たまに忘れるのでここでメモ。
import java.text.*; import java.util.*; public class C{ public static void main(String[] args) throws Exception{ int intValue = 1018976; String stringValue = "1,018,976"; NumberFormat formatter = NumberFormat.getIntegerInstance(Locale.JAPAN); System.out.println(formatter.format(i)); System.out.println(formatter.parse(s)); } }