数学运算工具类

import java.math.BigDecimal;

public class NumberUtil {

	private static final int DEFAULT_DIV_SCALE = 10;

	/**
	 * 相加
	 * @param v1
	 * @param v2
	 * @return double
	 */
	public static double add(double v1, double v2)

	{

		BigDecimal b1 = new BigDecimal(Double.toString(v1));

		BigDecimal b2 = new BigDecimal(Double.toString(v2));

		return b1.add(b2).doubleValue();

	}

	
	public static String add(String v1, String v2)

	{

		BigDecimal b1 = new BigDecimal(v1);

		BigDecimal b2 = new BigDecimal(v2);

		return b1.add(b2).toString();

	}

	/**
	 * 相减
	 * @param v1
	 * @param v2
	 * @return
	 */
	public static double subtract(double v1, double v2)

	{

		BigDecimal b1 = new BigDecimal(Double.toString(v1));

		BigDecimal b2 = new BigDecimal(Double.toString(v2));

		return b1.subtract(b2).doubleValue();

	}

	public static String subtract(String v1, String v2)

	{

		BigDecimal b1 = new BigDecimal(v1);

		BigDecimal b2 = new BigDecimal(v2);

		return b1.subtract(b2).toString();

	}

	/**
	 * 相乘
	 * @param v1
	 * @param v2
	 * @return
	 */
	public static double multiply(double v1, double v2)

	{

		BigDecimal b1 = new BigDecimal(Double.toString(v1));

		BigDecimal b2 = new BigDecimal(Double.toString(v2));

		return b1.multiply(b2).doubleValue();

	}

	public static String multiply(String v1, String v2)

	{

		BigDecimal b1 = new BigDecimal(v1);

		BigDecimal b2 = new BigDecimal(v2);

		return b1.multiply(b2).toString();

	}

	/**
	 * 相除
	 * @param v1
	 * @param v2
	 * @return double
	 */
	public static double divide(double v1, double v2)

	{

		return divide(v1, v2, DEFAULT_DIV_SCALE);

	}

	public static double divide(double v1, double v2, int scale)

	{

		return divide(v1, v2, scale, BigDecimal.ROUND_HALF_EVEN);

	}

	public static double divide(double v1, double v2, int scale, int round_mode) {

		if (scale < 0)

		{

			throw new IllegalArgumentException(
					"The scale must be a positive integer or zero");

		}

		BigDecimal b1 = new BigDecimal(Double.toString(v1));

		BigDecimal b2 = new BigDecimal(Double.toString(v2));

		return b1.divide(b2, scale, round_mode).doubleValue();

	}

	public static String divide(String v1, String v2)

	{

		return divide(v1, v2, DEFAULT_DIV_SCALE);

	}

	public static String divide(String v1, String v2, int scale)

	{

		return divide(v1, v2, DEFAULT_DIV_SCALE, BigDecimal.ROUND_HALF_EVEN);

	}

	public static String divide(String v1, String v2, int scale, int round_mode)

	{

		if (scale < 0)

		{

			throw new IllegalArgumentException(
					"The scale must be a positive integer or zero");

		}

		BigDecimal b1 = new BigDecimal(v1);

		BigDecimal b2 = new BigDecimal(v2);

		return b1.divide(b2, scale, round_mode).toString();

	}

	public static double round(double v, int scale)

	{

		return round(v, scale, BigDecimal.ROUND_HALF_EVEN);

	}

	public static double round(double v, int scale, int round_mode)

	{

		if (scale < 0)

		{

			throw new IllegalArgumentException(
					"The scale must be a positive integer or zero");

		}

		BigDecimal b = new BigDecimal(Double.toString(v));

		return b.setScale(scale, round_mode).doubleValue();

	}

	public static String round(String v, int scale)

	{

		return round(v, scale, BigDecimal.ROUND_HALF_EVEN);

	}

	public static String round(String v, int scale, int round_mode)

	{

		if (scale < 0)

		{

			throw new IllegalArgumentException(
					"The scale must be a positive integer or zero");

		}

		BigDecimal b = new BigDecimal(v);

		return b.setScale(scale, round_mode).toString();
	}

	public static void main(String[] args) {
		System.out.println(2.21 - 2);
		System.out.println(7 * 0.8);

		System.out.println(subtract(312.21, 312));
		System.out.println(multiply(7, 0.8));
	}

}