Introduction to Java Programming

• Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible.
• It is a general-purpose programming language intended to let application developers write once, run anywhere (WORA), meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.
• Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture.
• The syntax of Java is similar to C and C++, but it has fewer low-level facilities than either of them.
• As of 2019, Java was one of the most popular programming languages in use, particularly for client-server web applications, with a reported 9 million developers.
• Java SE 8, 11 and 17 are among the long-term support (LTS) versions.

Java Fundamentals

• Object-Oriented Programming (OOP) is a programming paradigm based on the concept of "objects", which contain data, in the form of fields (often known as attributes or properties), and code, in the form of procedures (often known as methods).
• The four pillars of OOP are: Abstraction, Encapsulation, Inheritance, and Polymorphism.
• Abstraction involves simplifying complex reality by modeling classes appropriate to the problem, and working at the most appropriate level of inheritance for a given aspect of the problem.
• Encapsulation hides the internal state and requires all interaction to be performed through an object's methods, protecting the integrity of the object.
• Inheritance enables new objects to take on the properties of existing objects.
• Polymorphism allows objects of different classes to respond to the same method call in their own way.
• Key Java concepts include: Classes and Objects, Data Types, Variables, Operators, Control Flow Statements (if-else, loops), Arrays, Strings, Methods, and Exception Handling.
• Classes are blueprints for creating objects, defining their attributes and methods.
• Objects are instances of classes, representing real-world entities.
• Primitive data types in Java include: int, float, double, boolean, char, byte, short, and long.
• Variables are named storage locations that hold data values.
• Operators perform operations on variables and values.
• Control flow statements control the order in which code is executed.
• Arrays are collections of elements of the same data type.
• Strings represent sequences of characters.
• Methods are blocks of code that perform specific tasks.
• Exception handling is a mechanism to handle runtime errors gracefully.
• The Java Class Library (JCL) is a set of pre-written classes and interfaces that are available for use in Java programs. It provides a wide range of functionalities, such as input/output, networking, and graphical user interface (GUI) development.

Spring Framework

• Spring is an open-source application framework and inversion of control container for the Java platform.
• The framework's core features can be used by any Java application, but there are extensions for building web applications on top of the Java EE platform.
• Spring provides infrastructure support for developing Java applications.
• Key features include: Dependency Injection (DI), Aspect-Oriented Programming (AOP), Data Access, Transaction Management, and Model-View-Controller (MVC) framework.
• Dependency Injection (DI) is a design pattern in which objects receive other objects that they depend on.
• DI promotes loose coupling and testability.
• Aspect-Oriented Programming (AOP) enables modularization of cross-cutting concerns such as logging and security.
• Spring simplifies database interactions through its Data Access Object (DAO) support.
• Spring supports declarative transaction management, simplifying transaction handling.
• Spring MVC provides a framework for building web applications based on the Model-View-Controller design pattern.
• The Spring ecosystem includes projects like Spring Boot, Spring Data, Spring Security etc.
• Spring Boot simplifies the setup and configuration of Spring applications.
• Spring Data simplifies database access using repositories.
• Spring Security provides authentication and authorization support.
• The Inversion of Control (IoC) container is a core feature of the Spring Framework.
• The IoC container manages the lifecycle of beans (objects) and injects dependencies into them.
• Inversion of Control (IoC) principles invert the flow of control as compared to traditional programming.
• The key principles of IoC are: dependency injection (DI), dependency lookup.
• With dependency injection, dependencies are provided to the objects as constructor arguments, factory method arguments, or properties set on the object instance after it is constructed.
• With dependency lookup, components can request dependencies from a container. Using dependency lookup is less common.
• Bean scopes define the lifecycle and visibility of beans managed by the Spring container.
• Common bean scopes include: singleton, prototype, request, session, and application.

Spring MVC

• Spring MVC is a module of the Spring Framework that provides a Model-View-Controller (MVC) architecture for building web applications.
• The Model encapsulates the application data and business logic.
• The View is responsible for rendering the model data to the user.
• The Controller handles user requests and updates the model.
• Key components of Spring MVC include: DispatcherServlet, Controllers, View Resolvers, and Handler Mappings.
• The DispatcherServlet is the front controller that handles all incoming requests.
• Controllers handle user requests and return a logical view name.
• View Resolvers map logical view names to actual view implementations.
• Handler Mappings map incoming requests to specific controller methods.
• Annotations like @Controller, @RequestMapping, @GetMapping, @PostMapping, @PathVariable, and @RequestParam are used to define controllers and handle requests.
• View technologies like JSP, Thymeleaf, and FreeMarker can be used to render the view.
• Spring MVC supports data binding, validation, and internationalization.
• Interceptors can be used to intercept requests before and after they are handled by the controller.

Hibernate ORM

• Hibernate is an object-relational mapping (ORM) framework for Java.
• It provides a framework for mapping an object-oriented domain model to a relational database.
• Hibernate simplifies database interactions by automating the mapping of Java objects to database tables.
• Key features include: Object-Relational Mapping (ORM), Session Management, Transaction Management, and Query Language (HQL).
• ORM maps Java objects to database tables and vice versa.
• Hibernate automatically generates SQL queries based on object relationships.
• Hibernate provides APIs for managing database sessions and transactions.
• Hibernate Query Language (HQL) is an object-oriented query language similar to SQL.
• Hibernate supports various database dialects.
• Hibernate can be integrated with Spring for declarative transaction management.
• The Java Persistence API (JPA) is a Java standard for ORM frameworks.
• Hibernate is an implementation of the JPA specification.
• The main components of Hibernate are: Configuration, SessionFactory, Session, Transaction.
• The Configuration object is used to configure Hibernate settings.
• The SessionFactory is a factory for creating Session objects.
• The Session is the main interface for interacting with the database.
• The Transaction interface is used to manage database transactions.
• Annotations like @Entity, @Table, @Id, @GeneratedValue, @Column, @OneToMany, @ManyToOne are used to map Java classes to database tables.
• Hibernate supports different types of mappings, including: one-to-one, one-to-many, many-to-one, and many-to-many.
• Caching is an important feature of Hibernate that can improve application performance.
• Hibernate supports different levels of caching: first-level cache, second-level cache, and query cache.