Inner class in Java

package anote;

import java.util.ArrayList;
public class Main {
    public static void main(String[] args) {

        Gearbox mcLaren = new Gearbox(6);
        Gearbox.Gear first = mcLaren.new Gear(1, 12.3);
        System.out.println(first.driveSpeed(1000));
    }
}

class Gearbox {
    private ArrayList<Gear> gears;
    private int maxGears;
    private int gearNumber = 0;

    public Gearbox(int maxGears) {
        this.maxGears = maxGears;
        this.gears = new ArrayList<>();
        Gear neutral = new Gear(0, 0.0);
        this.gears.add(neutral);
    }

    public class Gear {
        private int gearNumber;
        private double ratio;
    
        public Gear (int gearNumber, double ratio){
            this.gearNumber = gearNumber;
            this.ratio = ratio;
        }
        public double driveSpeed(int revs){
            return revs * ( this.ratio);
        }
    }
}