java - String.format() to fill a string?

Question

I need to fill a String to a certain length with dashes, like:

cow-----8
cow-----9
cow----10
...
cow---100

the total length of the string needs to be 9. The prefix "cow" is constant. I'm iterating up to an input number. I can do this in an ugly way:

String str = "cow";
for (int i = 0; i < 1000; i++) {
    if (i < 10) {
        str += "-----";
    } 
    else if (i < 100) {
        str += "----";
    }
    else if (i < 1000) {
        str += "---";
    }
    else if (i < 10000) {
        str += "--";
    }
    str += i;
}

can I do the same thing more cleanly with string format?

Thanks

Answer 1

    int[] nums = { 1, 12, 123, 1234, 12345, 123456 };
    for (int num : nums) {
        System.out.println("cow" + String.format("%6d", num).replace(' ', '-'));
    }

This prints:

cow-----1
cow----12
cow---123
cow--1234
cow-12345
cow123456

The key expression is this:

String.format("%6d", num).replace(' ', '-')

This uses String.format, digit conversion, width 6 right justified padding with spaces. We then replace each space (if any) with dash.

Optionally, since the prefix doesn't contain any space in this particular case, you can bring the cow in:

String.format("cow%6d", num).replace(' ', '-')

See also

• java.util.Formatter - for full formatting syntax