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;
  import com.puppycrawl.tools.checkstyle.utils.ScopeUtil;
  
  /**
   * <p>
   * Checks that local, non-{@code final} variable names conform to a specified pattern.
   * A catch parameter is considered to be
   * a local variable.
   * </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]*$"}.
   * </li>
   * <li>
   * Property {@code allowOneCharVarInForLoop} - Allow one character variable name in
   * <a href="https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html">
   * initialization expressions</a>
   * in FOR loop if one char variable name is prohibited by {@code format} regexp.
   * Type is {@code boolean}.
   * Default value is {@code false}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name="LocalVariableName"/&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * class MyClass {
   *   void MyMethod() {
   *     for (int var = 1; var &lt; 10; var++) {} // OK
   *     for (int VAR = 1; VAR &lt; 10; VAR++) {} // violation, name 'VAR' must match
   *                                           // pattern '^[a-z][a-zA-Z0-9]*$'
   *     for (int i = 1; i &lt; 10; i++) {} // OK
   *     for (int var_1 = 0; var_1 &lt; 10; var_1++) {} // violation, name 'var_1' must match
   *                                                    // pattern '^[a-z][a-zA-Z0-9]*$'
   *   }
   * }
   * </pre>
   * <p>
   * An example of how to configure the check for names that begin with a lower
   * case letter, followed by letters, digits, and underscores is:
   * </p>
   * <pre>
   * &lt;module name="LocalVariableName"&gt;
   *   &lt;property name="format" value="^[a-z](_?[a-zA-Z0-9]+)*$"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * class MyClass {
   *   void MyMethod() {
   *     for (int var = 1; var &lt; 10; var++) {} // OK
   *     for (int VAR = 1; VAR &lt; 10; VAR++) {} // violation, name 'VAR' must match
   *                                              // pattern '^[a-z](_?[a-zA-Z0-9]+)*$'
   *     for (int i = 1; i &lt; 10; i++) {} // OK
   *     for (int var_1 = 0; var_1 &lt; 10; var_1++) {} // OK
   *   }
   * }
   * </pre>
   * <p>
   * An example of one character variable name in
   * initialization expression(like "i") in FOR loop:
   * </p>
   * <pre>
   * for(int i = 1; i &lt; 10; i++) {}
   * for(int K = 1; K &lt; 10; K++) {}
   * List list = new ArrayList();
   * for (Object o : list) {}
   * for (Object O : list) {}
   * </pre>
   * <p>
   * An example of how to configure the check to allow one character variable name in
   * <a href="https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html">
   * initialization expressions</a> in FOR loop, where regexp allows 2 or more chars:
   * </p>
   * <pre>
   * &lt;module name="LocalVariableName"&gt;
   *   &lt;property name="format" value="^[a-z][_a-zA-Z0-9]+$"/&gt;
   *   &lt;property name="allowOneCharVarInForLoop" value="true"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * class MyClass {
   *   void MyMethod() {
   *     int good = 1;
   *     int g = 0; // violation
   *     for (int v = 1; v &lt; 10; v++) { // OK
   *         int a = 1; // violation
   *     }
   *     for (int V = 1; V &lt; 10; V++) { // OK
   *         int I = 1; // violation
   *     }
   *     List list = new ArrayList();
   *     for (Object o : list) { // OK
   *         String a = ""; // violation
   *     }
   *     for (Object O : list) { // OK
   *         String A = ""; // violation
   *     }
   *   }
   * }
   * </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="LocalVariableName"&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 {
   *   void MyMethod() {
   *     int goodName = 0;
   *     int i = 1; // violation
   *     for (int var = 1; var &lt; 10; var++) { //OK
   *       int j = 1; // violation
   *     }
   *   }
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code name.invalidPattern}
   * </li>
   * </ul>
   *
   * @since 3.0
   */
  public class LocalVariableNameCheck
      extends AbstractNameCheck {
  
      /**
       * Allow one character variable name in
       * <a href="https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html">
       * initialization expressions</a>
       * in FOR loop if one char variable name is prohibited by {@code format} regexp.
       */
      private boolean allowOneCharVarInForLoop;
  
      /** Creates a new {@code LocalVariableNameCheck} instance. */
      public LocalVariableNameCheck() {
          super("^[a-z][a-zA-Z0-9]*$");
      }
  
      /**
       * Setter to allow one character variable name in
       * <a href="https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html">
       * initialization expressions</a>
       * in FOR loop if one char variable name is prohibited by {@code format} regexp.
       *
       * @param allow Flag for allowing or not one character name in FOR loop.
       */
      public final void setAllowOneCharVarInForLoop(boolean allow) {
          allowOneCharVarInForLoop = allow;
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.VARIABLE_DEF,
          };
      }
  
      @Override
      protected final boolean mustCheckName(DetailAST ast) {
          final boolean result;
          if (allowOneCharVarInForLoop && isForLoopVariable(ast)) {
              final String variableName = ast.findFirstToken(TokenTypes.IDENT).getText();
              result = variableName.length() != 1;
          }
          else {
              final DetailAST modifiersAST = ast.findFirstToken(TokenTypes.MODIFIERS);
              final boolean isFinal = modifiersAST.findFirstToken(TokenTypes.FINAL) != null;
              result = !isFinal && ScopeUtil.isLocalVariableDef(ast);
          }
          return result;
      }
  
      /**
       * Checks if a variable is the loop's one.
       *
       * @param variableDef variable definition.
       * @return true if a variable is the loop's one.
       */
      private static boolean isForLoopVariable(DetailAST variableDef) {
          final int parentType = variableDef.getParent().getType();
          return parentType == TokenTypes.FOR_INIT
                  || parentType == TokenTypes.FOR_EACH_CLAUSE;
      }
  
  }
  