examples/src/main/java/org/apache/poi/examples/ss/formula/CalculateMortgage.java

/* ====================================================================
   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
==================================================================== */
package org.apache.poi.examples.ss.formula;

import org.apache.poi.ss.formula.OperationEvaluationContext;
import org.apache.poi.ss.formula.eval.ErrorEval;
import org.apache.poi.ss.formula.eval.EvaluationException;
import org.apache.poi.ss.formula.eval.NumberEval;
import org.apache.poi.ss.formula.eval.OperandResolver;
import org.apache.poi.ss.formula.eval.ValueEval;
import org.apache.poi.ss.formula.functions.FreeRefFunction;

/**
 * A simple user-defined function to calculate principal and interest.
 *
 * @author Jon Svede ( jon [at] loquatic [dot] com )
 * @author Brian Bush ( brian [dot] bush [at] nrel [dot] gov )
 *
 */
public class CalculateMortgage implements FreeRefFunction {

    @Override
    public ValueEval evaluate( ValueEval[] args, OperationEvaluationContext ec ) {

        // verify that we have enough data
        if (args.length != 3) {
            return ErrorEval.VALUE_INVALID;
        }

        // declare doubles for values
        double principal, rate, years,  result;
        try {
            // extract values as ValueEval
            ValueEval v1 = OperandResolver.getSingleValue( args[0],
                                                           ec.getRowIndex(),
                                                           ec.getColumnIndex() ) ;
            ValueEval v2 = OperandResolver.getSingleValue( args[1],
                                                           ec.getRowIndex(),
                                                           ec.getColumnIndex() ) ;
            ValueEval v3 = OperandResolver.getSingleValue( args[2],
                                                           ec.getRowIndex(),
                                                           ec.getColumnIndex() ) ;

            // get data as doubles
            principal  = OperandResolver.coerceValueToDouble( v1 ) ;
            rate  = OperandResolver.coerceValueToDouble( v2 ) ;
            years = OperandResolver.coerceValueToDouble( v3 ) ;

            result = calculateMortgagePayment( principal, rate, years ) ;
            System.out.println( "Result = " + result ) ;

            checkValue(result);

        } catch (EvaluationException e) {
            return e.getErrorEval();
        }

        return new NumberEval( result ) ;
    }

    public double calculateMortgagePayment( double p, double r, double y ) {
        double i = r / 12 ;
        double n = y * 12 ;

        return p * (( i * Math.pow((1 + i),n ) ) / ( Math.pow((1 + i),n) - 1));
    }
    /**
     * Excel does not support infinities and NaNs, rather, it gives a #NUM! error in these cases
     *
     * @throws EvaluationException (#NUM!) if <tt>result</tt> is <tt>NaN</> or <tt>Infinity</tt>
     */
     private void checkValue(double result) throws EvaluationException {
         if (Double.isNaN(result) || Double.isInfinite(result)) {
             throw new EvaluationException(ErrorEval.NUM_ERROR);
         }
     }
}