How to format strings in Java
Primitive question, but how do I format strings like this:
"Step {1} of {2}"
by substituting variables using Java? In C# it's easy.
Take a look at String.format. Note, however, that it takes format specifiers similar to those of C's printf family of functions -- for example:
String.format("Hello %s, %d", "world", 42);
Would return "Hello world, 42". You may find this helpful when learning about the format specifiers. Andy Thomas-Cramer was kind enough to leave this link in a comment below, which appears to point to the official spec. The most commonly used ones are:
- %s - insert a string
- %d - insert a signed integer (decimal)
- %f - insert a real number, standard notation
This is radically different from C#, which uses positional references with an optional format specifier. That means that you can't do things like:
String.format("The {0} is repeated again: {0}", "word");
... without actually repeating the parameter passed to printf/format. (see The Scrum Meister's comment below)
If you just want to print the result directly, you may find System.out.printf (PrintStream.printf) to your liking.
In addition to String.format, also take a look java.text.MessageFormat. The format less terse and a bit closer to the C# example you've provided and you can use it for parsing as well.
For example:
int someNumber = 42;
String someString = "foobar";
Object[] args = {new Long(someNumber), someString};
MessageFormat fmt = new MessageFormat("String is \"{1}\", number is {0}.");
System.out.println(fmt.format(args));
A nicer example takes advantage of the varargs and autoboxing improvements in Java 1.5 and turns the above into a one-liner:
MessageFormat.format("String is \"{1}\", number is {0}.", 42, "foobar");
MessageFormat is a little bit nicer for doing i18nized plurals with the choice modifier. To specify a message that correctly uses the singular form when a variable is 1 and plural otherwise, you can do something like this:
String formatString = "there were {0} {0,choice,0#objects|1#object|1<objects}";
MessageFormat fmt = new MessageFormat(formatString);
fmt.format(new Object[] { new Long(numberOfObjects) });