Summary of Core Java concepts

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Here's a summary of Core Java concepts:

1. Java Basics

  • Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle). It is platform-independent thanks to the "Write Once, Run Anywhere" philosophy, using the Java Virtual Machine (JVM) to run code on different platforms.

  • Java syntax is similar to C++, but it simplifies memory management through automatic garbage collection and eliminates some complex features (like pointers).

2. Data Types

Java supports two categories of data types:

  • Primitive types: byte, short, int, long, float, double, char, boolean.
  • Reference types: Objects, arrays, and interfaces.

3. Control Flow

Java uses standard control structures like:

  • if-else, switch-case for conditional branching.
  • for, while, do-while for loops.

4. Object-Oriented Programming (OOP)

Java is an object-oriented language, meaning it follows the principles of OOP:

  • Encapsulation: Wrapping data (fields) and methods (functions) into a single unit called a class.
  • Abstraction: Hiding complex implementation details and showing only the essential features.
  • Inheritance: A class can inherit fields and methods from another class.
  • Polymorphism: Allows one interface to be used for a general class of actions (overloading and overriding methods).

5. Classes and Objects

  • Class: A blueprint for creating objects, which encapsulates data for the object and methods to manipulate that data.
  • Object: An instance of a class.
  • Constructor: A special method that is called when an object is created, used to initialize object state.

6. Methods and Variables

  • Method: A block of code that performs a specific task.
  • Variable: A container for storing data values.
    • Local variables are declared inside methods.
    • Instance variables are declared in classes but outside methods.
    • Static variables are shared among all instances of a class.

7. Inheritance

  • A class can extend another class, inheriting its fields and methods.
  • The super keyword is used to refer to the parent class.
  • Java supports single inheritance (a class can only extend one class).

8. Interfaces and Abstract Classes

  • Interface: Defines a contract that classes can implement. It contains abstract methods (methods without implementation) and constants.
  • Abstract class: A class that cannot be instantiated directly. It can have both abstract (without implementation) and concrete (with implementation) methods.

9. Exception Handling

Java uses try-catch blocks to handle exceptions:

  • try: Contains code that may throw an exception.
  • catch: Handles exceptions that arise in the try block.
  • finally: Used to run code after try-catch, regardless of whether an exception occurred.
  • throw and throws are used for throwing and declaring exceptions, respectively.

10. Collections Framework

The Java Collections Framework provides classes and interfaces for storing and manipulating data:

  • List (ArrayList, LinkedList) stores ordered collections.
  • Set (HashSet, TreeSet) stores unique elements.
  • Map (HashMap, TreeMap) stores key-value pairs.
  • Queue (PriorityQueue, LinkedList) stores elements in a FIFO order.

11. Generics

Generics allow you to write classes, interfaces, and methods that work with any type of data. They provide type safety and eliminate the need for casting.

12. Java I/O

Java provides several classes for input/output (I/O) operations:

  • File: Represents file and directory pathnames.
  • FileReader/FileWriter: For reading and writing text files.
  • BufferedReader/BufferedWriter: For efficient reading and writing of text.
  • ObjectInputStream/ObjectOutputStream: For reading and writing objects.

13. Concurrency

Java has built-in support for multi-threading and concurrency:

  • Thread class and Runnable interface are used for creating and managing threads.
  • Synchronization ensures that only one thread can access a resource at a time.

14. JVM and Garbage Collection

  • JVM: Executes Java bytecode and provides memory management, including garbage collection to automatically free memory used by objects that are no longer in use.
  • Heap: Memory area for dynamic object allocation.
  • Stack: Memory area for method calls and local variables.

15. Lambda Expressions and Functional Programming (Java 8+)

Java 8 introduced lambda expressions, allowing functional programming features:

  • Lambda expression: A shorthand for writing anonymous methods.
  • Stream API: Provides methods for working with collections in a functional style, such as map(), filter(), and reduce().

16. Java 9+ Features

  • Modules: Introduced in Java 9, allowing developers to organize code into modules.
  • var keyword (Java 10): Allows local variable type inference.
  • Records (Java 14): A special type of class to model immutable data objects.
  • Sealed Classes (Java 15): Restrict which classes can extend a given class.

17. Java Development Tools

  • JDK (Java Development Kit): Includes the tools necessary for developing Java applications.
  • JRE (Java Runtime Environment): Includes the JVM and libraries for running Java applications.
  • IDE: Tools like Eclipse, IntelliJ IDEA, and NetBeans are commonly used for Java development.

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