Java Lesson 6: Collections — List and Map
Store groups of objects with ArrayList and HashMap/TreeMap, loop over them, merge totals by key, and use streams for sums.
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Java basics and working with files and spreadsheets.
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Java basics and working with files and spreadsheets.
📄 10 articles⬇️ 10 with practice files🕒 Updated 12 Oct 2026
🎓 Start here: Rust Course → 🎓 Start here: Java Course → 🎓 Start here: R Course →Java Streams for Beginners: filter, map and collect Explained
Java Streams for Beginners: filter, map and collect Explained
Java Streams let you process lists in a clear, declarative style. Learn filter, map, sorted, collect and groupingBy with a small sales example.
Read article →Java Lesson 8: Project — An Invoice Calculator
Java Lesson 8: Project — An Invoice Calculator
Bring it together: an Invoice class with validated lines, GST calculation, item summaries with a Map and formatted output, plus next steps (Maven, Apache…
Read article →Java Lesson 7: Exceptions and Files
Java Lesson 7: Exceptions and Files
Handle errors with try/catch/finally, throw meaningful exceptions, and read and write text files with java.nio.file.Files.
Read article →Java Lesson 5: Classes and Objects
Java Lesson 5: Classes and Objects
Model real things with classes: fields, constructors, methods, private data with public methods, and records for simple data.
Read article →Java Lesson 4: Methods
Java Lesson 4: Methods
Write static methods with parameters and return types, overloading, and keeping methods small and testable.
Read article →Java Lesson 3: Conditions and Loops
Java Lesson 3: Conditions and Loops
Use if/else, switch expressions, comparison and logical operators, for, enhanced for and while loops in Java.
Read article →Java Lesson 2: Variables and Types
Java Lesson 2: Variables and Types
Java’s static types: int, double, boolean, char and String, declaring variables, var, arithmetic and integer division, casting and printf formatting.
Read article →Java Lesson 1: Install the JDK and Run Hello World
Java Lesson 1: Install the JDK and Run Hello World
Install a JDK (Temurin or Oracle), check java -version, write and run Hello.java from the terminal and in VS Code or IntelliJ IDEA.
Read article →Read and Write Excel Files in Java with Apache POI
Read and Write Excel Files in Java with Apache POI
A beginner-friendly guide to reading and writing .xlsx files in Java using Apache POI — with complete, working examples and common pitfalls.
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