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

Posted by Francis Agyemang-Duah
Francis Agyemang-Duah
Courses Plus Student 365 Points

Adding logic to a method

How do I add logic to a method so that it throws an IllegalArgumentException?

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) {
    int requestedAmount = lapsDriven + laps;
    if(MAX_BARS < 0) {
      throw new IllegalArgumentException("Too many laps");
    }
    lapsDriven = requestedAmount;
  }
}

2 Answers

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

The "throw" itself is correct, but:

  • the test should check the argument against the available energy
  • the test (and throw) should be done first in the method
  • the other code that will otherwise be done should not be modified
Francis Agyemang-Duah
PLUS
Francis Agyemang-Duah
Courses Plus Student 365 Points
Francis Agyemang-Duah
Francis Agyemang-Duah
Courses Plus Student 365 Points

public void drive(int laps) { int requestedAmount = barCount - laps; if(requestedAmount < 0) { throw new IllegalArgumentException("Battery too low"); } barCount = requestedAmount; } }

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

The original code body lines need to remain as they were to be done after the test (for those cases where the "throw" is not done).