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copied!<p>Here's a solution that uses <a href="http://java.sun.com/javase/6/docs/api/java/util/Scanner.html" rel="nofollow noreferrer"><code>java.util.Scanner</code></a>:</p> <pre><code>Scanner sc = new Scanner("12+3 - 456").useDelimiter("\\b"); while (sc.hasNext()) { if (sc.hasNextInt()) { int num = sc.nextInt(); System.out.printf("Got an int [%s]%n", num); } else { String op = sc.next().trim(); System.out.printf("Got an op [%s]%n", op); } } </code></pre> <p>The above prints (<a href="http://ideone.com/MMvJn" rel="nofollow noreferrer">as seen on ideone.com</a>):</p> <pre><code>Got an int [12] Got an op [+] Got an int [3] Got an op [-] Got an int [456] </code></pre> <p>The delimiter is <code>\b</code> (the backslash doubled in a Java string literal), which is the "word boundary". It occurs, among other places, between word characters <code>\w</code> (which digits are) and non-word characters <code>\W</code> (which operators are).</p> <p>As a caveat, this delimiter regex will not properly tokenize floating point numbers with decimal points, but more specific regex can be written to address those issues should they be needed.</p> <p>Note also the convenience of using <code>Scanner</code> to parse the <code>String</code> into <code>int</code>; you can do this in such a way that it will never throw an exception (e.g. by first asserting that it <code>hasNextInt()</code>).</p> <h3>Related questions</h3> <ul> <li><a href="https://stackoverflow.com/questions/3059333/validating-input-using-java-util-scanner">Validating input using java.util.Scanner</a> - a quick <code>Scanner</code> tutorial</li> </ul> <h3>References</h3> <ul> <li><a href="http://www.regular-expressions.info/wordboundaries.html" rel="nofollow noreferrer">regular-expressions.info/Word Boundaries</a></li> </ul>

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