Present Value class error

package business;

import java.text.NumberFormat;

/**
 *
 * @author
 */
public class PV extends Financial {
    public static final String FUTAMTDESC = "Future Amount";
    public static final String RESULTDESC = "Present Value";

    private boolean built;
    private double[] bbal, iearn, ebal;

       public PV(){
        super();
        this.built = false;
    }

    public PV (double a, double r, int t) {
        super(a,r,t);
        this.built = false;
        if (super.isValid()) {
            buildPV();
        }
    }

    private void biuldPV () {
          try {
            this.bbal = new double[super.getTerm()];
            this.iearn = new double[super.getTerm()];
            this.ebal = new double[super.getTerm()];
            double morate = 0;
            double denom = 0;

            this.bbal[0] = 0;
            for (int i=0; i < super.getTerm(); i++) {
               if (i > 0) {
                   this.bbal[i] = this.ebal[i-1];
               }
               morate = super.getRate() / 12.0;
               denom = super.getAmt() /Math.pow((1+morate), super.getTerm());
               this.iearn[i] = (this.bbal[i] + super.getAmt()) * (super.getRate() / 12.0);
               this.ebal[i] = this.bbal[i] + super.getAmt() + this.iearn[i];
            }
            this.built = true;
        } catch (Exception e) {
            super.setErrorMsg("PV build error.");
            this.built = false;
        }
    }

       @Override
    public double getBegBal(int mo) {
        if (!this.built) {
            buildPV();
            if (!this.built) {
                return -1;
            }
        }
        if (mo < 1 || mo > super.getTerm()) {
            return -1;
        }
        return this.bbal[mo-1];
    }

    @Override
    public double getInterest(int mo) {
        if (!this.built) {
            buildPV();
            if (!this.built) {
                return -1;
            }
        }
        if (mo < 1 || mo > super.getTerm()) {
            return -1;
        }
        return this.iearn[mo-1];
    }

    @Override
    public double getPrincipal (int mo) {
        if (!this.built) {
            buildPV();
            if (!this.built) {
                return -1;
            }
        }
        return super.getAmt();
    }

    @Override
    public double getEndBal(int mo){
        if (!this.built) {
            buildPV();
            if (!this.built) {
                return -1;
            }
        }
        if (mo < 1 || mo > super.getTerm()) {
            return -1;
        }
        return this.ebal[mo-1];
    }

    @Override
    public double getResult() {
        if (!this.built) {
            buildPV();
            if (!this.built) {
                return -1;
            }
        }
        return this.ebal[super.getTerm()-1];
    }

    @Override
    public String getTitle () {
        NumberFormat curr = NumberFormat.getCurrencyInstance();
        NumberFormat pct = NumberFormat.getPercentInstance();
        pct.setMaximumFractionDigits(3);

        return "Annuity Schedule " + curr.format(super.getAmt()) + " per month @ " + pct.format(super.getRate()) + " for " + super.getTerm() + " months.";
    }
}