How to center a string using String.format?

Question

public class Divers {
  public static void main(String args[]){

     String format = \"|%1$-10s|%2$-10s|%3$-20s|\\n\";
     System.out.format(format, \"FirstName\",         


        

Answer 1

Here's another example. Allows you to choose how you want to treat the center when there is a different number of padding characters added to the beginning and end of the string.

Uses Java 11 String::repeat.

public class Strings {

    public enum Lean {
        START,
        END
    }

    public static String center(String value, int targetLength, Lean lean) {
        return center(value, targetLength, lean, ' ');
    }

    private static String center(String value, int targetLength, Lean lean, char pad) {

        if (targetLength < 1) {
            throw new IllegalArgumentException("Cannot center something into less than one space.");
        }

        int sourceLength = value.length();

        if (sourceLength == targetLength) {
            return value;
        }

        int paddingToAdd = targetLength - sourceLength;
        int half = paddingToAdd / 2;
        String spad = Character.toString(pad);
        String padding = spad.repeat(half);
        String startExtra = "";
        String endExtra = "";

        if (paddingToAdd % 2 == 1) {
            if (lean == Lean.START) {
                endExtra = spad;
            } else {
                startExtra = spad;
            }
        }

        return padding + startExtra + value + endExtra + padding;
    }
}



public class StringsTest {

    @Test
    public void centerAbcIn9LeanStart() {
        doTest(
                "abc",
                9,
                Strings.Lean.START,
                "   abc   "
        );
    }

    @Test
    public void centerAbcIn9LeanEnd() {
        doTest(
                "abc",
                9,
                Strings.Lean.END,
                "   abc   "
        );
    }

    @Test
    public void centerAbcIn10LeanStart() {
        doTest(
                "abc",
                10,
                Strings.Lean.START,
                "   abc    "
        );
    }

    @Test
    public void centerAbcIn10LeanEnd() {
        doTest(
                "abc",
                10,
                Strings.Lean.END,
                "    abc   "
        );
    }

    @Test
    public void centerAbcdIn9LeanStart() {
        doTest(
                "abcd",
                9,
                Strings.Lean.START,
                "  abcd   "
        );
    }

    @Test
    public void centerAbcdIn9LeanEnd() {
        doTest(
                "abcd",
                9,
                Strings.Lean.END,
                "   abcd  "
        );
    }

    @Test
    public void centerAbcdIn10LeanStart() {
        doTest(
                "abcd",
                10,
                Strings.Lean.START,
                "   abcd   "
        );
    }

    @Test
    public void centerAbcdIn10LeanEnd() {
        doTest(
                "abcd",
                10,
                Strings.Lean.START,
                "   abcd   "
        );
    }

    @Test
    public void centerAIn1LeanStart() {
        doTest(
                "a",
                1,
                Strings.Lean.START,
                "a"
        );
    }

    @Test
    public void centerAIn1LeanEnd() {
        doTest(
                "a",
                1,
                Strings.Lean.END,
                "a"
        );
    }

    @Test
    public void centerAIn2LeanStart() {
        doTest(
                "a",
                2,
                Strings.Lean.START,
                "a "
        );
    }

    @Test
    public void centerAIn2LeanEnd() {
        doTest(
                "a",
                2,
                Strings.Lean.END,
                " a"
        );
    }

    @Test
    public void centerAIn3LeanStart() {
        doTest(
                "a",
                3,
                Strings.Lean.START,
                " a "
        );
    }

    @Test
    public void centerAIn3LeanEnd() {
        doTest(
                "a",
                3,
                Strings.Lean.END,
                " a "
        );
    }

    @Test
    public void centerAbIn3LeanStart() {
        doTest(
                "ab",
                3,
                Strings.Lean.START,
                "ab "
        );
    }

    @Test
    public void centerAbIn3LeanEnd() {
        doTest(
                "ab",
                3,
                Strings.Lean.END,
                " ab"
        );
    }

    public void doTest(String value, int targetLength, Strings.Lean lean, String expected) {

        assertThat(
                "Test setup error: targetLength != expected.length()",
                targetLength,
                equalTo(expected.length()));

        assertThat(
                "Test setup error: value != expected.trim()",
                value,
                equalTo(expected.trim()));

        String actual = Strings.center(value, targetLength, lean);
        assertThat(actual, equalTo(expected));
    }
}