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Java Java Objects Harnessing the Power of Objects Throwing Exceptions

Jackie Wang
Jackie Wang
479 Points
Posted by Jackie Wang
Jackie Wang
479 Points

You probably already spotted the error in the drive method that accepts laps. You can drive way more laps than our batte

You probably already spotted the error in the drive method that accepts laps. You can drive way more laps than our battery can handle. Let's fix it.

Add logic to the drive method so that it throws an IllegalArgumentException if there aren't enough bars to support the laps request. Remember it takes 1 bar of energy to go around a lap.

I think it's good what's wrong with my program

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 newAmount = lapsDriven + barCount;
      if(newAmount < 0) {
        throw new IllegalArgumentException();
      }
  }

}

3 Answers

Steve Hunter
Steve Hunter
57,712 Points

Hi Jackie,

There's a couple of ways of doing this depending on how you do your conditional test. However, what we're trying to achieve is a check as to whether the parameter passed in, laps, is larger than the number of bars in the kart's possession, barCount. So, if laps is bigger tha barCount, don't do any laps but do throw the exception. Alternatively, you can test if laps is less than or equal to barCount, if so, do the laps, else throw the exception.

The first option is probably more elegant as it involves less code; I'll let you figure that one out, the second way would look something like this:

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

I hope that makes sense, if not, let me know and I'll try again!

Steve.

Steve Hunter
Steve Hunter
57,712 Points

No problem! :+1:

james south
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points
james south
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points

you don't need to make a new variable. you just need to compare laps with your remaining energy and if there's not enough energy, throw the error.

Jackie Wang
Jackie Wang
479 Points
Jackie Wang
Jackie Wang
479 Points

So which variable should I compare with

Jackie Wang
Jackie Wang
479 Points
Jackie Wang
Jackie Wang
479 Points 
if(barCount < 0) {
        throw new IllegalArgumentException();
      }

if i do this it will say that Make sure you throw a new IllegalArgumentException if the requested amount of laps would make the battery less than zero.

Lawrence Babay
Lawrence Babay
6,941 Points
Lawrence Babay
Lawrence Babay
6,941 Points

You definitely don't need a new variable here. All you have to do is compare the laps > barCount then throw the IllegalArgumentException.