Create a Comparable class to compare and sort objects in Java

/*from w  ww  .j  a  va2 s  . c om*/
import java.util.Arrays;

public class Main {
  public static void main(String[] args) {
    Car car1 = new Car("A",  5000);
    Car car2 = new Car("B", 5000);
    Car car3 = new Car("C", 4000);

    System.out.println("Car 1 equals Car 2: " + car1.compareTo(car2));
    System.out.println("Car 1 equals Car 3: " + car1.compareTo(car3));
    System.out.println("Car 2 equals Car 3: " + car2.compareTo(car3));

    Car[] carArray = new Car[] { car1, car2, car3 };
    Arrays.sort(carArray);

    for (Car car : carArray)
      System.out.println(car.toString());
  }
}

class Car implements Comparable {
  private String make;

  private int mileage;

  public Car(String make, int mileage) {
    this.make = make;
    this.mileage = mileage;
  }

  public int compareTo(Object obj) {
    if (obj instanceof Car) {
      Car car = (Car) obj;
      if (this.mileage > car.getMileage())
        return 1;
      else if (this.mileage < car.getMileage())
        return -1;
    }
    return 0;
  }

  public int getMileage() {
    return mileage;
  }

  public String toString() {
    StringBuffer buffer = new StringBuffer();
    buffer.append("Make: " + make + ",Mileage: " + mileage);
    return buffer.toString();
  }
}