The Scoreboard

Building text with a pattern

Every line you have printed so far was either fixed text or several pieces joined with +. A plus sign works, but it never gives any one piece a fixed width, so as soon as you care what a line looks like — not just what it says — gluing pieces together stops being enough.

String.format takes a pattern with slots marked by a percent sign, and a list of values to drop into those slots in order:

String player = "Ana";
int score = 12;
System.out.println(String.format("%s scored %d", player, score));

Ana scored 12

%s means "a piece of text goes here", %d means "a whole number goes here", and String.format builds one finished piece of text with both slots filled in. System.out.println then prints that one piece of text, exactly as it would print anything else.

Widths are what make a column

A fixed width is the whole trick behind a column, and you put the width number straight inside the slot:

• %-7s gives the name 7 characters. The - pushes it to the left, padding with spaces on the right until it fills the width — the way a label reads more naturally.
• %3d gives the score 3 characters, pushed to the right by default, padding on the left. That is why a two-digit score and a one-digit score both finish in the same column.

Put those together with an ordinary space and a plain %s for whatever should not be padded at all, and every row built from the same pattern lines up under the last, no matter how long any one value happens to be.

A worked example

A bird tally rather than a scoreboard, so the answer stays yours to write:

public class Main {
    public static void main(String[] args) {
        String bird = "Owl";
        int seen = 3;
        System.out.println("[" + bird + "][" + seen + "]");
        System.out.println(String.format("[%-6s][%4d]", bird, seen));

        bird = "Heron";
        seen = 14;
        System.out.println(String.format("[%-6s][%4d]", bird, seen));
    }
}

[Owl][3]
[Owl   ][   3]
[Heron ][  14]

The square brackets are there only to make the padding visible. The glued row hugs its values; the two below give every name six characters and every count four, so both closing brackets land in the same column, and so do both numbers.

Your turn

The editor holds a scoreboard with three players. Each gets a name, a score, and bar = "#".repeat(score), which makes one copy of # per point.

Press Run first. Ana and Ben come out as tidy rows; Cleo's row is ragged, because her line is still glued together with plus signs and nothing gives her values a fixed width:

System.out.println(player + " " + score + " " + bar);

Rewrite that one line using String.format, matching the pattern used by the two rows above it, so her row lines up with them. The widths you need are already on screen, in the two finished rows.

Then set her score to 11 and run it again: the bar grows, the row stays in column. Put the 5 back afterwards.

If something goes wrong

The likeliest slip is a missing %. If part of the row prints as literal letters like -7s rather than padded text, a % has gone missing from the front of a format specifier — String.format only treats the characters after a % as an instruction.

If the row prints in the wrong place, count the widths against the two rows above rather than guessing; one number different is all it takes to drift a column.

If a row goes missing entirely and nothing after it prints either, String.format was probably given fewer values than its pattern has slots for. Unlike a lot of Java mistakes, this one is caught only when the line runs, not when the program compiles.

Nothing here can break. Change a score, press Run, and read your own board.