转载：java.math.BigDecimal的用法

BigDecimal.valueOf(Long.parseLong("12345678"));

BigDecimal op1=new BigDecimal("3.14159");
BigDecimal op2=new BigDecimal("3");       

System.out.println("和="+op1.add(op2));
System.out.println("差="+op1.subtract(op2));
System.out.println("积="+op1.multiply(op1));
System.out.println("商="+op1.divide(op2, BigDecimal.ROUND_UP));
System.out.println("负值="+op1.negate());

System.out.println("指定精度的商="+op1.divide(op2,15, BigDecimal.ROUND_UP));
输出：

和=6.14159
差=0.14159
积=9.8695877281
商=1.04720
负值=-3.14159
指定精度的商=1.047196666666667

对BigDecimal常用方法的归类
package com.org.assistant.util;

import java.math.BigDecimal;

public class Arith {

//默认除法运算精度
private static final int DEF_DIV_SCALE = 10;

//这个类不能实例化
private Arith(){
}

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).doublue();
}

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).doublue();
}

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).doublue();
}

public static double div(double v1,double v2){
return div(v1,v2,DEF_DIV_SCALE);
}

public static double div(double v1,double v2,int scale){
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,BigDecimal.ROUND_HALF_UP).doublue();
}

public static double round(double v,int scale){
if(scale<0){
throw new IllegalArgumentException(
"The scale must be a positive integer or zero");
}
BigDecimal b = new BigDecimal(Double.toString(v));
BigDecimal one = new BigDecimal("1");
return b.divide(one,scale,BigDecimal.ROUND_HALF_UP).doublue();
}

public static float convertsToFloat(double v){
BigDecimal b = new BigDecimal(v);
return b.floatValue();
}

public static int convertsToInt(double v){
BigDecimal b = new BigDecimal(v);
return b.intValue();
}

public static long convertsToLong(double v){
BigDecimal b = new BigDecimal(v);
return b.longValue();
}

public static double returnMax(double v1,double v2){
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.max(b2).doublue();
}

public static double returnMin(double v1,double v2){
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.min(b2).doublue();
}

public static int compareTo(double v1,double v2){
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.compareTo(b2);
}

}