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Avoid String Concatenation


This is “string concatenation,” and it is a bad practice:

// bad practice, don't reuse!
String text = "Hello, " + name + "!";

Why? Some may say that it is slow, mostly because parts of the resulting string are copied multiple times. Indeed, on every + operator, String class allocates a new block in memory and copies everything it has into it; plus a suffix being concatenated. This is true, but this is not the point here.

Actually, I don’t think performance in this case is a big issue. Moreover, there were multiple experiments showing that concatenation is not that slow when compared to other string building methods and sometimes is even faster.

Some say that concatenated strings are not localizable because in different languages text blocks in a phrase may be positioned in a different order. The example above can’t be translated to, say, Russian, where we would want to put a name in front of “привет.” We will need to localize the entire block of code, instead of just translating a phrase.

However, my point here is different. I strongly recommend avoiding string concatenation because it is less readable than other methods of joining texts together.

Let’s see these alternative methods. I’d recommend three of them (in order of preference): String.format(), Apache StringUtils and Guava Joiner.

There is also a StringBuilder, but I don’t find it as attractive as StringUtils. It is a useful builder of strings, but not a proper replacer or string concatenation tool when readability is important.


String.format() is my favorite option. It makes text phrases easy to understand and modify. It is a static utility method that mirrors sprintf() from C. It allows you to build a string using a pattern and substitutors:

String text = String.format("Hello, %s!", name);

When the text is longer, the advantages of the formatter become much more obvious. Look at this ugly code:

String msg = "Dear " + customer.name()
  + ", your order #" + order.number()
  + " has been shipped at " + shipment.date()
  + "!";

This one looks much more beautiful doesn’t it (jSparrow even has a rule for this):

String msg = String.format(
  "Dear %1$s, your order #%2$d has been shipped at %3$tR!",
  customer.name(), order.number(), shipment.date()

Please note that I’m using argument indexes in order to make the pattern even more localizable. Let’s say, I want to translate it to Greek. This is how will it look:

Αγαπητέ %1$s, στις %3$tR στείλαμε την παραγγελία σου με αριθμό #%2$d!

I’m changing the order of substitutions in the pattern, but not in the actual list of methods arguments.

Apache StringUtils.join()

When the text is rather long (longer than your screen width), I would recommend that you use the utility class StringUtils from Apache commons-lang3:

import org.apache.commons.lang3.StringUtils;
String xml = StringUtils.join(
  "<?xml version='1.0'?>",
  "<p>This is a test XHTML document,",
  " which would look ugly,",
  " if we would use a single line,"
  " or string concatenation or String format().</p>"

The need to include an additional JAR dependency to your classpath may be considered a downside with this method (get its latest versions in Maven Central):


Guava Joiner

Similar functionality is provided by Joiner from Google Guava:

import com.google.common.base.Joiner;
String text = Joiner.on('').join(

It is a bit less convenient than StringUtils since you always have to provide a joiner (character or a string placed between text blocks).

Again, a dependency is required in this case:


Yes, in most cases, all of these methods work slower than a plain simple concatenation. However, I strongly believe that computers are cheaper than people. What I mean is that the time spent by programmers understanding and modifying ugly code is much more expensive than a cost of an additional server that will make beautifully written code work faster.

If you know any other methods of avoiding string concatenation, please comment below.

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