Using Constructors

The next program uses the constructor to initialize a car rather than setting the fields directly.

class CarTest7 {

  public static void main(String args[]) {
    
    Car c = new Car("New York A45 636", 123.45);
    
    System.out.println(c.getLicensePlate() + " is moving at " + c.getSpeed() + 
     " kilometers per hour.");

    for (int i = 0; i < 15; i++) {
      c.accelerate(10.0);
      System.out.println(c.getLicensePlate() + " is moving at " + c.getSpeed() 
       + " kilometers per hour.");
    }

  }
    
}

You no longer need to know about the fields licensePlate, speed and maxSpeed. All you need to know is how to construct a new car and how to print it.

You may ask whether the setLicensePlate() method is still needed since it's now set in a constructor. The general answer to this question depends on the use to which the Car class is to be put. The specific question is whether a car's license plate may need to be changed after the Car object is created.

Some classes may not change after they're created; or, if they do change, they'll represent a different object. The most common such class is String. You cannot change a string's data. You can only create a new String object. Such objects are called immutable.