JAVA写的中文金额转换程序

闲来无事，突然想自己写个中文金额转换程序，想做到简洁高效优雅，看似简单的需求，做起来不一定就容易，特别是对于中间多个零的情况，还有单位换算。

package com.zsmud.ui;

import java.math.BigInteger;
import java.text.DecimalFormat;

/**
 * 最大到九千兆之上
 * @author Zhengsm
 * @date 2012/12/10
 */
public class ToChineseAmount {
	
	private static char[] chineseAmt = {'零','壹','贰','叁','肆','伍','陆','柒','捌','玖'};
	private static char[] units = {'拾','佰','仟'};//i=1,i=2,i=3,i=5,i=6,i=7,i=9,i=10,i=11
	private static char[] chineseUnits = {'元','万','亿','兆'};//i=0,i=4,i=8，
	private static char[] smallUnits = {'分','角'};
	
	public static String formatInt(BigInteger num) {
		if(num.equals(BigInteger.ZERO)) return "零元";
		if(num.toString().length()>16) throw new RuntimeException("too max num");
		StringBuffer result = new StringBuffer("");
		BigInteger radix = new BigInteger("10");
		int i=0;
		char preChar = 0;
		while(num.compareTo(BigInteger.ZERO)==1){			
			StringBuffer tmp = new StringBuffer();
			BigInteger rest = num.mod(radix);
			num = num.divide(radix);
			if(rest.equals(BigInteger.ZERO) && preChar!='零' && inArray(chineseAmt,preChar)){
				tmp.append('零');
			}else if(!rest.equals(BigInteger.ZERO)){
				tmp.append(chineseAmt[rest.intValue()]);
				if(i%4!=0) tmp.append(units[i%4-1]);
			}
			if(i%4==0) {
				if(tmp.length()>0 && tmp.charAt(0)=='零') 
					tmp.insert(0, chineseUnits[i/4]);
				else
					tmp.append(chineseUnits[i/4]);
			}
			preChar = tmp.length()>0? tmp.charAt(0):0;
			i++;
			result.insert(0, tmp);
		}
		
		return result.toString();
	}
	
	public static String formatSmall(int small){
		if(small>100) throw new RuntimeException("too small");
		StringBuffer result = new StringBuffer("");
		char preChar = 0;
		int i=0;
		while(small>0){
			StringBuffer tmp = new StringBuffer();
			int rest = small%10;
			small = small/10;
			if(rest==0 && preChar!='零' && inArray(chineseAmt,preChar)){
				tmp.append('零');
			}else if(rest!=0){
				tmp.append(chineseAmt[rest]);
				tmp.append(smallUnits[i]);
			}
			preChar = tmp.length()>0? tmp.charAt(0):0;
			i++;
			result.insert(0, tmp);
		}
		return result.toString();
	}
	
	private static boolean inArray(char[] array,char c){
		for(char ch : array){
			if(ch == c) return true;
		}
		return false;
	}
	
	public static String format(double num){
		DecimalFormat df = new DecimalFormat("#.00");
		String input = df.format(num);
		StringBuffer sb = new StringBuffer();
		if(input.indexOf('.')!=-1) {
			sb.append(formatInt(new BigInteger(input.substring(0, input.indexOf('.')))));
			sb.append(formatSmall(Integer.parseInt(input.substring(input.indexOf('.')+1))));
		}
		return sb.toString();
	}
	
	public static void main(String[] args){
		System.out.println(formatInt(new BigInteger("909")));
		System.out.println(formatInt(new BigInteger("9009")));
		System.out.println(formatInt(new BigInteger("9099")));
		System.out.println(formatInt(new BigInteger("909099")));
		System.out.println(formatInt(new BigInteger("909909")));
		System.out.println(formatInt(new BigInteger("909999")));
		System.out.println(formatInt(new BigInteger("90909999")));
		System.out.println(formatInt(new BigInteger("900090019001921")));
		System.out.println(formatInt(new BigInteger("900090009000")));
		System.out.println(formatInt(new BigInteger("90909000")));
		System.out.println(formatInt(new BigInteger("90999009")));
		System.out.println(formatInt(new BigInteger("909009009")));
		System.out.println(formatInt(new BigInteger("9009909009009")));
		System.out.println(formatInt(new BigInteger("9009009909009009")));
		System.out.println(formatSmall(78));
		System.out.println(format(9999990999999.99));
		System.out.println(format(9999990999999.00));
	}

}