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copied!<p>You can't do this in Java regex. You'd have to manually post-process using <a href="http://java.sun.com/javase/6/docs/api/java/lang/String.html#toUpperCase%28%29" rel="noreferrer"><code>String.toUpperCase()</code></a> and <a href="http://java.sun.com/javase/6/docs/api/java/lang/String.html#toLowerCase()" rel="noreferrer"><code>toLowerCase()</code></a> instead.</p> <p>Here's an example of how you use regex to find and capitalize words of length at least 3 in a sentence </p> <pre><code> String text = "no way oh my god it cannot be"; Matcher m = Pattern.compile("\\b\\w{3,}\\b").matcher(text); StringBuilder sb = new StringBuilder(); int last = 0; while (m.find()) { sb.append(text.substring(last, m.start())); sb.append(m.group(0).toUpperCase()); last = m.end(); } sb.append(text.substring(last)); System.out.println(sb.toString()); // prints "no WAY oh my GOD it CANNOT be" </code></pre> <hr> <h3>Note on <code>appendReplacement</code> and <code>appendTail</code></h3> <p>Note that the above solution uses <code>substring</code> and manages a <code>tail</code> index, etc. In fact, you can go without these if you use <a href="http://java.sun.com/javase/6/docs/api/java/util/regex/Matcher.html#appendReplacement%28java.lang.StringBuffer,%20java.lang.String%29" rel="noreferrer"><code>Matcher.appendReplacement</code></a> and <code>appendTail</code>.</p> <pre><code> StringBuffer sb = new StringBuffer(); while (m.find()) { m.appendReplacement(sb, m.group().toUpperCase()); } m.appendTail(sb); </code></pre> <p>Note how <code>sb</code> is now a <a href="http://java.sun.com/javase/6/docs/api/java/lang/StringBuffer.html" rel="noreferrer"><code>StringBuffer</code></a> instead of <a href="http://java.sun.com/javase/6/docs/api/java/lang/StringBuilder.html" rel="noreferrer"><code>StringBuilder</code></a>. Until <code>Matcher</code> provides <code>StringBuilder</code> overloads, you're stuck with the slower <code>StringBuffer</code> if you want to use these methods.</p> <p>It's up to you whether the trade-off in less efficiency for higher readability is worth it or not.</p> <h3>See also</h3> <ul> <li><a href="https://stackoverflow.com/questions/355089/stringbuilder-and-stringbuffer-in-java"><code>StringBuilder</code> and <code>StringBuffer</code> in Java</a></li> </ul>

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