Method to Insert Commas into Large Numbers

Question

Is there a method that already exists and if not can a method be written that can format large numbers and insert commas into them?

100     = 100
1000    = 1,000  
10000   = 10,000
100000  = 100,000
1000000 = 1,000,000


public String insertCommas(Integer largeNumber) {

}

Answer 1

With NumberFormat you can do this easily:

NumberFormat format = NumberFormat.getInstance(Locale.US);

System.out.println(format.format(100));
System.out.println(format.format(1000));
System.out.println(format.format(1000000));

will ouput:

100
1,000
1,000,000

Answer 2

You can use NumberFormat#getNumberInstance with Locale.US:

A Locale object represents a specific geographical, political, or cultural region. An operation that requires a Locale to perform its task is called locale-sensitive and uses the Locale to tailor information for the user. For example, displaying a number is a locale-sensitive operation— the number should be formatted according to the customs and conventions of the user's native country, region, or culture.

---

System.out.println(NumberFormat.getNumberInstance(Locale.US).format(10000000));

This will print:

10,000,000

Side note: In Java 7, you can write an int with underscores: 1_000_000.