Mechanism Games

Java from absolute zero to under-the-hood internals — you don't read the mechanism, you enact it.
Play a unit. Then explain it — in your own words.

Phase 0 — Start from zero

01Your first program
Robots, println, the semicolon, and how Java actually runsPLAY 02Variables
Boxes with names — and why = means "store", never "equals"PLAY 03Data types & casting
Why 7 / 2 is 3 — and how to make it 3.5PLAY 04Operators
%, precedence, and 17 pizza slices for 5 friendsPLAY 05Strings
"1" + 1 = "11", counting from zero, and your first crashPLAY 06User input
Scanner, the pause, and what "abc" does to nextInt()PLAY 07Booleans & comparisons
true/false as values; &&, ||, ! — and = vs ==PLAY 08If / else
Forks in the road — and why ladder order mattersPLAY 09Switch
The dispatcher — and the famous missing-break trapPLAY 10While loops
Repeat until — and surviving your first infinite loopPLAY 11For loops
init; condition; update — and the off-by-one of all timePLAY 12Arrays
A numbered shelf, index 0, and the out-of-bounds crashPLAY 13Methods
Machines with inputs and outputs — defining runs nothingPLAY 14Scope & recursion
Evaporating boxes, the call stack, and StackOverflowErrorPLAY

Phase 1 — Objects

15Classes & objects
Blueprints, houses — and two leashes on one dogPLAY 16Constructors & this
Birth certificates, and the vanishing default constructorPLAY 17Encapsulation
private walls, guarded doors, unbreakable objectsPLAY 18Inheritance & super
is-a, shared members, and the two-stage birthPLAY 19Polymorphism & overriding
The runtime type decides — and @Override saves youPLAY 20Abstraction & interfaces
Incomplete blueprints and pure contractsPLAY 21static & final
What the class itself owns — and main() fully explainedPLAY 22Packages & the API
Folders, imports, and Java's giant free libraryPLAY 23Enums & inner classes
Types where invalid values are impossiblePLAY 24equals, hashCode & toString
Why == lies about objects — and how HashMaps lose themPLAY

Phase 2+ — Data, exceptions, modern Java, internals

Progress is saved in your browser only (localStorage — no accounts, no tracking).
Built with the enact-the-mechanism method: every step is something you do, not something you read.