Java Java Objects Harnessing the Power of Objects Handling Exceptions

This does not work? Why? Please help!

Task: Example.java contains a program using the GoKart class we have been building (included for you to reference).

Protect the call to kart.drive by handling the IllegalArgumentException that is thrown when not enough battery remains. Print out the message from the exception to the screen as you catch the exception.

Please help me with this. I await anyone's response.

Example.java
class Example {

  public static void main(String[] args) {
    GoKart kart = new GoKart("purple");
    if (kart.isBatteryEmpty()) {
      System.out.println("The battery is empty");
    }
    kart.drive(42);
    while (kart.!isEmpty()) {
      System.out.println("Vroom!");
    }
    if (kart.isBatteryEmpty()) {
      System.out.println("No more batteries!");
    }
  }
}
GoKart.java
class GoKart {
  public static final int MAX_BARS = 8;
  private int barCount;
  private String color;
  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) {
    if (laps > barCount) {
      throw new IllegalArgumentException("Not enough battery remains");
    }
    lapsDriven += laps;
    barCount -= laps;
  }

}

3 Answers

Daniel Turato
PRO
Daniel Turato
Java Web Development Techdegree Graduate 30,105 Points

To catch an error, you need to surround the risky code inside a try catch block. Then in the catch part, you expect and exception and handle it in some sort of way which in this case is outputting the error message.

class Example {

  public static void main(String[] args) {
    GoKart kart = new GoKart("purple");
    if (kart.isBatteryEmpty()) {
      System.out.println("The battery is empty");
    }
    try {
       kart.drive(42);
    } catch (IllegalArgumentException ex) {
      System.out.println(ex.getMessage());
    }

  }

}

Hopefully this helps

However, I have a question: Where did you get the ex?

Daniel Turato
Daniel Turato
Java Web Development Techdegree Graduate 30,105 Points

ex is just a local variable name for the exception so you can access methods on the exception. You can name it whatever you want. So it's basically doing this:

IllegalArgumentException ex = new IllegalArgumentException();

Of course! I totally forgot about the try catch block! Thank you so much for helping me!

Ok, thanks!