We discussed predefined character classes and Unicode character classes in Chapter 2, Understanding the Core Concepts of Java Regular Expressions. We need to make good use of it. So use \d instead of [0-9] or \D instead of [^0-9], and use \w instead of [a-zA-Z_0-9] or \W instead of [^a-zA-Z_0-9].
Use predefined character classes instead of longer versions
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