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  1. PO
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    <p>I believe the answer might have already been determined, but I post to share the code.</p> <p>Short answer, if pure concatenation is all you are looking for, is: String.concat(...)</p> <p><strong>Output:</strong></p> <pre><code>ITERATION_LIMIT1: 1 ITERATION_LIMIT2: 10000000 s1: STRING1-1111111111111111111111 s2: STRING2-2222222222222222222222 iteration: 1 null: 1.7 nanos s1.concat(s2): 106.1 nanos s1 + s2: 251.7 nanos new StringBuilder(s1).append(s2).toString(): 246.6 nanos new StringBuffer(s1).append(s2).toString(): 404.7 nanos String.format("%s%s", s1, s2): 3276.0 nanos Tests complete </code></pre> <p><strong>Sample Code:</strong></p> <pre><code>package net.fosdal.scratch; public class StringConcatenationPerformance { private static final int ITERATION_LIMIT1 = 1; private static final int ITERATION_LIMIT2 = 10000000; public static void main(String[] args) { String s1 = "STRING1-1111111111111111111111"; String s2 = "STRING2-2222222222222222222222"; String methodName; long startNanos, durationNanos; int iteration2; System.out.println("ITERATION_LIMIT1: " + ITERATION_LIMIT1); System.out.println("ITERATION_LIMIT2: " + ITERATION_LIMIT2); System.out.println("s1: " + s1); System.out.println("s2: " + s2); int iteration1 = 0; while (iteration1++ &lt; ITERATION_LIMIT1) { System.out.println(); System.out.println("iteration: " + iteration1); // method #0 methodName = "null"; iteration2 = 0; startNanos = System.nanoTime(); while (iteration2++ &lt; ITERATION_LIMIT2) { method0(s1, s2); } durationNanos = System.nanoTime() - startNanos; System.out.println(String.format("%50s: %6.1f nanos", methodName, ((double) durationNanos) / ITERATION_LIMIT2)); // method #1 methodName = "s1.concat(s2)"; iteration2 = 0; startNanos = System.nanoTime(); while (iteration2++ &lt; ITERATION_LIMIT2) { method1(s1, s2); } durationNanos = System.nanoTime() - startNanos; System.out.println(String.format("%50s: %6.1f nanos", methodName, ((double) durationNanos) / ITERATION_LIMIT2)); // method #2 iteration2 = 0; startNanos = System.nanoTime(); methodName = "s1 + s2"; while (iteration2++ &lt; ITERATION_LIMIT2) { method2(s1, s2); } durationNanos = System.nanoTime() - startNanos; System.out.println(String.format("%50s: %6.1f nanos", methodName, ((double) durationNanos) / ITERATION_LIMIT2)); // method #3 iteration2 = 0; startNanos = System.nanoTime(); methodName = "new StringBuilder(s1).append(s2).toString()"; while (iteration2++ &lt; ITERATION_LIMIT2) { method3(s1, s2); } durationNanos = System.nanoTime() - startNanos; System.out.println(String.format("%50s: %6.1f nanos", methodName, ((double) durationNanos) / ITERATION_LIMIT2)); // method #4 iteration2 = 0; startNanos = System.nanoTime(); methodName = "new StringBuffer(s1).append(s2).toString()"; while (iteration2++ &lt; ITERATION_LIMIT2) { method4(s1, s2); } durationNanos = System.nanoTime() - startNanos; System.out.println(String.format("%50s: %6.1f nanos", methodName, ((double) durationNanos) / ITERATION_LIMIT2)); // method #5 iteration2 = 0; startNanos = System.nanoTime(); methodName = "String.format(\"%s%s\", s1, s2)"; while (iteration2++ &lt; ITERATION_LIMIT2) { method5(s1, s2); } durationNanos = System.nanoTime() - startNanos; System.out.println(String.format("%50s: %6.1f nanos", methodName, ((double) durationNanos) / ITERATION_LIMIT2)); } System.out.println(); System.out.println("Tests complete"); } public static String method0(String s1, String s2) { return ""; } public static String method1(String s1, String s2) { return s1.concat(s2); } public static String method2(String s1, String s2) { return s1 + s2; } public static String method3(String s1, String s2) { return new StringBuilder(s1).append(s2).toString(); } public static String method4(String s1, String s2) { return new StringBuffer(s1).append(s2).toString(); } public static String method5(String s1, String s2) { return String.format("%s%s", s1, s2); } } </code></pre>
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    1. POWhat's the fastest way to concatenate two Strings in Java?
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    1. CONice comment. I've been looking for speed of string.format and now I see that it's little bit slow :-) I'll use concat instead.
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      1. USMartin Podval
 

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