Code Challenge on Helper Methods

I am completely stuck on this question. It is:

Okay, so let's use our new isFullyCharged helper method to change our implementation details of the charge method. Let's make it so it will only charge until the battery reports being fully charged. Let's use the ! symbol and a while loop. Inside the loop increment mBarsCount

See my code attached. Do I need to name an object in order to use its method like this:

while(!gokart.isFullyCharged()){ mBarsCount++; }

or is it something else? I've been stuck for half an hour and unfornately I need to go to bed :( hope someone can answer by morning. Thank you :-)

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

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

  public String getColor() {
    return mColor;
  }

  public void charge() {
    mBarsCount = MAX_ENERGY_BARS;
  }

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

  public boolean isFullyCharged() {
    return mBarsCount == MAX_ENERGY_BARS;
  }
  while (!isFullyCharged()){
    mBarsCount++;
  }

}