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    <p>Just for fun, I have run this micro benchmark. The results of the last run (i.e. post JVM warm up / JIT) are below (results are fairly consistent from one run to another anyway):</p> <pre><code>regex with numbers 123 chars with numbers 33 parseInt with numbers 33 regex with words 123 chars with words 34 parseInt with words 733 </code></pre> <p>In other words, chars is very efficient, Integer.parseInt is as efficient as char IF the string is a number, but awfully slow if the string is not a number. Regex is in between.</p> <p><strong>Conclusion</strong></p> <p>If you parse a string into a number and you expect the string to be a number in general, using Integer.parseInt is the best solution (efficient and readable). The penalty you get when the string is not a number should be low if it is not too frequent.</p> <p>ps: my regex is maybe not optimal, feel free to comment.</p> <pre><code>public class TestNumber { private final static List&lt;String&gt; numbers = new ArrayList&lt;&gt;(); private final static List&lt;String&gt; words = new ArrayList&lt;&gt;(); public static void main(String args[]) { long start, end; Random random = new Random(); for (int i = 0; i &lt; 1000000; i++) { numbers.add(String.valueOf(i)); words.add(String.valueOf(i) + "x"); } for (int i = 0; i &lt; 5; i++) { start = System.nanoTime(); regex(numbers); System.out.println("regex with numbers " + (System.nanoTime() - start) / 1000000); start = System.nanoTime(); chars(numbers); System.out.println("chars with numbers " + (System.nanoTime() - start) / 1000000); start = System.nanoTime(); exception(numbers); System.out.println("exceptions with numbers " + (System.nanoTime() - start) / 1000000); start = System.nanoTime(); regex(words); System.out.println("regex with words " + (System.nanoTime() - start) / 1000000); start = System.nanoTime(); chars(words); System.out.println("chars with words " + (System.nanoTime() - start) / 1000000); start = System.nanoTime(); exception(words); System.out.println("exceptions with words " + (System.nanoTime() - start) / 1000000); } } private static int regex(List&lt;String&gt; list) { int sum = 0; Pattern p = Pattern.compile("[0-9]+"); for (String s : list) { sum += (p.matcher(s).matches() ? 1 : 0); } return sum; } private static int chars(List&lt;String&gt; list) { int sum = 0; for (String s : list) { boolean isNumber = true; for (char c : s.toCharArray()) { if (c &lt; '0' || c &gt; '9') { isNumber = false; break; } } if (isNumber) { sum++; } } return sum; } private static int exception(List&lt;String&gt; list) { int sum = 0; for (String s : list) { try { Integer.parseInt(s); sum++; } catch (NumberFormatException e) { } } return sum; } } </code></pre>
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    1. POJava regular expression offers any performance benefit?
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    1. COthrowing and catching an exception is typically a pretty expensive operation. If you're sure that the format is strictly digits with no grouping or decimal separators, using the char approach is probably the fastest you can achieve, though I would use Character.isDigit rather than if check you have above. If you need more robust support for grouping and decimal separators, you might do better off with a regex or a NumberFormat object.
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    2. CO*"throwing and catching an exception is typically a pretty expensive operation"* well yes but the point is that when the input is a number, parseInt is as fast and deals with things one might forget (sign etc). So it's more robust and as fast: no reason not to use it unless you know you will get many inputs that will throw an exception.
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    3. COI agree, that if you're not doing it for a large number of calls, parseInt is ok, although i'm not sure parseInt handles grouping separators and the like, which NumberFormat.parse() would.
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