public class CircleAreaCalc {

    private BigDecimal pi;

    public CircleAreaCalc(int numDigits) {
        PiCalc piCalc = new PiCalc(numDigits);
        pi = piCalc.compute();
    }

    public BigDecimal area(BigDecimal radius) {
        BigDecimal area = radius.pow(2);
        area = area.multiply(pi);
        return area;
    }
}