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Java Java Objects Harnessing the Power of Objects Throwing Exceptions

Posted by James Kane
.a{fill-rule:evenodd;}techdegree
James Kane
Front End Web Development Techdegree Student 3,070 Points

HELP. Well past the 20 minute rule been at this for almost 90 minutes, can someone please tell me what im doing wrong :(

Any advice much appreciated

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;
    int fuelRemaining = barCount - lapsDriven;
    if (fuelRemaining < laps) {
      throw new IllegalArgumentException("Not enough fuel");
    }
  }
}

2 Answers

Steve Hunter
Steve Hunter
57,712 Points

Hi James,

You're nearly there!

You wan't to check if the number of laps being requested is greater than the value held in barCount. if it is, throw the exception, as you have done else do the maths piece.

Your method is "doing the maths" irrespective, so it'll allow barCount to become negative if laps is greater than it. That's what we're trying to protect against.

So, test whether laps is greater than barCount and if it is, throw the IllegalArgumentException - else deduct laps from barCount and increase lapsDriven by laps.

That all looks something like:

  public void drive(int laps) {
    if(laps > barCount){
      throw new IllegalArgumentException("Not enough bars!");
    } else {
      lapsDriven += laps;
      barCount -= laps;
    }
  }

Make sense?

Steve.

Steve Hunter
Steve Hunter
57,712 Points

You can omit the else part as the method will exit if the exception is thrown so it'll not run if that's the case. But, personally, I prefer it being there for improved readability. The code below is fine but it doesn't highlight the binary nature of the code as either the exception will be thrown or the maths bit will happen; never both. I think the addition of the else clause makes that far more obvious. 

  public void drive(int laps) {
    if(laps > barCount){
      throw new IllegalArgumentException("Not enough bars!");
    }
    lapsDriven += laps;
    barCount -= laps;
  }
James Kane
.a{fill-rule:evenodd;}techdegree
James Kane
Front End Web Development Techdegree Student 3,070 Points

Yes Steve thanks a lot man!

Suleyman Orazgulyyev
PLUS
Suleyman Orazgulyyev
Courses Plus Student 5,798 Points
Suleyman Orazgulyyev
Suleyman Orazgulyyev
Courses Plus Student 5,798 Points

Hey! So basically you have to check if the number of laps inputted is greater than the number of batteries. If it is, it means that there is not enough battery so you throw an exception. Here it is:

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