IllegalArgumentException

class Example {

  public static void main(String[] args) {
    GoKart kart = new GoKart("purple");
    if (kart.isBatteryEmpty()) {
      System.out.println("The battery is empty");
    }
    try {
      kart.drive(42);
      System.out.println("Battery Down");
    } catch (IllegalArgumentException iae) {
      System.out.println("Whoa there");
      System.out.printf("The error was %s \n", 
                        iae.getMessage());
    }
  }
}

class GoKart {
  public static final int MAX_BARS = 8;
  private int barCount;
  private String color;
  private int lapsDriven;

  public GoKart(String color) {
    this.color = color;
  }

  public String getColor() {
    return color;
  }

  public void charge() {
    barCount = MAX_BARS;
  }

  public boolean isBatteryEmpty() {
    return barCount == 0;
  }

  public boolean isFullyCharged() {
    return MAX_BARS == barCount;
  }

  public void drive() {
    drive(1);
  }

  public void drive(int laps) {
    int newLaps = laps - barCount;
    if (newLaps < barCount) {
      throw new IllegalArgumentException("Not enough battery remain");
    }
    newLaps = barCount;
  }

}