Adding comma in between every 3 digits to a large number in Java

The Java class below demontrates:
Adding comma in between every 3 digits to a large number by parsing the number string.
Adding comma in between every 3 digits to a large number by using regex.
Adding comma in between every 3 digits to a large number by using DecimalFormat.
Using System.nanoTime() and System.currentTimeMillis() to calculate the time it takes to process 999999 numbers.
The result shows the method that adds the comma to a number by parsing the number string is the most efficient one.
Note: Each of the three methods takes a string and assumes the string contains only digits, negative sign, postive sign and period.
[code language=”java”]
import java.text.DecimalFormat;
import java.util.Random;

public class NumberCommafy {

private final static int SIZE=999999;//Number of numbers to be generated.
private final static int MIN=10000000;//minimum number of each generated number.

//Adding comma in between every 3 digits to a large number by parsing the number string.
private static String stringParserCommafy(String inputNum) {

String commafiedNum="";
Character firstChar= inputNum.charAt(0);

//If there is a positive or negative number sign,
//then put the number sign to the commafiedNum and remove the sign from inputNum.
if(firstChar==’+’ || firstChar==’-‘)
{
commafiedNum = commafiedNum + Character.toString(firstChar);
inputNum=inputNum.replaceAll("[-\\+]", "");
}

//If the input number has decimal places,
//then split it into two, save the first part to inputNum
//and save the second part to decimalNum which will be appended to the final result at the end.
String [] splittedNum = inputNum.split("\\.");
String decimalNum="";
if(splittedNum.length==2)
{
inputNum=splittedNum[0];
decimalNum="."+splittedNum[1];
}

//The main logic for adding commas to the number.
int numLength = inputNum.length();
for (int i=0; i<numLength; i++) {
if ((numLength-i)%3 == 0 && i != 0) {
commafiedNum += ",";
}
commafiedNum += inputNum.charAt(i);
}

return commafiedNum+decimalNum;
}

//Adding comma in between every 3 digits to a large number by using regex.
private static String regexCommafy(String inputNum)
{
String regex = "(\\d)(?=(\\d{3})+$)";
String [] splittedNum = inputNum.split("\\.");
if(splittedNum.length==2)
{
return splittedNum[0].replaceAll(regex, "$1,")+"."+splittedNum[1];
}
else
{
return inputNum.replaceAll(regex, "$1,");
}
}

//Adding comma in between every 3 digits to a large number by using DecimalFormat.
private static String decimalFormatCommafy(String inputNum)
{
//If the input number has decimal places,
//then split it into two, save the first part to inputNum
//and save the second part to decimalNum which will be appended to the final result at the end.
String [] splittedNum = inputNum.split("\\.");
String decimalNum="";
if(splittedNum.length==2)
{
inputNum=splittedNum[0];
decimalNum="."+splittedNum[1];
}

Double inputDouble=Double.parseDouble(inputNum);
DecimalFormat myFormatter = new DecimalFormat("###,###");
String output = myFormatter.format(inputDouble);

return output+decimalNum;
}

private static String [] generateRandomNums()
{
String [] numbers = new String[SIZE];
Random rand = new Random();
for(int i=0; i<numbers.length;i++)
{
numbers[i]=String.valueOf(rand.nextInt(MIN) + MIN);
}

return numbers;
}

public static void main(String args[])
{
String [] numbers =
{
"+123456",
"1234567",
"-100000000",
"+2345676558947589.2546815"};

System.out.println("<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<Just a test>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
for(int i =0; i<numbers.length; i++)
{
System.out.println(stringParserCommafy(numbers[i]));
System.out.println(regexCommafy(numbers[i]));
System.out.println(decimalFormatCommafy(numbers[i]));
}

String [] nums = generateRandomNums();
System.out.println("<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<"+SIZE+" numbers has be generated, start commafy the numbers>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");

long startTime = System.nanoTime();
for(int i =0; i<nums.length; i++)
{
stringParserCommafy(nums[i]);
}
long endTime = System.nanoTime();
long stringParserCommafyTotalTime = (endTime – startTime)/1000000;
System.out.println("stringParserCommafy took " + stringParserCommafyTotalTime + " milliseconds.");

startTime = System.currentTimeMillis();
for(int i =0; i<nums.length; i++)
{
regexCommafy(nums[i]);
}
endTime = System.currentTimeMillis();
long regexCommafyTotalTime = endTime – startTime;
System.out.println("regexCommafy took "+regexCommafyTotalTime+" milliseconds.");

startTime = System.currentTimeMillis();
for(int i =0; i<nums.length; i++)
{
decimalFormatCommafy(nums[i]);
}
endTime = System.currentTimeMillis();
long decimalFormatCommafyTotalTime = endTime – startTime;
System.out.println("decimalFormatCommafy took "+decimalFormatCommafyTotalTime+" milliseconds.");

long winner=Math.min(Math.min(stringParserCommafyTotalTime, regexCommafyTotalTime), decimalFormatCommafyTotalTime);

if(winner==stringParserCommafyTotalTime)
{
System.out.println("!!!!!!!!stringParserCommafy runs the fastest!!!!!!!!");
}
else if(winner==regexCommafyTotalTime)
{
System.out.println("!!!!!!!!regexCommafy runs the fastest!!!!!!!!");
}
else
{
System.out.println("!!!!!!!!decimalFormatCommafy runs the fastest!!!!!!!!");
}
}

}
[/code]

A sample output of the above Java program.
[code language=”text”]
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<Just a test>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
+123,456
+123,456
123,456
1,234,567
1,234,567
1,234,567
-100,000,000
-100,000,000
-100,000,000
+2,345,676,558,947,589.2546815
+2,345,676,558,947,589.2546815
2,345,676,558,947,589.2546815
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<999999 numbers has be generated, start commafy the numbers>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
stringParserCommafy took 1084 milliseconds.
regexCommafy took 2337 milliseconds.
decimalFormatCommafy took 1950 milliseconds.
!!!!!!!!stringParserCommafy runs the fastest!!!!!!!!
[/code]