code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks.naming;
  
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Checks that pattern variable names conform to a specified pattern.
   * </p>
   * <ul>
   * <li>
   * Property {@code format} - Specifies valid identifiers.
   * Type is {@code java.util.regex.Pattern}.
   * Default value is {@code "^[a-z][a-zA-Z0-9]*$"}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name="PatternVariableName"/&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * class MyClass {
   *     MyClass(Object o1){
   *         if (o1 instanceof String STRING) { // violation, name 'STRING' must
   *                                            // match pattern '^[a-z][a-zA-Z0-9]*$'
   *         }
   *         if (o1 instanceof Integer num) { // OK
   *         }
   *     }
   * }
   * </pre>
   * <p>
   * An example of how to configure the check for names that have a lower case letter, followed by
   * letters and digits, optionally separated by underscore:
   * </p>
   * <pre>
   * &lt;module name="PatternVariableName"&gt;
   *   &lt;property name="format" value="^[a-z](_?[a-zA-Z0-9]+)*$"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * class MyClass {
   *     MyClass(Object o1){
   *         if (o1 instanceof String STR) { // violation, name 'STR' must
   *                                         // match pattern '^[a-z](_?[a-zA-Z0-9]+)*$'
   *         }
   *         if (o1 instanceof Integer num) { // OK
   *         }
   *         if (o1 instanceof Integer num_1) { // OK
   *         }
   *     }
   * }
   * </pre>
   * <p>
   * An example of how to configure the check to that all variables have 3 or more chars in name:
   * </p>
   * <pre>
   * &lt;module name="PatternVariableName"&gt;
   *   &lt;property name="format" value="^[a-z][_a-zA-Z0-9]{2,}$"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * class MyClass {
   *     MyClass(Object o1){
   *         if (o1 instanceof String s) { // violation, name 's' must
   *                                       // match pattern '^[a-z][_a-zA-Z0-9]{2,}$'
   *         }
   *         if (o1 instanceof Integer num) { // OK
   *         }
   *     }
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code name.invalidPattern}
   * </li>
   * </ul>
   *
   * @since 8.36
   */
  public class PatternVariableNameCheck extends AbstractNameCheck {
  
      /** Creates a new {@code PatternVariableNameCheck} instance. */
      public PatternVariableNameCheck() {
          super("^[a-z][a-zA-Z0-9]*$");
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.PATTERN_VARIABLE_DEF,
          };
      }
  
      @Override
      protected final boolean mustCheckName(DetailAST ast) {
          return true;
      }
  }
  