> For the complete documentation index, see [llms.txt](https://docs.cb21829.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cb21829.org/ftc-java-advanced-guide/finite-state-machines.md).

# Finite state machines

Finite state machines are one of the most useful patterns in FTC.

Instead of blocking through a whole routine, you define states and move between them a little each loop.

### The pattern with an enum

```java
import com.qualcomm.robotcore.util.ElapsedTime;

public enum LiftState {
    IDLE,
    EXTENDING,
    DUMPING,
    RETRACTING
}

LiftState liftState = LiftState.IDLE;
ElapsedTime liftTimer = new ElapsedTime();

switch (liftState) {
    case IDLE:
        if (gamepad1.a) {
            lift.setTargetPosition(LIFT_HIGH);
            lift.setMode(DcMotor.RunMode.RUN_TO_POSITION);
            lift.setPower(0.8);
            liftState = LiftState.EXTENDING;
        }
        break;

    case EXTENDING:
        if (!lift.isBusy()) {
            dumpServo.setPosition(DUMP_POS);
            liftTimer.reset();
            liftState = LiftState.DUMPING;
        }
        break;

    case DUMPING:
        if (liftTimer.seconds() > 1.0) {
            dumpServo.setPosition(STOW_POS);
            lift.setTargetPosition(0);
            liftState = LiftState.RETRACTING;
        }
        break;

    case RETRACTING:
        if (!lift.isBusy()) {
            liftState = LiftState.IDLE;
        }
        break;
}
```

### Why this beats blocking code

Each state does a quick check and returns. The rest of the loop keeps running, so drivetrain, other mechanisms, and telemetry keep updating too.

### Scaling up

* give each subsystem its own FSM
* use FSMs to drive autonomous routes
* move to command-based structure when the state logic becomes too large


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