Introduction to Java

Introduction to Java (Module 1)

• Java is a high-level, object-oriented programming language.
• Sun Microsystems, now owned by Oracle, developed Java in 1995.
• Java is widely used for building platform-independent applications.
• The Java "White Paper" buzzwords include simple, object-oriented, distributed, robust, secure, architecture-neutral, portable, interpreted, high-performance, multithreaded, and dynamic.
• Key features include platform independence, object-oriented design, robustness and security, multithreading, memory management, rich API and library support, high performance, and support for distributed computing and networking.
• JVM (Java Virtual Machine) runs Java bytecode.
• JRE (Java Runtime Environment) includes the JVM and necessary libraries for running Java applications.
• JDK (Java Development Kit) includes the JRE and development tools like compilers and debuggers.

Variables and Data Types (Module 2)

• A variable in Java is a named memory location used to store data.
• String stores text, such as "Hello".
• int stores integers (whole numbers), without decimals, such as 123 or -123.
• float stores floating point numbers, with decimals, such as 19.99 or -19.99.
• char stores single characters, such as 'a' or 'B'.
• boolean stores values with two states: true or false.
• Implicit Type Casting (Widening Conversion) automatically converts a smaller data type into a larger data type.
• Explicit Type Casting (Narrowing Conversion) requires manually converting larger data types into smaller data types.

Control Flow in Java (Module 3)

• The if...else statement allows for conditional execution of code blocks.
• A simple if statement executes code only if the condition is true.
• The if...else if...else statement allows for checking multiple conditions.
• A nested if...else statement is an if...else statement inside another if...else statement.
• A while loop executes as long as the condition is true
• A for loop is used when the number of iterations is known.
• A do...while loop executes at least once, then continues if the statement is true.
• An enhanced for loop is used for iterating over arrays or collections.
• A break statement ends the ongoing process.
• A continue statement is used to control the flow of code by skipping the rest of the loop body for the current iteration.
• A switch statement is a control structure that lets one choose one block of code to run out of many options, based on the value of a variable.

Introduction to Object-Oriented Programming (Module 4)

• Object-Oriented Programming (OOP) is a programming paradigm focused on designing software using objects.
• OOP is used due to Modularity, Reusability, Scalability, Encapsulation, and Polymorphism
• Classes are blueprints or templates for creating objects.
• Objects are instances of a class that contains real values for attributes and can perform defined behaviors.
• Classes in OOP have a State, Behavior and a Constructor
• A constructor is a block of code that gets executed when an object of a class is created.
• A Default Constructor (No-Arg Constructor), does not have any arguments
• Parameterized Constructors have arguments/parameters
• Copy Constructor allows you to copy each of the variables of one object into another object.
• Constructor Overloading means a class has more than one constructor

Ways to Initialize Objects in Java

• Instance Initialization Block
• Static Initialization Block

This and Super in Constructors

• The keyword this() is used in constructors to call another constructor in the same class
• The keyword super() is used in constructors to call the constructor of the superclass

Encapsulation and Abstraction in Java (Module 5)

• Encapsulation focuses on how something should get done, abstraction focuses on what should get done.
• Access modifiers are keywords that define the accessibility of a class and its members, including default (package private), private (visible within the class only), protected (visible within the package or all subclasses), and public (visible everywhere).
• Data hiding is a concept that involves encapsulating data within a class and restricting access to certain components using access modifiers.
• Code reusability is the practice of using existing code (components, modules, or libraries) in new projects or applications.
• An abstract class cannot be instantiated.
• Abstract classes should be inherited by other classes.
• Abstract classes can have both abstract and regular methods.
• An abstract method is a method without a body (no implementation).
• Abstract methods must be overridden in a subclass.
• An interface is like a contract; it contains method declarations (no body).
• A class that implements an interface must define all its methods
• Use the interface Keyword
• Abstract Classes provide a common base for a group of related classes, allowing for code reuse and enforcing a specific structure.
• An interface define a contract or set of behaviors that classes must implement, ensuring they provide certain functionality.