Lesson 6.4: Looping Through Hardware Arrays with for-each

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Technical Context

Complex robots often utilize four drivetrain motors or multiple identical sensors. Iterating through these components individually is inefficient; using a for..each loop with a hardware array allows the programmer to apply a single command (like BRAKE behavior) to every component simultaneously, reducing the risk of accidentally missing a port.

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Why for-each Loops Scale Better with More Hardware

A Java array is instantiated to hold a fixed number of SDK objects (e.g., DcMotor[] motors = new DcMotor[4]). The for..each syntax — for (Type variable : array) — provides a shortcut to access every object in that array without managing an index integer, ensuring every connected component receives the instruction in a clean, readable block.

Two things to remember:

• Arrays in Java are zero-indexed — the first element is at index 0.
• The variable type declared in the for..each header must match the type stored in the array.

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Annotated Code

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DcMotor;

@TeleOp(name="Array_Drive_Demo")
public class ArrayDriveDemo extends OpMode {

    // Array declaration — holds all four drivetrain motors
    DcMotor[] allMotors;

    private DcMotor leftFront, rightFront, leftBack, rightBack;

    @Override
    public void init() {
        leftFront  = hardwareMap.get(DcMotor.class, "left_front");
        rightFront = hardwareMap.get(DcMotor.class, "right_front");
        leftBack   = hardwareMap.get(DcMotor.class, "left_back");
        rightBack  = hardwareMap.get(DcMotor.class, "right_back");

        // Populate the array after mapping
        allMotors = new DcMotor[]{ leftFront, rightFront, leftBack, rightBack };

        // Apply BRAKE behavior to every motor in one loop
        for (DcMotor motor : allMotors) {
            motor.setZeroPowerBehavior(DcMotor.ZeroPowerBehavior.BRAKE);
        }
    }

    @Override
    public void loop() {
        // Stop all motors at once using the array
        for (DcMotor motor : allMotors) {
            motor.setPower(0.0);
        }
    }
}

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Fill-in-the-Blank Practice

1. To declare an array of DC motors, the syntax is DcMotor__________ motors;.
2. The index of the first element in any Java array is __________.
3. In a for..each loop, the variable type must __________ the type of the objects stored in the array.

Show answers

1. [] (e.g., DcMotor[] motors;)
2. 0
3. match

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Template Challenge

Robot Scenario: You have an array of four motors named drivetrain. Complete the logic to set the ZeroPowerBehavior to BRAKE for every motor in the array.

package org.firstinspires.ftc.teamcode;

import com.qualcomm.robotcore.eventloop.opmode.OpMode;
import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
import com.qualcomm.robotcore.hardware.DcMotor;

@TeleOp(name="Array_Brake_Challenge")
public class ArrayBrake extends OpMode {

    private DcMotor[] drivetrain;

    @Override
    public void init() {
        // Assume the array is already populated with 4 mapped motors here

        // INSERT CODE HERE: Use a for..each loop to iterate through 'drivetrain'
        {
            // INSERT CODE HERE: Set each motor's ZeroPowerBehavior to BRAKE
        }
    }

    @Override
    public void loop() {}
}

Show answer

for (DcMotor motor : drivetrain) {
    motor.setZeroPowerBehavior(DcMotor.ZeroPowerBehavior.BRAKE);
}

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