Object-Oriented Programming Fundamentals

Object-Oriented Programming (OOP)

• Class and Object:
  • A class is a blueprint for creating objects.
  • An object is an instance of a class.
• Inheritance:
  • A child class inherits properties and behavior from a parent class.
  • Single inheritance: a child class can inherit from one parent class.
  • Multilevel inheritance: a child class can inherit from a parent class that itself inherits from another parent class.
• Polymorphism:
  • Method overriding: a child class provides a different implementation of a method with the same signature as a parent class.
  • Method overloading: multiple methods with the same name but different parameters.
• Abstraction:
  • Abstract classes and interfaces define a blueprint for other classes to follow.
  • Abstract methods have no implementation and must be implemented by subclasses.
• Encapsulation:
  • Data hiding: variables and methods are encapsulated within a class, making them inaccessible from outside.
  • Access modifiers (public, private, protected) control access to class members.

Multithreading

• Threads:
  • A thread is a separate flow of execution within a program.
  • Threads can run concurrently, improving program responsiveness and performance.
• Thread Creation:
  • Extend the Thread class or implement the Runnable interface.
  • Use the start() method to start a thread.
• Thread Synchronization:
  • Synchronized methods and blocks ensure thread safety by locking access to shared resources.
  • wait() and notify() methods allow threads to communicate and coordinate.
• Deadlocks and Starvation:
  • Deadlocks: two or more threads are blocked, waiting for each other to release a resource.
  • Starvation: a thread is unable to access a resource due to other threads holding onto it.

Collections

• Types of Collections:
  • List: an ordered collection of elements (e.g., ArrayList, LinkedList).
  • Set: an unordered collection of unique elements (e.g., HashSet, TreeSet).
  • Map: a collection of key-value pairs (e.g., HashMap, TreeMap).
• Collection Interfaces:
  • Iterable: provides a way to iterate over a collection.
  • Collection: provides basic operations (e.g., add, remove, contains) for a collection.
  • List, Set, and Map interfaces extend Collection and provide additional methods.
• Common Collection Classes:
  • ArrayList: a resizable array-based implementation of List.
  • LinkedList: a linked list-based implementation of List.
  • HashMap: a hash-based implementation of Map.

Exception Handling

• Try-Catch Blocks:
  • try block: contains code that may throw an exception.
  • catch block: catches and handles an exception.
• Exception Types:
  • Checked exceptions: must be explicitly handled or declared (e.g., IOException).
  • Unchecked exceptions: do not need to be explicitly handled or declared (e.g., NullPointerException).
• Throwing and Rethrowing:
  • throw statement: throws an exception explicitly.
  • throws clause: declares that a method may throw an exception.
  • Rethrowing: re-throwing an exception from a catch block to propagate it up the call stack.
• finally Block:
  • A finally block is executed regardless of whether an exception is thrown or not.
  • Used for resource cleanup and releasing locks.

Object-Oriented Programming (OOP)

• A class is a blueprint for creating objects.
• An object is an instance of a class.

Inheritance

• A child class inherits properties and behavior from a parent class.
• Single inheritance: a child class can inherit from one parent class.
• Multilevel inheritance: a child class can inherit from a parent class that itself inherits from another parent class.

Polymorphism

• Method overriding: a child class provides a different implementation of a method with the same signature as a parent class.
• Method overloading: multiple methods with the same name but different parameters.

Abstraction

• Abstract classes and interfaces define a blueprint for other classes to follow.
• Abstract methods have no implementation and must be implemented by subclasses.

Encapsulation

• Data hiding: variables and methods are encapsulated within a class, making them inaccessible from outside.
• Access modifiers (public, private, protected) control access to class members.

Multithreading

• A thread is a separate flow of execution within a program.
• Threads can run concurrently, improving program responsiveness and performance.

Thread Creation

• Extend the Thread class or implement the Runnable interface.
• Use the start() method to start a thread.

Thread Synchronization

• Synchronized methods and blocks ensure thread safety by locking access to shared resources.
• wait() and notify() methods allow threads to communicate and coordinate.

Deadlocks and Starvation

• Deadlocks: two or more threads are blocked, waiting for each other to release a resource.
• Starvation: a thread is unable to access a resource due to other threads holding onto it.

Collections

• List: an ordered collection of elements (e.g., ArrayList, LinkedList).
• Set: an unordered collection of unique elements (e.g., HashSet, TreeSet).
• Map: a collection of key-value pairs (e.g., HashMap, TreeMap).

Collection Interfaces

• Iterable: provides a way to iterate over a collection.
• Collection: provides basic operations (e.g., add, remove, contains) for a collection.
• List, Set, and Map interfaces extend Collection and provide additional methods.

Common Collection Classes

• ArrayList: a resizable array-based implementation of List.
• LinkedList: a linked list-based implementation of List.
• HashMap: a hash-based implementation of Map.

Exception Handling

• try block: contains code that may throw an exception.
• catch block: catches and handles an exception.

Exception Types

• Checked exceptions: must be explicitly handled or declared (e.g., IOException).
• Unchecked exceptions: do not need to be explicitly handled or declared (e.g., NullPointerException).

Throwing and Rethrowing

• throw statement: throws an exception explicitly.
• throws clause: declares that a method may throw an exception.
• Rethrowing: re-throwing an exception from a catch block to propagate it up the call stack.

finally Block

• A finally block is executed regardless of whether an exception is thrown or not.
• Used for resource cleanup and releasing locks.