Java Fundamentals

What Java Is and Your First Program

Java runs on billions of devices — Android phones, bank servers, point-of-sale systems. Write and run your first program and see how Java code becomes a running app.

Variables and Data Types

Java wants to know what kind of value every variable holds. Learn the core types, how to convert between them, and why that strictness saves you from bugs.

Decisions and Loops

Programs become useful when they make decisions and repeat work. Master if/else, switch, and the for, while and for-each loops.

Reading Input and Formatting Output

Programs get interesting when they respond to people. Read keyboard input with Scanner, validate it, and print tidy, formatted results.

Methods: Reusable Blocks of Code

Stop repeating yourself. Write methods with parameters and return values, and learn overloading and how Java passes values.

Arrays and Working with Text

Store many values in one variable and clean, split and format text — skills you will use in every app form.

Classes and Objects

Object-oriented programming is the heart of Java — and of Android. Model real things as classes with fields, constructors and methods.

Inheritance, Interfaces and Polymorphism

Share behaviour between classes and write code that works with many types at once — exactly how Android's Activity and listener classes work.

Enums and Records: Modelling Data Cleanly

Replace magic strings with enums that the compiler checks, and replace boilerplate classes with one-line records. Cleaner models mean fewer bugs.

Collections: ArrayList and HashMap

Arrays have a fixed size; real apps need lists that grow and fast lookups by key. Meet ArrayList, HashMap and generics.

Generics: Code That Works for Any Type

Write one class or method that safely works with Strings, numbers or your own types. Generics are why List<String> exists, and every Android library uses them.

Streams and Lambdas: Processing Data in One Line

Filter, transform, group and total collections the modern way. Streams turn ten-line loops into readable pipelines, and lambdas are how Android handles clicks.

Handling Errors with Exceptions

Apps meet bad input, missing files and lost connections. Catch problems gracefully instead of crashing.

Files and Dates

Save and load data from files so it survives after the program closes, and handle dates and times correctly: due dates, ages and receipts.

Packages, Gradle and Testing with JUnit

Leave the single-file playground: organise code into packages, pull in libraries with Gradle, and prove your code works with automated tests.

Mini Project: A Console Shop

Put it all together — classes, collections, methods and exceptions — in a small shop program. This is the thinking you will reuse in your first Android app.