CurrencyManstissa.java

package scrap.stackoverflow;

import java.math.BigDecimal;
import java.text.DecimalFormat;

public class CurrencyManstissa {
	
	private static final DecimalFormat MONEY_FORMAT = new DecimalFormat("#,##0.00");
	private static final String STRING_FORMAT = "%s %5d %30s";
	private static final BigDecimal D100 = BigDecimal.valueOf(100);

	/**
	 * Calculate the GDP table in jumps of 10 years for the given start value and growth rate.
	 * @param start starting GDP in dollars
	 * @param growthPct the growth rate (e.g., 3 = 3% growth)
	 * @param totalYears the number of years the table will cover 
	 */
	public static void makeGDPTable(double start, int growthPct, int totalYears) {
		double startDouble = start * 100;
		double growthDouble = (100 + growthPct) / 100.0;
		
		BigDecimal startDecimal = BigDecimal.valueOf(start);
		BigDecimal growthDecimal = BigDecimal.valueOf(100 + growthPct).divide(D100);
		
		for (int year = 0; year < totalYears; year += 10) {
			double gdpDouble = startDouble * Math.pow(growthDouble, year);
			BigDecimal gdpDecimal = startDecimal.multiply(growthDecimal.pow(year));
			double delta = gdpDouble / 100 - gdpDecimal.doubleValue();
			System.out.println(String.format(STRING_FORMAT, "double ", year, "$ " + MONEY_FORMAT.format(gdpDouble / 100)));
			System.out.print(String.format(STRING_FORMAT, "Decimal", year, "$ " + MONEY_FORMAT.format(gdpDecimal.doubleValue())));
			System.out.println(String.format("  (%.10f)", delta));
		}
	}
	
	public static void main(String[] args) {
		makeGDPTable(1_000_000_000, 5, 200);
	}

}