Summer · Week 5 of 8

OOP — Classes & Objects

The most important week in this course. Everything in FRC robot code is a class.

Why this matters: Every subsystem on 2974's robot is a class. Drivetrain.java, Shooter.java, Coral.java, Finger.java — all classes. Understanding this week means you can read and write real robot code.

Classes vs Objects

A class is a blueprint. An object is one specific thing built from that blueprint. You write the class once, then create as many objects as you need — each with their own independent data.

java — class definition

public class Motor {
    // Instance variables — each Motor object gets its own copy
    private int     id;
    private double  speed;
    private boolean isInverted;

    // Constructor — runs when you do "new Motor(...)"
    public Motor(int id, boolean isInverted) {
        this.id         = id;
        this.isInverted = isInverted;
        this.speed      = 0.0;
    }

    public void setSpeed(double speed) {
        this.speed = isInverted ? -speed : speed;
    }

    public double getSpeed() { return speed; }
}

java — creating and using objects

Motor leftMotor  = new Motor(1, false);
Motor rightMotor = new Motor(2, true); // inverted

leftMotor.setSpeed(0.5);
rightMotor.setSpeed(0.5);

System.out.println(leftMotor.getSpeed());  // 0.5
System.out.println(rightMotor.getSpeed()); // -0.5 — inverted!

Instance Variables

Data each object stores

Each object gets its own copy. leftMotor.id and rightMotor.id are completely separate.

Constructor

Runs on new

Same name as class. No return type. Sets the initial state of the object.

this

Refers to current object

When a parameter and instance variable share a name, this.speed means the instance variable.

Encapsulation

Private + getters/setters

Keep data private, expose it through methods that can validate input. Prevents accidental corruption.

Access Modifiers

Modifier	Who can access it	When to use
public	Anyone, anywhere	Methods you want others to call
private	Only inside this class	Instance variables (almost always)
protected	This class + subclasses	When you plan for inheritance

Live Class Builder

Type field declarations and watch the class generate

Class name

Fields (comma sep, e.g. int id, double speed)

Fill in the Blanks

// Declare a private double field
double motorSpeed;

// Constructor for class Intake taking int motorID
public (int motorID) { }

// Create a new Motor with id=3, inverted=false
Motor m =

Knowledge Check

Coding Challenge

⚡

Build an Intake Class

Write a real FRC subsystem class from scratch

Write an Intake class with private fields int motorID, double speed, boolean isRunning. Constructor takes motorID, sets speed=0 and isRunning=false. Methods: start(double speed), stop(), isRunning(), getSpeed(). Then create two objects and test them.

← Previous Week 4 — Arrays & Methods Next → Week 6 — Inheritance & Polymorphism