The Capstone Brief

Time to assemble. The capstone is a personal transaction ledger: a text-persisted record of money in and money out. Nothing here is new - that's the point. It composes:

• records (Module 9) - an immutable Transaction with a compact constructor validating itself;
• collections + streams (Modules 10, 12) - a List<Transaction> queried with pipelines;
• defensive parsing (Module 11) - every loaded line survives a try/catch gauntlet;
• file persistence (this module) - save and load through Files.writeString/readString;
• testing discipline (Module 13) - the grading tests are the bar, and you've written your own all course.

The format you're building

One transaction per line, four fields, |-separated:

2026-01-15|coffee|CASH_OUT|4.50
2026-01-16|salary|CASH_IN|2500.00

CASH_IN adds to the balance, CASH_OUT subtracts. That's the entire schema - the complexity lives in handling it well.

How the capstone is graded

You get requirements, tests, and hints - not a tutorial. The four test blocks each fail until the matching behavior exists: validation, round-trip persistence, filtering/summary queries, and balance arithmetic with defensive guards. Build the Ledger methods one test block at a time; when all four pass, the capstone is done and so is the course.

Where you could go next

Java Intermediate would take you from this: generics you write (not just read), inheritance hierarchies that pay rent, interfaces as contracts, builder patterns, and the first real concurrency. The ledger is the foundation those courses assume - finish it, understand every line, and you've earned the title this course promised: someone who can write Java.