使用对象的float属性的compareTo（）方法。如何使用，为什么？

我班上的代码，我不太了解。我在互联网上读到compareTo（）方法用于比较字符串和字符串，对象用于字符串，但是在我的代码中，它用于比较浮点数和字符串，我猜呢！您能否说明下面的代码中如何使用compareTo（）方法，以及为什么在我们的案例中使用它？

package ro.ase.acs.classes;

import ro.ase.acs.interfaces.Mobility;
//Comparable is a generic interface; click add unimplemented methods ; the method will appear at the end of the class
public final class Car extends Vehicle implements Mobility, Cloneable,Comparable<Car> {
    public static final int maxNbOfKm = 1_000_000;//it is static, in order to acces it use .
    private EngineType engineType;
    private float speed;

    public Car() {
        super();
        engineType = EngineType.gas;
        speed = 0;
    }

    public Car(String _name, EngineType _engineType, float _speed) {
        super(_name, true);
        engineType = _engineType;
        speed = _speed;
    }

    @Override
    public void Start() {
        System.out.println("The " + engineType.toString() +
                " car has started!");
    }

    @Override
    public void Stop() {
        System.out.println("The " + engineType.toString() +
                " car has stopped!");
    }

    @Override
    public void DisplaySpeed() {
        System.out.println(String.format("The %s car runs with %f km/h",
                engineType.toString(), speed));
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("The car named ");
        sb.append(name);
        sb.append(" has a(n) ");
        sb.append(engineType.toString());
        sb.append(" engine and is running with ");
        sb.append(speed);
        sb.append(" km/h");
        return sb.toString();
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        Car c = (Car)super.clone();
        c.engineType = engineType;
        c.speed = speed;
        return c;
    }

    @Override
    public boolean equals(Object obj) {
        if(!(obj instanceof Car)) {
            return false;
        }
        else {
            Car c = (Car)obj;
            return name.equals(c.name);
        }
    }

@Override
public int hashCode()
{
    return 31*name.hashCode()+13*(HasEngine()?1:0)+7*engineType.hashCode()+(int)speed*100;
}


    public enum EngineType { gas, diesel, electric, hybrid }



    @Override
    public int compareTo(Car o) {
        if(speed==o.speed)
        {return 0;}
        else if (speed>o.speed)
        {
            return 1;
        }
        else
        {return -1;}




    }

//  public final int hashCode() {
    //  return engineType.hashCode();
//  };
}