You're not returning a String
, you're just printing one in the default system print stream.
Hence your code will not compile.
return String.format("+%d(%2$s)%3$s-%4$s-%5$s", 38,
String.format("%010d", 501234567).substring(0, 3),
String.format("%010d", 501234567).substring(3, 6),
String.format("%010d", 501234567).substring(6, 8),
String.format("%010d", 501234567).substring(8))