import java.text.DecimalFormat;

public class Length
{
   // fields(usually private)
   private DecimalFormat F = new DecimalFormat("#.00");
   private double value;
   private String unit;
   private boolean isValid = true;
   
   // constructor (almost always public)
   public Length(double value, String unit)
   {
       this.value = value;
       this.unit = unit;
       if (!((unit.equals("meter")) || (unit.equals("feet"))))
          isValid = false;
   }
   // methods (usually public)
   public void display()
   {
       if (isValid)
            System.out.println(F.format(value) + " " + unit);
       else
            System.out.println("invalid length");
   }
   
   // return a new length which is the old one converted
   // to meter
   public Length convertToMeter()
   {
       if ((isValid) && (unit.equals("feet")))
          return new Length(value / 3.2809, "meter");
       else
          return this;
   }
   
   public Length convertToFeet()
   {
       if ((isValid) && (unit.equals("meter")))
          return new Length(value * 3.2809, "feet");
       else
          return this;
   }
   
   // adds two lengths by first converting them to meters,
   // thus making the answer meters, too.
   Length add(Length l)
   {
      Length l_meter = l.convertToMeter();
      Length meter = this.convertToMeter();
      return new Length(meter.value + l_meter.value, "meter");
   }
}