GreatNumber.java實現了兩個超大數值(整數或浮點數都可以)的相加，也可以進行精度控制。
package org.siyn.util;
/** *//**
* “超大數”實用類
* @author siyn
* @date 2008-04-27
*
*/
public class GreatNumber
{
private GreatNumber(){}
/** *//**
* 超大數字相加
*
* @param {String}greatNumber1 待加“超大數1”
* @param {String}greatNumber2 待加“超大數2”
* @param {int}precision 精度(如果為負數，不限精度)
*
* @return String 兩個“超大數”之和
* @throws NumberFormatException
*/
public static String add(String greatNumber1,String greatNumber2,int precision) throws RuntimeException
{
StringBuffer result = new StringBuffer("");
//小數部分Fractional part
String greatNumber1_FraPart = "";
String greatNumber2_FraPart = "";
//整數部分Integral part
String greatNumber1_IntPart = "";
String greatNumber2_IntPart = "";
//小數點位置
int locationOfDot = 0;
//整數的小數部分補充0
String zero = "";
for(int i=0;i<precision ;i++)
{
zero +="0";
}
//劃分整數部分和小數部分
if(greatNumber1.indexOf('.')==-1)
{
greatNumber1_FraPart = zero;
greatNumber1_IntPart = greatNumber1;
}
else
{
locationOfDot = greatNumber1.indexOf('.');
greatNumber1_FraPart = greatNumber1.substring(locationOfDot+1);
greatNumber1_IntPart = greatNumber1.substring(0,locationOfDot);
}
//System.out.println("greatNumber1="+greatNumber1_IntPart+"."+greatNumber1_FraPart);
if(greatNumber2.indexOf('.')==-1)
{
greatNumber2_FraPart = zero;
greatNumber2_IntPart = greatNumber2;
}
else
{
locationOfDot = greatNumber2.indexOf('.');
greatNumber2_FraPart = greatNumber2.substring(locationOfDot+1);
greatNumber2_IntPart = greatNumber2.substring(0,locationOfDot);
}
//System.out.println("greatNumber2="+greatNumber2_IntPart+"."+greatNumber2_FraPart);
//小數部分
StringBuffer result_FraPart = new StringBuffer();
int carry = 0;
int g1_FraPart_len = greatNumber1_FraPart.length();
int g2_FraPart_len = greatNumber2_FraPart.length();
int len = g1_FraPart_len>g2_FraPart_len?g1_FraPart_len:g2_FraPart_len;
//精度控制
if(precision<0)precision = len;
len = len<precision?precision:len;//取大
//String up_FraPart = g1_FraPart_len>g2_FraPart_len?greatNumber1_FraPart:greatNumber2_FraPart;
//if(precision<up_FraPart.length()) carry = up_FraPart.charAt(precision)-48>4?1:0;
for(int i=len-1;i>=0;i--)
{
char c1 = g1_FraPart_len > i?greatNumber1_FraPart.charAt(i):'0';
char c2 = g2_FraPart_len > i?greatNumber2_FraPart.charAt(i):'0';
if(Character.isDigit(c1) && Character.isDigit(c2))
{
int c = ( (c1-48)+(c2-48)+carry )%10;
//進位
if(i==precision)
{
carry = ( (c1-48)+(c2-48)+carry )/5;
carry = carry>0?1:0;
}
else
{
carry = ( (c1-48)+(c2-48)+carry )/10;
}
//精度控制
if(i<precision) result_FraPart.insert(0, c);
}
else
{
throw new NumberFormatException("輸入參數存在非數字字符.");
}
}
//整數部分
StringBuffer result_IntPart = new StringBuffer("");
int g1_IntPart_len = greatNumber1_IntPart.length();
int g2_IntPart_len = greatNumber2_IntPart.length();
len = g1_IntPart_len>g2_IntPart_len?g1_IntPart_len:g2_IntPart_len;
for(int i=0;i<len;i++)
{
char c1 = g1_IntPart_len > i?greatNumber1_IntPart.charAt(g1_IntPart_len-1-i):'0';
char c2 = g2_IntPart_len > i?greatNumber2_IntPart.charAt(g2_IntPart_len-1-i):'0';
if(Character.isDigit(c1) && Character.isDigit(c2))
{
int c = ( (c1-48)+(c2-48)+carry )%10;
carry = ( (c1-48)+(c2-48)+carry )/10;
result_IntPart.insert(0, c);
}
else
{
throw new NumberFormatException("輸入參數存在非數字字符.");
}
}
if(carry!=0) result_IntPart.insert(0, carry);//最后一個進位
result.append(result_IntPart);
result.append(".");
result.append(result_FraPart);
return result.toString();
}
/** *//**
* 超大數字相加(不限精度)
*
* @param {String}greatNumber1 待加超大數1
* @param {String}greatNumber2 待加超大數1
*
* @return String 兩個超大數之和
* @throws NumberFormatException
*/
public static String add(String greatNumber1,String greatNumber2) throws RuntimeException
{
return GreatNumber.add(greatNumber1, greatNumber2, -1);
}
public static void main(String[] aa)
{
String greatNumber1 = "9999999999999999999999999999999999999983.123456789";
String greatNumber2 = "17.2";
String result = GreatNumber.add(greatNumber1, greatNumber2,-6);
System.out.println(" " + greatNumber1);
System.out.println(" + " + greatNumber2);
System.out.println("----------------------------------------------------------");
System.out.println(" = " + result);
}
}
弄好了才發現sun提供類BigDecimal＆BigInteger實現這個功能，哎~~~~
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