make sure you throw the exception before changing mBarsCount field

Question

public void drive(int laps) { // Other driving code omitted for clarity purposes

mBarsCount -= laps;
if(mBarsCount<=-1){
throw new IllegalArgumentException("Not enough battery remains");
}
}

GoKart.java

public class GoKart {
  public static final int MAX_BARS = 8;
  private String mColor;
  private int mBarsCount;

  public GoKart(String color) {
    mColor = color;
    mBarsCount = 0;
  }

  public String getColor() {
    return mColor;
  }

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

  public void drive(int laps) {
    // Other driving code omitted for clarity purposes

    mBarsCount -= laps;
    if(mBarsCount<=-1){
    throw new IllegalArgumentException("Not enough battery remains");
    }
    }

  public void charge() {
    while (!isFullyCharged()) {
      mBarsCount++;
    }
  }

  public boolean isBatteryEmpty() {
    return mBarsCount == 0;
  }

  public boolean isFullyCharged() {
    return mBarsCount == MAX_BARS;
  }

}

Answer 1 · 2015-10-17T15:35:51Z

October 17, 2015 3:35pm

Hey Neelesh,

Two things:

Our if statement should just check if our mBarsCount has a value greater than the "laps" value (the value we pass in as a constructor). if our mBarsCount is less than the value we pass in, then we can't subtract from it because it would bring a negative which we dont want. When that happens, we want to throw the exception. Also the subtraction should happen after we check the if statement. So in visual format:

Answer.java

  public void drive(int laps) {
    // Other driving code omitted for clarity purposes


    if(mBarsCount< laps){ //check if mBarsCount is less than "laps"
    throw new IllegalArgumentException("Not enough battery remains"); //if true then error
    }
        mBarsCount -= laps; //otherwise peacefully subtract desired value
    }

I have also found out that the method below works as well however the above solution is more logical because what we had a value of 1 in our mBarsCount but we passed in a parameter of 5. It would pass the if statement but then bring back a error because we can't subtract 5 from 1.

I added a few comments below

Alternative.java

  public void drive(int laps) {
    // Other driving code omitted for clarity purposes
    if (mBarsCount==0) { //check if we have any value in our mBarsCount
     throw new IllegalArgumentException ("Not enough battery remains"); //if no value inside, then throw exception
    }
    mBarsCount -= laps; 
//if we do have a value, then subtract the value that we passed in. but as i stated above, this method will bring back errors if our "lap" value is greater than our "mBarsCount" value
  }

I hope that helped,

Kevin

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Neelesh Tewani

Neelesh Tewani

make sure you throw the exception before changing mBarsCount field

1 Answer

Kevin Faust

Kevin Faust