
• Easier maintenance: Changes to the code can be made at a single location, without affecting other parts of the program.

Java Basics

Variables and Data Types

• Java has two main categories of data types: primitive and reference
• Primitive Data Types:
  • Integers: byte (e.g., 1), short (e.g., 10), int (e.g., 100), long (e.g., 1000)
  • Floating-point numbers: float (e.g., 1.0), double (e.g., 2.0)
  • Characters: char (e.g., 'A')
  • Boolean: boolean (e.g., true/false)
• Reference Data Types:
  • Arrays (e.g., int[] myArray = {1, 2, 3})
  • Classes and Objects (e.g., Person person = new Person("John", 25))

Operators

• Arithmetic Operators:
  • Addition: a + b
  • Subtraction: a - b
  • Multiplication: a * b
  • Division: a / b
  • Modulus: a % b
• Comparison Operators:
  • Equal: a == b
  • Not Equal: a != b
  • Greater Than: a > b
  • Less Than: a < b