String.format()

Examples

The main placeholders:

void main() {
    String s = String.format("%s is %d years old", "Anna", 30);
    IO.println(s);
}

Output:

Anna is 30 years old

Decimal numbers: %.2f rounds to two places, and the locale sets the separator:

void main() {
    IO.println(String.format(Locale.ROOT, "Price: %.2f", 9.5));
    IO.println(String.format(Locale.GERMANY, "Price: %.2f", 9.5));
    IO.println(String.format(Locale.ROOT, "%,d", 1234567));
}

Output:

Price: 9.50
Price: 9,50
1,234,567

Field width and alignment — a table:

void main() {
    IO.println(String.format("%-8s|%6d|", "apples", 12));
    IO.println(String.format("%-8s|%6d|", "kiwi", 150));
    IO.println(String.format("%05d", 42));
}

Output:

apples  |    12|
kiwi    |   150|
00042

Notes

Common patterns: %.2f gives two decimal places, %10s a width of 10 aligned right, %-10s aligned left, %,d thousands separators, %x hexadecimal, %% a percent sign itself.

Without a locale argument the decimal separator comes from the system language: on a German or Russian computer %.2f gives 9,50. To always get a dot, pass Locale.ROOT as the first argument. If a value does not fit the placeholder (%d for a string), you get IllegalFormatConversionException.