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copied!<p>Probably a <code>replaceAll("(\\d)\\1+", "$1")</code></p> <ul> <li><code>$</code> plays a special role in a replacing string, designating the first capturing group.</li> <li><code>+</code> allows for replacing as many identical number as possible <code>(\\d)\\1</code> would only replace them by pair: <code>777xx</code> => <code>77xx</code> (thank you <a href="https://stackoverflow.com/users/12267/ben-doom">Ben Doom</a> for the remark)</li> </ul> <p>So:</p> <pre><code>System.out.println("77433211".replaceAll("(\\d)\\1+", "$1")); </code></pre> <p>will return</p> <pre><code>74321 </code></pre> <hr> <pre><code>String java.lang.String.replaceAll(String regex, String replacement) </code></pre> <p>Replaces each substring of this string that matches the given regular expression with the given replacement. </p> <p>An invocation of this method of the form <code>str.replaceAll(regex, repl)</code> yields exactly the same result as the expression </p> <pre><code>java.util.regex.Pattern.compile(regex).matcher(str).replaceAll(repl) </code></pre> <hr> <p><strong>Warning</strong>: <code>String.replaceAll()</code> function does not modify the String on which it is applied. It returns a modified String (or <em>a new String with the same content</em> if the pattern does not match anything)</p> <p>So you need to affect the result of a <code>replaceAll()</code> call to itself to actually update your String with the regexp changes.</p> <pre><code>String aString = "77433211" aString = aString.replaceAll("(\\d)\\1+", "$1")); </code></pre>

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