Java

What Java is, why "write once, run anywhere" still matters, and where the language fits today.

What the JDK actually contains, and writing the "Hello, World" every Java program starts from.

How javac and java turn source code into bytecode and then into a running program.

Declaring variables in a statically typed language, and the eight primitive types Java builds everything on top of.

Converting between Java's numeric types safely, and where implicit conversion stops and explicit casting begins.

Arithmetic, comparison, logical, and assignment operators, plus the gotchas around integer division and equality.

Branching logic in Java, from simple conditionals to the modern switch expression.

Java's three loop forms, when to reach for each one, and how break and continue control them.

Fixed-size, typed collections — how to declare, fill, and iterate over Java arrays, and what happens when you go out of bounds.

Packaging behavior into reusable methods — parameters, return types, and the static keyword.

Defining multiple methods with the same name but different parameters, and how Java decides which one to call.

The blueprint-and-instance model at the heart of Java — defining a class and creating objects from it.

Initializing objects reliably with constructors, overloaded constructors, and constructor chaining.

Sharing behavior between classes with extends, method overriding, and the role of super.

Two ways to define a contract without full implementation, and how to choose between them.

Controlling visibility with public, private, and protected, and why hiding state behind getters and setters matters.

Java's built-in family of resizable data structures — List, Set, and Map — and when to reach for each.

Writing type-safe, reusable classes and methods with generics, and why they replaced raw Object-based collections.

Java's functional-style tools for processing collections declaratively instead of with manual loops.

Handling runtime errors gracefully with try/catch/finally, and the important difference between checked and unchecked exceptions.

What Spring Boot, Quarkus, and Jakarta EE each bring to the table, and how to pick between them.

A closing checklist of habits that separate solid, maintainable Java from code that merely compiles.