Interfaces, Packages, and Code Organization

Keep code navigable as the robot grows.

Module 7: Command Patterns and Code OrganizationAdvanced

In this lesson, you will:

01Organize files by responsibility.
02Use interfaces for shared capabilities.
03Avoid circular dependencies.

Concept narrative

Code organization is architecture students can see in the file tree. Packages should make ownership obvious: hardware, subsystems, commands, opmodes, vision, drive, and util.

This lesson should be read as a robotics lesson first and a programming lesson second. The code matters because it lets the team create repeatable behavior under match pressure. Students should slow down long enough to name the inputs, outputs, assumptions, and safety limits before they touch the robot.

Robot mental model

A clean package structure helps new programmers find the right file. Interfaces are useful when different mechanisms expose the same capability, such as resettable or telemetry-reporting behavior.

A good mental model gives the team a shared language. When a driver, builder, and programmer can point to the same behavior and use the same words, debugging gets calmer and code review becomes useful instead of personal.

Implementation walkthrough

Create packages before the codebase becomes chaotic. Move one utility into util, one mechanism into subsystem, and one action into command. Keep imports readable.

Keep the implementation staged. First create the smallest version that compiles. Then add telemetry that proves it is running. Then connect one hardware device or one decision. Finally, repeat the test from a cold init so the team knows it was not a lucky hot reload.

PackageExample.javaJava

public interface Resettable {
    void reset();
}

public class ArmSubsystem implements Resettable {
    @Override public void reset() { updateState(ArmState.SAFE); }
}

Common mistakes and debugging

If files import across every package, ownership is muddy. If an interface has only one implementation and no clear purpose, it may be unnecessary. Keep organization simple but intentional.

Use the five-value debugging habit: input, state, target, measurement, output. If one of those values is missing, add it before rewriting logic. The goal is to make the robot tell the truth about what it thinks is happening.

Checkpoint

Package names match responsibilities.
Interfaces have a real reason.
New files have obvious homes.

Reflection check

Check your understanding before moving on.

What is the most important habit in Interfaces, Packages, and Code Organization?

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References

Learn Java for FTCFTC-focused Java book and exercises by Alan G. Smith.FIRST FTC DocsOfficial SDK, Robot Controller, and programming reference.Game Manual 0FTC community reference for programming, controls, and robot design.