MoneyUtil.java

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.text.NumberFormat;
import java.util.Arrays;
import java.util.Locale;
import java.util.function.BinaryOperator;

/**
 * A simple utility class to calculate Money related calculation. It provides
 * three private properties along with setters and these following default
 * values
 * <ul>
 * <li><code>toPrecision: 2</code></li>
 * <li><code>locale: java.utils.Locale.US</code></li>
 * <li><code>roundingMode: java.math.RoundingMode.HALF_EVEN</code></li>
 * </ul>
 *
 * @author Nur Rony
 * @since v1.0.0
 */
final public class MoneyUtil {
  private static int toPrecision = 2;
  private static Locale locale = Locale.US;
  private static RoundingMode roundingMode = RoundingMode.HALF_EVEN;
  public static final BigDecimal ONE_HUNDRED = new BigDecimal(100);

  private MoneyUtil() {
    throw new IllegalStateException("MoneyUtil Utility Class");
  }

  /**
   * Converts array of {@link String} to array of {@link BigDecimal}
   *
   * @param numbers array of {@link String}
   * @return {@link BigDecimal[]}
   * @throws NumberFormatException
   */
  private static BigDecimal[] toBigDecimalArray(String... numbers) throws NumberFormatException {
    return Arrays.stream(numbers).sequential().map(BigDecimal::new).toArray(BigDecimal[]::new);
  }

  /**
   * Set precision for calculation
   *
   * @param toPrecision precision to set for decimal part
   */
  public static void setPrecision(int toPrecision) {
    MoneyUtil.toPrecision = toPrecision;
  }

  /**
   * Set rounding for calculation; defaults: {@link RoundingMode.HALF_EVEN}
   *
   * @param roundingMode precision to set for decimal part
   */
  public static void setRoundingMode(RoundingMode roundingMode) {
    MoneyUtil.roundingMode = roundingMode;
  }

  /**
   * Format a {@link BigDecimal} number for given locale
   *
   * @param number number to format
   * @param locale locale of the formatted number
   * @return {@link String}
   */
  public static String formatToLocale(BigDecimal number, Locale locale) {
    return NumberFormat.getNumberInstance(locale == null ? MoneyUtil.locale : locale).format(number);
  }

  /**
   * Format a {@link BigDecimal} number for given locale with currency symbol
   *
   * @param number number to format
   * @param locale locale of the formatted number
   * @return {@link String}
   */
  public static String formatToCurrency(BigDecimal number, Locale locale) {
    return NumberFormat.getCurrencyInstance(locale == null ? MoneyUtil.locale : locale).format(number);
  }

  /**
   * Add numbers given as {@link String}
   *
   * @param numbers array of {@link String}
   * @return {@link BigDecimal}
   *
   * @see {@link #add(BigDecimal...)}
   * @see {@link #toBigDecimalArray(String...)}
   */
  public static BigDecimal add(String... numbers) throws NumberFormatException {
    return add(toBigDecimalArray(numbers));
  }

  /**
   * Add numbers given as {@link BigDecimal}
   *
   * @param numbers array of {@link BigDecimal}
   * @return {@link BigDecimal}
   */
  public static BigDecimal add(BigDecimal... numbers) {
    return Arrays.stream(numbers).sequential().reduce(BigDecimal.ZERO, BigDecimal::add)
        .setScale(toPrecision, roundingMode);
  }

  /**
   * Subtracts numbers given as {@link String}
   *
   * @param numbers array of {@link String}
   * @return {@link BigDecimal}
   * @see {@link #subtract(BigDecimal...)}
   */
  public static BigDecimal subtract(String... numbers) throws NumberFormatException {
    return subtract(toBigDecimalArray(numbers));
  }

  /**
   * Subtracts numbers given as {@link BigDecimal}
   *
   * @param numbers arrays of {@link BigDecimal}
   * @return {@link BigDecimal}
   */
  public static BigDecimal subtract(BigDecimal... numbers) {
    BigDecimal[] shiftedArray = Arrays.copyOfRange(numbers, 1, numbers.length);
    return Arrays.stream(shiftedArray).sequential().reduce(numbers[0], BigDecimal::subtract)
        .setScale(toPrecision, roundingMode);
  }

  /**
   * Multiplies numbers given as {@link String}
   *
   * @param numbers arrays of {@link String}
   * @return {@link BigDecimal}
   * @see {@link #multiply(BigDecimal...)}
   * @see {@link #toBigDecimalArray(String...)}
   */
  public static BigDecimal multiply(String... numbers) throws NumberFormatException {
    return multiply(toBigDecimalArray(numbers));
  }

  /**
   * Multiplies numbers given as {@link BigDecimal}
   *
   * @param numbers arrays of {@link BigDecimal}
   * @return {@link BigDecimal}
   */
  public static BigDecimal multiply(BigDecimal... numbers) {
    return Arrays.stream(numbers).sequential().reduce(BigDecimal.ONE, BigDecimal::multiply)
        .setScale(toPrecision, roundingMode);
  }

  /**
   * Divides numbers given as {@link String}
   *
   * @param numbers arrays of {@link String}
   * @return {@link BigDecimal}
   *
   * @see {@link #divide(BigDecimal...)}
   * @see {@link #toBigDecimalArray(String...)}
   */
  public static BigDecimal divide(String... numbers) throws NumberFormatException {
    return divide(toBigDecimalArray(numbers));
  }

  /**
   * Divides numbers given as {@link BigDecimal}
   *
   * @param numbers arrays of {@link BigDecimal}
   * @return {@link BigDecimal}
   */
  public static BigDecimal divide(BigDecimal... numbers) {
    BigDecimal[] shiftedArray = Arrays.copyOfRange(numbers, 1, numbers.length);
    BinaryOperator<BigDecimal> accumulator = (result, number) -> result.divide(number, 2, roundingMode);
    return Arrays.stream(shiftedArray).sequential().reduce(numbers[0], accumulator).setScale(toPrecision, roundingMode);
  }

  /**
   * Calculates percentage for given base number
   *
   * @param base       number to calculate percentage on
   * @param percentage amount of percentage
   * @return {@link BigDecimal}
   *
   * @see {@link #percentage(BigDecimal, BigDecimal)}
   */
  public static BigDecimal percentage(String base, String percentage) {
    return percentage(new BigDecimal(base), new BigDecimal(percentage));
  }

  /**
   * Calculates percentage for given base number
   *
   * @param base       number to calculate percentage on
   * @param percentage amount of percentage
   * @return {@link BigDecimal}
   */
  public static BigDecimal percentage(BigDecimal base, BigDecimal percentage) {
    return (base.multiply(percentage).divide(ONE_HUNDRED)).setScale(toPrecision, roundingMode);
  }
}