How do you throw the exception before changing fields? Keep getting an error message on GoKart exceptions exercise

Question

I believe that my code is correct here (it looks near identical to the exercise we had done just before) but I can't get it to execute properly. I've tried everything I can think of...

"Make sure you throw the exception before you change the barCount and lapsDriven fields."

Thanks!

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(int laps) {

    int newLapsDriven = lapsDriven += laps;
    int newBarCount = barCount -= laps;   
    if (newBarCount < 0) {
     throw new IllegalArgumentException("Not enough juice!"); 
    }

    lapsDriven = newLapsDriven;
    barCount = newBarCount;
  }

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

Answer 1 · 2017-09-28T14:43:21Z

September 28, 2017 2:43pm

The problem is that you use the += and -= operator in your first two lines. Those operators takes the variable on the left and adds/subtracts the value on the right to it. If your goal is just to add or subtract the values together without modifying the variable involved in the computation then you should just use the normal + and - operator.

Like this:

 public void drive(int laps) {
  int newLapsDriven = lapsDriven + laps; // += replaced with +
  int newBarCount = barCount - laps; // -= replaced with -
  if (newBarCount < 0) {
    throw new IllegalArgumentException("Not enough juice!"); 
  }

  lapsDriven = newLapsDriven;
  barCount = newBarCount;
}

It's worth mentining though that while that will work you didn't really need to create the newLapsDriven and newBarCount variables in the first place to solve this challenge. If you use laps > barCount as the condition for your if statement then you could have kept the original code that was in the drive method intact.

Like this:

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

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Luke Strama

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How do you throw the exception before changing fields? Keep getting an error message on GoKart exceptions exercise

1 Answer

andren

andren

Luke Strama

Luke Strama