Unit 3 Mastery Quiz: Java Variables

I. Conceptual Questions

1. Precision Engineering: Why must the variable used to store a DcMotor's power level be declared as a double rather than an int?

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The setPower() method requires a value between -1.0 and 1.0. Because int is a 32-bit primitive that only stores whole numbers, it would truncate any decimal power (e.g., 0.5 would become 0), rendering precise velocity control impossible.

2. Class vs. Primitive: Technically, why is the String datatype capitalized in Java while boolean and double are lowercase?

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boolean and double are primitive datatypes built directly into the language. String is a class defined in the Java library, and by engineering convention, all class names must utilize PascalCase.

3. State Capture: What is the technical advantage of assigning a sensor's state (e.g., touchSensor.getState()) to a boolean variable at the start of the loop() method?

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This captures a "snapshot" of the hardware's physical state at a specific point in time. This prevents logic errors where a sensor's state might change mid-cycle, leading to inconsistent decision-making within a single execution of the loop().

4. Configuration Management: Why is it considered a professional "Best Practice" to store hardware names (like "left_drive") in a String variable at the class level instead of passing a literal string directly into hardwareMap.get()?

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Storing names in variables creates a "single source of truth." If a hardware port name is changed in the Robot Controller configuration, the programmer only needs to update one variable rather than searching for every instance of that literal string throughout the project.

5. Computational Accuracy: When calculating motor rotations with the formula motor.getCurrentPosition() / ticksPerRotation, why should ticksPerRotation be stored as a double even if the value is a whole number?

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In Java, dividing an int by an int results in integer division, where the remainder is discarded (e.g., 5 / 2 = 2). By using a double, Java "promotes" the calculation, ensuring the result is a precise decimal value.

II. Debug the Code

The following code is intended to read an analog Potentiometer and scale its voltage to a motor power level. Identify and fix the 2 errors.

package org.firstinspires.ftc.teamcode;

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

@TeleOp(name="Variable_Debug")
public class VariableDebug extends OpMode {

    DcMotor lift;
    AnalogInput pot;

    int targetPower = 0.75

    @Override
    public void init() {
        lift = hardwareMap.get(DcMotor.class, "lift");
        pot  = hardwareMap.get(AnalogInput.class, "pot");
    }

    @Override
    public void loop() {
        // Logic: Set motor power based on the variable
        lift.setPower(targetPower);
    }
}

Show answers

Error 1 — Syntax Error: The declaration int targetPower = 0.75 is missing a semicolon (;) at the end of the statement. Furthermore, assigning a decimal value (0.75) to an int will cause a compiler error because an int cannot hold fractional data.

Error 2 — Logic Error: The variable targetPower is declared as an int. Even if the syntax were corrected, any value assigned to it that is less than 1 (like 0.75) would be truncated to 0. The motor would never move because setPower() would only ever receive a 0. The variable must be declared as a double:

double targetPower = 0.75;

Ready to move on?

I. Conceptual Questions​

II. Debug the Code​

I. Conceptual Questions

II. Debug the Code