Java Java Objects Harnessing the Power of Objects Throwing Exceptions

Adding logic to a method

How do I add logic to a method so that it throws an IllegalArgumentException?

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) {
    int requestedAmount = lapsDriven + laps;
    if(MAX_BARS < 0) {
      throw new IllegalArgumentException("Too many laps");
    }
    lapsDriven = requestedAmount;
  }
}

2 Answers

Steven Parker
Steven Parker
201,320 Points

The "throw" itself is correct, but:

  • the test should check the argument against the available energy
  • the test (and throw) should be done first in the method
  • the other code that will otherwise be done should not be modified

public void drive(int laps) { int requestedAmount = barCount - laps; if(requestedAmount < 0) { throw new IllegalArgumentException("Battery too low"); } barCount = requestedAmount; } }

Steven Parker
Steven Parker
201,320 Points

The original code body lines need to remain as they were to be done after the test (for those cases where the "throw" is not done).