☕ Java

What Java is, why it is popular, how the JVM works, and how to run your first Java program.

Declare, initialize and use variables in Java. Primitive types, default values and variable scope.

Rules for naming identifiers, list of reserved keywords, and Java naming conventions.

Primitive vs reference types, sizes, defaults, and type casting rules in Java.

Arithmetic, relational, logical, assignment, bitwise and ternary operators — with precedence rules.

if, if-else, else-if ladder, nested if, and switch statements in Java.

for, while, do-while and enhanced for-each loops with break and continue.

Declare, initialize and access single-dimensional and 2D arrays in Java.

Define, call and overload methods. Parameters, return types and scope.

Define a class, create objects, use constructors and access instance members — the heart of OOP.

Work with text using String methods, compare strings the right way, and build text efficiently with StringBuilder.

Go deeper into constructors: your own no-arg constructor, overloading, chaining with this(), copy constructors and validation.

Use static for data and methods that belong to the whole class, and final for values, methods and classes that must not change.

Reuse code by building a child class on top of a parent class with extends, call the parent with super, and override methods.

One name, many forms: compile-time polymorphism with overloading, run-time polymorphism with overriding, upcasting and dynamic method dispatch.

Use abstract classes and interfaces to say what a class must do while leaving how it does it to the subclasses.

Protect an object's data with private fields, getters and setters, and control who can see what with access modifiers and packages.

Stop programs from crashing on bad input: try, catch and finally, checked vs unchecked exceptions, throw, throws and your own exception classes.

Write methods that call themselves: base case and recursive case, factorial, Fibonacci, the call stack and StackOverflowError.

Store data in lists that grow as needed with ArrayList, sort them with Collections, and look values up by key with HashMap.