BigDecimal加减乘除，比较

BigDecimal通过compareTo方法来进行比较.
返回的结果是int类型,-1表示小于,0是等于,1是大于.

java.math.BigDecimal。

BigDecimal一共有4个够造方法:
public static double add(double v1,double v2) --- 加
public static double sub(double v1,double v2) --- 减
public static double mul(double v1,double v2) --- 乘
public static double div(double v1,double v2) --- 除

//加法--参数为：String，String   四舍五入保留num位小数
public BigDecimal add(String num1, String num2, int num) {
    BigDecimal result = new BigDecimal(num1).add(new BigDecimal(num2)).setScale(num, BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}
//加法--参数为：Double，Double 四舍五入保留num位小数
public static BigDecimal add(Double num1, Double num2, int num) {
    BigDecimal result = BigDecimal.valueOf(num1).add(BigDecimal.valueOf(num2)).setScale(num, BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}
//减法--参数为：String，String 四舍五入保留num位小数
public static BigDecimal subtract(String num1, String num2, int num) {
    BigDecimal result = new BigDecimal(num1).subtract(new BigDecimal(num2)).setScale(num, BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}
//减法--参数为：Double，Double 四舍五入保留num位小数
public static BigDecimal subtract(Double num1, Double num2, int num) {
    BigDecimal result = BigDecimal.valueOf(num1).subtract(BigDecimal.valueOf(num2)).setScale(num, BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}
//乘法--参数为：String，String 四舍五入保留num位小数
public static BigDecimal multiply(String num1, String num2, int num) {
    BigDecimal result = new BigDecimal(num1).multiply(new BigDecimal(num2)).setScale(num, BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}
//乘法--参数为：Double，Double 四舍五入保留num位小数
public static BigDecimal multiply(Double num1, Double num2, int num) {
    BigDecimal result = BigDecimal.valueOf(num1).multiply(BigDecimal.valueOf(num2)).setScale(num, BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}
//除法--参数为：String，String 四舍五入保留num位小数
public static BigDecimal divide(String num1, String num2, int num) {
    BigDecimal result = new BigDecimal(num1).divide(new BigDecimal(num2),num,BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}
//除法--参数为：Double，Double 四舍五入保留num位小数
public BigDecimal divide(Double num1, Double num2, int num) {
    BigDecimal result = BigDecimal.valueOf(num1).divide(BigDecimal.valueOf(num2),num,BigDecimal.ROUND_HALF_UP);
    result = result.compareTo(new BigDecimal("0E-8")) == 0 ? new BigDecimal("0") : result;
    return result;
}