Text blocks and formatting

Multi-line text and neat number output are common tasks. For the first, Java has text blocks; for the second, template-based formatting.

A text block

A text block starts with three quotes """ and a line break, and ends with three quotes. Line breaks inside are kept, and regular quotes need no escaping:

void main() {
    String poem = """
        Roses are red,
        Violets are blue,
        "Java" is great!
        """;
    IO.print(poem);
}

Output:

Roses are red,
Violets are blue,
"Java" is great!

Java removes the common indentation on the left by itself: it is measured from the leftmost line and the position of the closing """.

Indentation inside a block

Extra indentation of individual lines is kept. This is handy for JSON, HTML and SQL right in the code:

void main() {
    String json = """
        {
          "name": "Anna",
          "age": 30
        }""";
    IO.println(json);
}

Output:

{
  "name": "Anna",
  "age": 30
}

Here the closing quotes come right after }, so there is no line break at the end of the block.

formatted and String.format

The formatted() method fills values into a template. In the template, %s marks a place for a string, %d for a whole number, and %.2f for a fractional number with two decimal places:

void main() {
    String name = "Oleg";
    int cups = 3;
    double total = 10.5;
    String text = "%s ordered %d cups for $%.2f".formatted(name, cups, total);
    IO.println(text);
}

Output:

Oleg ordered 3 cups for $10.50

String.format(template, values) does the same. Note that the decimal separator follows the system's regional settings: an English locale uses a dot, while a German or Russian one prints 10,50.

printf

System.out.printf() formats and prints at once. A line break in the template is written as %n:

void main() {
    System.out.printf("Item: %s, price: %.1f%n", "tea", 2.456);
    System.out.printf("%d%% done%n", 75);
}

Output:

Item: tea, price: 2.5
75% done

%.1f rounds to one decimal place. To print the percent sign itself, double it: %%.

Field width

A number between % and the letter sets the minimum width. By default the value is right-aligned, and a minus sign left-aligns it. That is how you get even tables:

void main() {
    String format = "%-10s|%6d%n";
    System.out.printf(format, "Apples", 12);
    System.out.printf(format, "Pears", 7);
    System.out.printf(format, "Oranges", 150);
}

Output:

Apples    |    12
Pears     |     7
Oranges   |   150

Common mistake

No text may follow the opening """ on the same line — a line break must come right after it:

void main() {
    String text = """Hello,
        world""";
    IO.println(text);
}

Output (the first error; the compiler then prints four more that follow from it):

Main.java:2: error: illegal text block open delimiter sequence, missing line terminator
    String text = """Hello,
                     ^

Start the block's content on the next line.