Parameterized Strings in Java

Question

I find myself very frequently wanting to write reusable strings with parameter placeholders in them, almost exactly like what you'd find in an SQL PreparedStatement.

Here's an example:

private static final String warning = "You requested ? but were assigned ? instead.";

public void addWarning(Element E, String requested, String actual){

     warning.addParam(0, requested);
     warning.addParam(1, actual);
     e.setText(warning);
     //warning.reset() or something, I haven't sorted that out yet.
}

Does something like this exist already in Java? Or, is there a better way to address something like this?

What I'm really asking: is this ideal?

Community · Accepted Answer · 2017-05-23 11:46:25Z

92

`String.format()`

Since Java 5, you can use String.format to parametrize Strings. Example:

String fs;
fs = String.format("The value of the float " +
                   "variable is %f, while " +
                   "the value of the " + 
                   "integer variable is %d, " +
                   " and the string is %s",
                   floatVar, intVar, stringVar);

See http://docs.oracle.com/javase/tutorial/java/data/strings.html

Alternatively, you could just create a wrapper for the String to do something more fancy.

`MessageFormat`

Per the comment by Max and answer by Affe, you can localize your parameterized String with the MessageFormat class.

edited May 23, 2017 at 11:46

CommunityBot

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answered Apr 4, 2012 at 21:03

Garrett Hall

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2 Comments

JHarnach Over a year ago

I can't believe I overlooked this. Thanks Garrett!

Max Over a year ago

And use the MessageFormat class if you would like to format strings in a locale and language independent way.

Keith Randall · Accepted Answer · 2012-04-04 21:04:10Z

16

You could use String.format. Something like:

String message = String.format("You requested %2$s but were assigned %1$s", "foo", "bar");

will generate

"You requested bar but were assigned foo"

answered Apr 4, 2012 at 21:04

Keith Randall

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Comments

Affe · Accepted Answer · 2012-04-04 21:05:43Z

7

It is built-in, yes. The class you're looking for is java.text.MessageFormat

answered Apr 4, 2012 at 21:05

Affe

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1 Comment

Teodor Marinescu Over a year ago

In my opinion this is the right answer to this question. Thanks!

Michael Laffargue · Accepted Answer · 2022-12-05 15:54:53Z

3

Since Java 15, String has a method formatted equivalent to String.format.

So you can directly use "var1 is %s, var2 is %s".formatted(var1, var2);

Java documentation

answered Dec 5, 2022 at 15:54

Michael Laffargue

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Comments

kommradHomer · Accepted Answer · 2012-04-04 21:03:42Z

2

Java String formatter

answered Apr 4, 2012 at 21:03

kommradHomer

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Comments

Chris · Accepted Answer · 2012-04-05 18:51:33Z

1

The String class provides the following format method, http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/String.html. For example (as per the original post):

private final static String string = "You requested %s but were assigned %s instead.";

public void addWarning(Element e, String requested, String actual) {
String warning = String.format(string, requested, actual);
e.setText(warning);

edited Apr 5, 2012 at 18:51

answered Apr 4, 2012 at 21:43

Chris

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Comments

bn. · Accepted Answer · 2012-04-04 21:08:35Z

0

I would probably do something like:

private final String warning = String.format("You requested %s but were assigned %s instead.", requested, actual);

If you wanted to put the parameterized string before the call to format the string you could do something like what you see below, although this is less clear.

Neither of these solutions are inherently localizeable; you may want to consider something like a .properties file if you wish to support non-English locales.

private static final String warning = "You requested %s but were assigned %s instead.";

public void addWarning(Element E, String requested, String actual){
     e.setText(String.format(warning, requested, actual);
     //warning.reset() or something, I haven't sorted that out yet.
}

answered Apr 4, 2012 at 21:08

bn.

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1 Comment

JHarnach Over a year ago

localization may become relevant down the road, I hadn't considered that. Good point.

ratchet freak · Accepted Answer · 2012-04-04 21:17:00Z

0

the formatter can do this for you (with some extras as adding leading zeroes spacing things out and more)

private static final String warning = "You requested %1$s but were assigned %2$s instead.";

public void addWarning(Element E, String requested, String actual){
     Formatter f = new Formatter();//you'll need to recreate it each time
     try{
         f.format(warning,requested,actual);
         e.setText(f.out().toString());
    }finally{f.close();}

}

answered Apr 4, 2012 at 21:17

ratchet freak

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Comments

talnicolas · Accepted Answer · 2012-04-04 21:05:38Z

-2

Well if your String was final you sure wouldn't be able to modify it later. I don't know if maybe you could find a better use case for that kind of thing as you could simply do:

public void addWarning(Element E, String requested, String actual){

     String warning = "You requested" + requested + " but were assigned " + actual + " instead."     
     e.setText(warning);
}

answered Apr 4, 2012 at 21:05

talnicolas

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