The quick and dirty way to concatenate strings in Java is to use the concatenation operator (+). This will yield a reasonable performance if you need to combine two or three strings (fixed-size). But if you want to concatenate n strings in a loop, the performance degrades in multiples of n. Given that String is immutable, for large number of string concatenation operations, using (+) will give us a worst performance. But how bad ? How StringBuffer, StringBuilder or String.concat() performs if we put them on a performance test ?. This article will try to answer those questions. We will be using Perf4J to calculate the performance, since this library will give us aggregated performance statistics like mean, minimum, maximum, standard deviation over a set time span. In the code, we will concatenate a string (*) repeatedly 50,000 times and this iteration will be performed 21 times so that we can get a good standard deviation. The following methods will be used to concatenate strings.