Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Java Java Objects Harnessing the Power of Objects Throwing Exceptions

Tim Blacquier
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Tim Blacquier
Full Stack JavaScript Techdegree Graduate 20,961 Points

I need help with throwing an exception for the challenge, I cannot figure out what I am doing wrong.

it keeps saying not to change the lapsDriven or barCount fields but I am not.

GoKart.java
class GoKart {
  public static final int MAX_BARS = 8;
  private String color;
  private int barCount;
  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) {
    lapsDriven += laps;
    barCount -= laps;
    if (barCount < laps) {
      throw  new IllegalArgumentException("!!!");
    }

  }
}

1 Answer

andren
andren
28,558 Points

It tells you that you should throw the exception before lapsDriven and barCount is changed. If you look at the drive method you'll see that the first two lines do indeed change those variables:

public void drive(int laps) {
  lapsDriven += laps; // This increases lapsDriven
  barCount -= laps; // This decreases barCount
  if (barCount < laps) {
    throw new IllegalArgumentException("!!!");
  }
}

Which means that to throw the exception before those variables change, you have to place your code at the top of the method. Like this:

public void drive(int laps) {
  if (barCount < laps) {
    throw new IllegalArgumentException("!!!");
  }
  lapsDriven += laps;
  barCount -= laps;
}

If you don't then lapsDriven and barCount would be changed even if there is not enough bars for a lap, which would defeat the point of throwing the exception.

Edit: Changed some of my wording.