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 class type parameter 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]$"}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name="ClassTypeParameterName"/&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * class MyClass1&lt;T&gt; {}        // OK
   * class MyClass2&lt;t&gt; {}        // violation
   * class MyClass3&lt;abc&gt; {}      // violation
   * class MyClass4&lt;LISTENER&gt; {} // violation
   * class MyClass5&lt;RequestT&gt; {} // violation
   * </pre>
   * <p>
   * To configure the check for names that are uppercase word:
   * </p>
   * <pre>
   * &lt;module name="ClassTypeParameterName"&gt;
   *   &lt;property name="format" value="^[A-Z]{2,}$"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * class MyClass1&lt;T&gt; {}        // violation
   * class MyClass2&lt;t&gt; {}        // violation
   * class MyClass3&lt;abc&gt; {}      // violation
   * class MyClass4&lt;LISTENER&gt; {} // OK
   * class MyClass5&lt;RequestT&gt; {} // violation
   * </pre>
   * <p>
   * To configure the check for names that are camel case word with T as suffix (
   * <a href="https://checkstyle.org/styleguides/google-java-style-20180523/javaguide.html#s5.2.8-type-variable-names">
   * Google Style</a>):
   * </p>
   * <pre>
   * &lt;module name="ClassTypeParameterName"&gt;
   *   &lt;property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Example:</p>
   * <pre>
   * class MyClass1&lt;T&gt; {}        // violation
   * class MyClass2&lt;t&gt; {}        // violation
   * class MyClass3&lt;abc&gt; {}      // violation
   * class MyClass4&lt;LISTENER&gt; {} // violation
   * class MyClass5&lt;RequestT&gt; {} // 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 5.0
   */
  public class ClassTypeParameterNameCheck
      extends AbstractNameCheck {
  
      /** Creates a new {@code ClassTypeParameterNameCheck} instance. */
      public ClassTypeParameterNameCheck() {
          super("^[A-Z]$");
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public final int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.TYPE_PARAMETER,
          };
      }
  
      @Override
      protected final boolean mustCheckName(DetailAST ast) {
          final DetailAST location =
              ast.getParent().getParent();
          return location.getType() == TokenTypes.CLASS_DEF;
      }
  
  }
  