poi/src/java/org/apache/poi/hssf/record/formula/functions/Countblank.java

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   this work for additional information regarding copyright ownership.
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package org.apache.poi.hssf.record.formula.functions;

import org.apache.poi.hssf.record.formula.eval.AreaEval;
import org.apache.poi.hssf.record.formula.eval.BlankEval;
import org.apache.poi.hssf.record.formula.eval.ErrorEval;
import org.apache.poi.hssf.record.formula.eval.NumberEval;
import org.apache.poi.hssf.record.formula.eval.RefEval;
import org.apache.poi.hssf.record.formula.eval.ValueEval;
import org.apache.poi.hssf.record.formula.functions.CountUtils.I_MatchPredicate;

/**
 * Implementation for the function COUNTBLANK
 * <p>
 *  Syntax: COUNTBLANK ( range )
 *    <table border="0" cellpadding="1" cellspacing="0" summary="Parameter descriptions">
 *      <tr><th>range&nbsp;&nbsp;&nbsp;</th><td>is the range of cells to count blanks</td></tr>
 *    </table>
 * </p>
 *
 * @author Mads Mohr Christensen
 */
public final class Countblank implements Function {

	public ValueEval evaluate(ValueEval[] args, int srcRowIndex, short srcColumnIndex) {
		if (args.length != 1) {
			// TODO - it doesn't seem to be possible to enter COUNTBLANK() into Excel with the wrong arg count
			// perhaps this should be an exception
			return ErrorEval.VALUE_INVALID;
		}

		double result;
		ValueEval arg0 = args[0];
		if (arg0 instanceof RefEval) {
			result = CountUtils.countMatchingCell((RefEval) arg0, predicate);
		} else if (arg0 instanceof AreaEval) {
			result = CountUtils.countMatchingCellsInArea((AreaEval) arg0, predicate);
		} else {
			throw new IllegalArgumentException("Bad range arg type (" + arg0.getClass().getName() + ")");
		}
		return new NumberEval(result);
	}

	private static final I_MatchPredicate predicate = new I_MatchPredicate() {

		public boolean matches(ValueEval valueEval) {
			// Note - only BlankEval counts
			return valueEval == BlankEval.INSTANCE;
		}
	};
}