Is there a way to build a Java String using an SLF4J-style formatting function?

For concatenating strings one time, the old reliable "str" + param + "other str" is perfectly fine (it's actually converted by the compiler into a StringBuilder).

StringBuilders are mainly useful if you have to keep adding things to the string, but you can't get them all into one statement. For example, take a for loop:

String str = "";
for (int i = 0; i < 1000000; i++) {
    str += i + " "; // ignoring the last-iteration problem
}

This will run much slower than the equivalent StringBuilder version:

StringBuilder sb = new StringBuilder(); // for extra speed, define the size
for (int i = 0; i < 1000000; i++) {
    sb.append(i).append(" ");
}
String str = sb.toString();

But these two are functionally equivalent:

String str = var1 + " " + var2;
String str2 = new StringBuilder().append(var1).append(" ").append(var2).toString();

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Having said all that, my actual answer is:

Check out java.text.MessageFormat. Sample code from the Javadocs:

int fileCount = 1273;
String diskName = "MyDisk";
Object[] testArgs = {new Long(fileCount), diskName};

MessageFormat form = new MessageFormat("The disk \"{1}\" contains {0} file(s).");

System.out.println(form.format(testArgs));

Output:

The disk "MyDisk" contains 1,273 file(s).

There is also a static format method which does not require creating a MessageFormat object.

All such libraries will boil down to string concatenation at their most basic level, so there won't be much performance difference from one to another.

Although the Accepted answer is good, if (like me) one is interested in exactly Slf4J-style semantics, then the correct solution is to use Slf4J's MessageFormatter

Here is an example usage snippet:

public static String format(String format, Object... params) {
    return MessageFormatter.arrayFormat(format, params).getMessage();
}

(Note that this example discards a last argument of type Throwable)