Text blocks and formatted text

Text blocks

Text of several lines, such as a ticket, has so far been many println calls, or one String full of \n. Since Java 15, a text block holds text of several lines as it looks. It starts with three double quotes and a line break, and ends with three double quotes:

String ticket = """
        FERRY TICKET
        From: Harbor A
        To:   Island Pier
          Deck seat 14
        """;
System.out.print(ticket);

FERRY TICKET
From: Harbor A
To:   Island Pier
  Deck seat 14

• The text starts on the line after the opening """. Nothing but spaces may follow the opening quotes on their line.
• The lines are indented to fit the code, and javac removes that indentation: it finds the line with the fewest spaces in front (lines with nothing else on them don't count), counting the line of the closing """ too, and removes that many spaces from every line. Here the closing quotes are as far in as FERRY TICKET, so FERRY TICKET starts at the left edge, and Deck seat 14, two spaces further in, keeps its two spaces.
• Since the closing """ is on a line of its own, the text ends with a line break, after Deck seat 14. That's why the example uses print: println would add a second line break, an empty line. Write the closing quotes right after the last word, Deck seat 14""";, for a text block without that last line break.
• A double quote inside a text block needs no backslash: Seat "14" can be written as it is. \n and \t still work, a backslash at the very end of a line joins it with the next one, and spaces at the end of a line are removed (write \s for a space that must stay).

Text on the line of the opening quotes doesn't compile:

public class Main {
    public static void main(String[] args) {
        String sign = """Closed
            today""";
        System.out.println(sign);
    }
}

Main.java:3: error: illegal text block open delimiter sequence, missing line terminator
        String sign = """Closed
                         ^
Main.java:4: error: illegal text block open delimiter sequence, missing line terminator
            today""";
                    ^
2 errors

A text block is an ordinary String once it's made: ticket.length(), ticket.split("\n") and the rest work as always.

String.format

Building a line from text and values with + gets hard to read when there are many of them. String.format takes a format, a String with places marked by %, and the values to put there, in order:

String name = "Ada";
int seat = 14;
double price = 23.5;
String line = String.format("%s sits in seat %d and paid %.2f euros", name, seat, price);
System.out.println(line);
System.out.printf("Seat %d of %d%n", seat, 120);

Ada sits in seat 14 and paid 23.50 euros
Seat 14 of 120

• %s puts a value as text (any value: a String, a number, an object's toString), %d a whole number, and %f a decimal number. %.2f rounds it to two decimals.
• System.out.printf formats and prints in one go. Unlike println, it adds no line break: %n in the format is one.
• Since Java 15, a String has the method formatted, which does the same with the String as the format: "Seat %d".formatted(seat). It goes well with a text block: write the text block with %s and %d in it, and call .formatted(...) on it.
• %% prints a percent sign.
• The decimal point follows the language settings of the computer: on Java Arena it's a point, but String.format("%.2f", 23.5) gives 23,50 on a computer set up for a language that writes a comma, such as German or Finnish.

A value of the wrong kind for its place is an error only when the program runs: %d with a double crashes.

public class Main {
    public static void main(String[] args) {
        double weight = 2.5;
        System.out.println(String.format("%d kg", weight));
    }
}

Exception in thread "main" java.util.IllegalFormatConversionException: d != java.lang.Double
	at Main.main(Main.java:4)

Columns

A number between the % and the letter is a width: the value takes at least that many characters, padded with spaces in front, so that it's right-aligned. A minus sign pads after the value instead, which aligns it left. %8.2f is a decimal number with two decimals in eight characters, %-10s a text left-aligned in ten, and %03d pads a whole number with zeros instead of spaces:

System.out.println(String.format("%-10s|%8.2f|", "tea", 3.5));
System.out.println(String.format("%-10s|%8.2f|", "cake", 12.25));
System.out.println(String.format("Locker %03d", 7));

tea       |    3.50|
cake      |   12.25|
Locker 007

Every line has its name in the same ten characters and its price in the same eight, so the columns line up, whatever the lengths. A value longer than its width isn't cut: it just takes more room.