Learning Java, 4th Edition

Printf-Style Formatting

A standard feature that Java adopted from the C language is printf-style string formatting. printf-style formatting utilizes special format strings embedded into text to tell the formatting engine where to place arguments and give detailed specification about conversions, layout, and alignment. The printf formatting methods also make use of variable-length argument lists, which makes working with them much easier. Here is a quick example of printf-formatted output:

    System.out.printf( "My name is %s and I am %d years old\n", name, age );

The printf formatting draws its name from the C language printf() function, so if you’ve done any C programming, this will look familiar. Java has extended the concept, adding some additional type safety and convenience features. Although Java has had some text formatting capabilities in the past (we’ll discuss the java.text package and MessageFormat later), printf formatting was not really feasible until variable-length argument lists and autoboxing of primitive types were added in Java 5.0. (We mention this to explain why these similar APIs both exist in Java.)

Formatter

The primary new tool in our text formatting arsenal is the java.util.Formatter class and its format() method. Several convenience methods can hide the Formatter object from you and you may not need to create a Formatter directly. First, the static String.format() method can be used to format a String with arguments (like the C language sprintf() method):