Mental Model: Pomodoro Timer TUI in Java

Timers are state machines with a clock. That’s the mental model.

State Machine First

This Pomodoro has a small set of states:

phase: focus or break
running: true or false
remaining seconds
completed focus sessions

Every command and every tick should update these predictably.

Two Loops in One Program

The app alternates between:

command mode (paused): read and handle user input
tick mode (running): sleep 1 second, decrement, maybe transition

If you keep these modes clear, the code stays easy to reason about.

Transition Logic Is the Heart

tick() is where correctness lives.

decrement remaining time
when it hits zero, switch phase
reset remaining seconds for the new phase
increment session count after focus completes

This is classic finite-state-machine behavior.

Java-Specific Insight

Java’s explicit fields make timer state very legible.

you can inspect all important fields quickly
helper methods (resetCurrentPhase, statusLine) isolate concerns
Thread.sleep + interrupt handling teaches real runtime basics

It’s simple, but it’s real systems thinking.

Debugging by Invariants

Keep a few invariants in your head:

remaining seconds should never go negative for long
phase changes only at zero
session count increases only after focus phase

When behavior is weird, check invariants first.

Next Feature Ideas

auto-start next phase toggle
long break every 4 sessions
daily history saved to file

Add features without breaking the state machine model, and you’ll build robust timer apps.