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Java Java Objects Harnessing the Power of Objects Throwing Exceptions

What's wrong with my drive() code in this unit?

It says:

Make sure you throw a new IllegalArgumentException if the requested amount of laps would make the battery less than zero.

My code:

public void drive() {
    if (this.isBatteryEmpty()) {
      throw new IllegalArgumentException("Oh no");
    }

    drive(1);
  }

If the battery is empty, then it throws an exception. Or what am I supposed to add here?

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() {
    if (this.isBatteryEmpty()) {
      throw new IllegalArgumentException("Oh no");
    }

    drive(1);
  }

  public void drive(int laps) {
    lapsDriven += laps;
    barCount -= laps;
  }
}

2 Answers

Hi Massimo,

You're not testing to see if the battery is empty but rather seeing if you've requested that the kart drive more laps than you have bars.

So, if barCount is 2 and you request drive(3), then you've asked too much. This should not drive any laps but throw an exception.

Do this in the drive(int laps) method. Test if there are more or equal barCount to laps, or if laps is less than/equal to barCount. If so, drive the laps & decrement barCount as the method does already. Otherwise, throw the exception.

This would all look like:

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

So, we test laps <= barCount. If this is true, we run the method as-is. Otherwise/else, we throw a new IllegalArgumentException. You probably do this the other way round too, so if laps is greater than barCount, throw the error else run the method. Same difference.

I hope that makes sense.

Steve.

Yes of course now it makes sense.

Thanks for the explanation.

No problem! :+1: :smile: