It's not working out

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() {

// the while loop is needed inside the charge() method
// The isFullyCharged method is nice, no need to change it. 
// Inside the charge method, you can use isFullyCharged method to write a condition for a while loop

        while(!isFullyCharged()){ 
// dont forget the ! to say while "NOT" fully charged
// increment mBarsCount
          mBarsCount++;
  }
}

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

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