Format

Consider a Scala string that has values in it. For example, with "10 cats" we have the value 10, and some following text. With format we can generate this text.

With Java we have standard string format insertion points like "%d" for an Int. In Scala 3.3 we keep the same format codes.

Format example

Let us begin with a simple example. We have a number 10 (specified with the val keyword). We call format() with this Int.

Tip The formatted() method can be called on any object—so we can use it on an Int, Double or String value.

Here We pass a special format string to the formatted method. This uses the same format as String.format in Java.

object Program {
    def main(args: Array[String]): Unit = {
        val number = 10

        // Use a format string.
        val result = "There are %d cats.".format(number)
        println(result)
    }
}
There are 10 cats.

Format method

This is called on a format string. We pass it arguments that are placed in the format insertion codes. Here we insert an Int and a floating-point (Double) with "%d" and "%f."

object Program {
    def main(args: Array[String]): Unit = {
        // An example format string.
        val f = "I have %d dogs that weigh on average %f pounds."

        // An Int and Double for the format string.
        val count = 4
        val averageWeight = 14.5

        // Call format on the format string and print the result.
        val result = f.format(count, averageWeight)
        println(result)
    }
}
I have 4 dogs that weigh on average 14.500000 pounds.

Padding

Here we apply right and left padding to Ints and strings to justify text. For padding, we use the "-10s" and "10s" format codes for right and left padding insertions.

Note The "%1" and "%2" codes refer to the first and second arguments passed to the format method.

Detail The format method accepts the same format codes as the Java String.format method.

object Program {
    def main(args: Array[String]): Unit = {
        val lefts = List(10, 200, 3000)
        val rights = List("cat", "fish", "elephant")

        // Loop over indexes.
        for (i <- 0.until(lefts.length)) {
            // Get element from each list at this index.
            val left = lefts(i)
            val right = rights(i)

            // Use this format string.
            val padding = "%1$-10s %2$10s"

            // Call format to apply padding.
            val result = padding.format(left, right)
            println(result)
        }
    }
}10                cat
200              fish
3000         elephant

Reorder, repeat values

We can use a format string and the format() method to reorder and repeat values in a string. Consider this example. We have 3 insertions.

And The second argument to format, "cat," is repeated twice. The first argument "frog" is inserted after the second.

object Program {
    def main(args: Array[String]): Unit = {
        // Specify the second argument is placed first.
        // ... We can reorder and repeat arguments.
        val result = "%2$s %1$s %2$s".format("frog", "cat")
        println(result)
    }
}
cat frog cat

Formatting strings in Scala is done in a standard way (with the same literal syntax as Java). But with format() we can format values in a clearer way—with just a method call.