处理大数据

package com.jdk7.chapter3;

import java.math.BigDecimal;

public class HandleBigDecimal {
    public static double add(double a1, double a2){
        //声明BigDecimal对象进行数学计算时，参数使用String会比较准确
        BigDecimal a = new BigDecimal(Double.valueOf(a1).toString());
        BigDecimal b = new BigDecimal(Double.valueOf(a2).toString());
        System.out.println(a+"+"+b+" = "+a.add(b));
        return a.add(b).doubleValue();
    }
    
    public static double sub(double s1,double s2){
        BigDecimal a = new BigDecimal(Double.valueOf(s1).toString());
        BigDecimal b = new BigDecimal(Double.valueOf(s2).toString());
        System.out.println(a+"-"+b+" = "+a.subtract(b));
        return a.subtract(b).doubleValue();
    }
    
    public static double multiply(double m1, double m2){
        BigDecimal a = new BigDecimal(Double.valueOf(m1).toString());
        BigDecimal b = new BigDecimal(Double.valueOf(m2).toString());
        System.out.println(a+"*"+b+" = "+a.multiply(b));
        return a.multiply(b).doubleValue();
    }
    
    public static double div(double d1, double d2){
        return div(d1, d2, 4);
    }
    
    public static double div(double v1, double v2, int scale){
        if(scale<0){
            System.err.println("精度不能小于0");
            return 0;
        }else{
            BigDecimal a = new BigDecimal(Double.valueOf(v1).toString());
            BigDecimal b = new BigDecimal(Double.valueOf(v2).toString());
            System.out.println(a+"/"+b+" = "+a.divide(b, scale));
            return a.divide(b, scale).doubleValue();
        }
    }
    
    /**
     * 计算整数阶乘，当整数超过17时，阶乘超出long的范围,此时阶乘结果要用BigDecimal类型保存
     * @return
     */
    public static BigDecimal getFactorial(int n){
        if(n<0){
            System.out.println((new BigDecimal("-1")).toString());
            return new BigDecimal("-1");
        }else if(n==0){
            System.out.println((new BigDecimal("0")).toString());
            return new BigDecimal("0");
        }else{
            BigDecimal result = new BigDecimal("1");
            for(;n>0;n--){
                result = result.multiply(new BigDecimal(Integer.valueOf(n).toString()));
            }
            System.out.println(result.toString());
            return result;
        }
    }
    public static void main(String[] args) {
        add(0.01,0.05);
        sub(1.0,0.42);
        multiply(4.015,100);
        div(123.3,100);
        div(123.3,100,4);
//        div(123.3,100,-1);
        getFactorial(-1);
        getFactorial(0);
        getFactorial(30);
        
        BigDecimal a = new BigDecimal(0.1);        //double类型的构造函数
        BigDecimal b = new BigDecimal("0.1");    //String类型的构造函数
        BigDecimal c = new BigDecimal("0.10");    //String类型的构造函数
        System.out.println("a = "+a.toString());
        System.out.println("b = "+b.toString());
        System.out.println("c = "+c.toString());
        System.out.println("a.equals(b) = "+a.equals(b));        //进行字符串的比较
        System.out.println("a.compareTo(b) = "+a.compareTo(b));    //进行数值的比较,a是double构造对象，大于b
        System.out.println("b.compareTo(c) = "+b.compareTo(c));
        
    }
}

处理结果：
0.01+0.05 = 0.06
1.0-0.42 = 0.58
4.015*100.0 = 401.5000
123.3/100.0 = 1.2
123.3/100.0 = 1.2
-1
0
265252859812191058636308480000000
a = 0.1000000000000000055511151231257827021181583404541015625
b = 0.1
c = 0.10
a.equals(b) = false
a.compareTo(b) = 1
b.compareTo(c) = 0