Arith.java

package ch01basic;

import java.math.BigDecimal;

/**
 * Created with IntelliJ IDEA.
 * User: Administrator
 * Date: 12-7-5
 * Time: 下午4:54
 * Java中浮点数的精确计算工具类
 * BigDecimal实例化的时候一定要用String类型
 */
public class Arith {
    // 默认除法运算精度
    private static final int DEF_DIV_SCALE = 2;

    // 这个类不能实例化
    private Arith() {
    }

    /**
     * 精确加法运算
     *
     * @param v1
     * @param v2
     * @return
     */
    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();
    }

    /**
     * 精确减法运算
     *
     * @param v1
     * @param v2
     * @return
     */
    public static double sub(double v1, double v2) {
        BigDecimal b1 = new BigDecimal(Double.toString(v1));
        BigDecimal b2 = new BigDecimal(Double.toString(v2));
        return b1.subtract(b2).doubleValue();
    }

    /**
     * 精确乘法运算
     *
     * @param v1
     * @param v2
     * @return
     */
    public static double mul(double v1, double v2) {
        BigDecimal b1 = new BigDecimal(Double.toString(v1));
        BigDecimal b2 = new BigDecimal(Double.toString(v2));
        return b1.multiply(b2).doubleValue();
    }

    /**
     * 相对精确除法运算
     *
     * @param v1
     * @param v2
     * @param scale
     * @return
     */
    public static double div(double v1, double v2, int scale) {
        if (scale < 0) {
            throw new IllegalArgumentException("scale must not be negetive");
        }
        BigDecimal b1 = new BigDecimal(Double.toString(v1));
        BigDecimal b2 = new BigDecimal(Double.toString(v2));
        return b1.divide(b2, scale, BigDecimal.ROUND_HALF_UP).doubleValue();
    }

    /**
     * 相对精确除法运算，保留小数点2位
     *
     * @param v1
     * @param v2
     * @return
     */
    public static double div(double v1, double v2) {
        return div(v1, v2, DEF_DIV_SCALE);
    }

    /**
     * 精确四舍五入运算
     *
     * @param v
     * @param scale
     * @return
     */
    public static double round(double v, int scale) {
        if (scale < 0) {
            throw new IllegalArgumentException("scale must not be negetive");
        }
        BigDecimal b = new BigDecimal(Double.toString(v));
        BigDecimal one = new BigDecimal("1");
        return b.divide(one, scale, BigDecimal.ROUND_HALF_UP).doubleValue();
    }
}