Comparable Interface

public class Car implements Comparable {

    private String model;
    private double price;
    private int maxSpeed;

    public Car(String model, double price, int maxSpeed) {
        this.model = model;
        this.price = price;
        this.maxSpeed = maxSpeed;
    }

    public String getModel() {
        return model;
    }
    public void setModel(String model) {
        this.model = model;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    public int getMaxSpeed() {
        return maxSpeed;
    }
    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    @Override
    public String toString() {
        return "Car [model=" + model + ", price=" + price + ", maxSpeed=" + maxSpeed + "]";
    }

    @Override
    public int compareTo(Object obj) {
        Car other = (Car)obj;
        if (this.maxSpeed > other.maxSpeed) {
            return -1;
        } else if (this.maxSpeed < other.maxSpeed) {
            return 1;
        }
        return 0;
    }

}

import java.util.ArrayList;
import java.util.Collections;

public class Program {
    public static void main(String[] args) {
        ArrayList<Car> cars = new ArrayList<Car>();

        cars.add(new Car("Mercedes-Benz", 50055.3, 230));
        cars.add(new Car("Lada Niva", 5005.3, 330));
        cars.add(new Car("Opel Astra", 15005.3, 200));

        Collections.sort(cars);

        for (Car c : cars) {
            System.out.println(c);
        }
    }
}