gt:         mParameterNames = mParameterNamesStack.pop();
context: ////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code for adherence to a set of rules.
  // Copyright (C) 2001-2010  Oliver Burn
  //
  // 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.coding;
  
  import com.google.common.collect.Sets;
  import com.puppycrawl.tools.checkstyle.api.Check;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.FastStack;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import java.util.Set;
  
  /**
   * <p>
   * Disallow assignment of parameters.
   * </p>
   * <p>
   * Rationale:
   * Parameter assignment is often considered poor
   * programming practice. Forcing developers to declare
   * parameters as final is often onerous. Having a check
   * ensure that parameters are never assigned would give
   * the best of both worlds.
   * </p>
   * @author <a href="mailto:simon@redhillconsulting.com.au">Simon Harris</a>
   */
  public final class ParameterAssignmentCheck extends Check
  {
      /** Stack of methods' parameters. */
      private final FastStack<Set<String>> mParameterNamesStack =
          FastStack.newInstance();
      /** Current set of perameters. */
      private Set<String> mParameterNames;
  
      @Override
      public int[] getDefaultTokens()
      {
          return new int[] {
              TokenTypes.CTOR_DEF,
              TokenTypes.METHOD_DEF,
              TokenTypes.ASSIGN,
              TokenTypes.PLUS_ASSIGN,
              TokenTypes.MINUS_ASSIGN,
              TokenTypes.STAR_ASSIGN,
              TokenTypes.DIV_ASSIGN,
              TokenTypes.MOD_ASSIGN,
              TokenTypes.SR_ASSIGN,
              TokenTypes.BSR_ASSIGN,
              TokenTypes.SL_ASSIGN,
              TokenTypes.BAND_ASSIGN,
              TokenTypes.BXOR_ASSIGN,
              TokenTypes.BOR_ASSIGN,
              TokenTypes.INC,
              TokenTypes.POST_INC,
              TokenTypes.DEC,
              TokenTypes.POST_DEC,
          };
      }
  
      @Override
      public int[] getRequiredTokens()
      {
          return getDefaultTokens();
      }
  
      @Override
      public void beginTree(DetailAST aRootAST)
      {
          // clear data
          mParameterNamesStack.clear();
          mParameterNames = null;
      }
  
      @Override
      public void visitToken(DetailAST aAST)
      {
          switch (aAST.getType()) {
          case TokenTypes.CTOR_DEF:
          case TokenTypes.METHOD_DEF:
              visitMethodDef(aAST);
              break;
          case TokenTypes.ASSIGN:
          case TokenTypes.PLUS_ASSIGN:
          case TokenTypes.MINUS_ASSIGN:
          case TokenTypes.STAR_ASSIGN:
          case TokenTypes.DIV_ASSIGN:
          case TokenTypes.MOD_ASSIGN:
          case TokenTypes.SR_ASSIGN:
          case TokenTypes.BSR_ASSIGN:
          case TokenTypes.SL_ASSIGN:
          case TokenTypes.BAND_ASSIGN:
          case TokenTypes.BXOR_ASSIGN:
          case TokenTypes.BOR_ASSIGN:
              visitAssign(aAST);
              break;
          case TokenTypes.INC:
          case TokenTypes.POST_INC:
          case TokenTypes.DEC:
          case TokenTypes.POST_DEC:
              visitIncDec(aAST);
              break;
          default:
              throw new IllegalStateException(aAST.toString());
          }
      }
  
      @Override
      public void leaveToken(DetailAST aAST)
      {
          switch (aAST.getType()) {
          case TokenTypes.CTOR_DEF:
          case TokenTypes.METHOD_DEF:
              leaveMethodDef();
              break;
          case TokenTypes.ASSIGN:
          case TokenTypes.PLUS_ASSIGN:
          case TokenTypes.MINUS_ASSIGN:
          case TokenTypes.STAR_ASSIGN:
          case TokenTypes.DIV_ASSIGN:
          case TokenTypes.MOD_ASSIGN:
          case TokenTypes.SR_ASSIGN:
          case TokenTypes.BSR_ASSIGN:
          case TokenTypes.SL_ASSIGN:
          case TokenTypes.BAND_ASSIGN:
          case TokenTypes.BXOR_ASSIGN:
          case TokenTypes.BOR_ASSIGN:
          case TokenTypes.INC:
          case TokenTypes.POST_INC:
          case TokenTypes.DEC:
          case TokenTypes.POST_DEC:
              // Do nothing
              break;
          default:
              throw new IllegalStateException(aAST.toString());
          }
      }
  
      /**
       * Ckecks if this is assignments of parameter.
       * @param aAST assignment to check.
       */
      private void visitAssign(DetailAST aAST)
      {
          checkIdent(aAST);
      }
  
      /**
       * Checks if this is increment/decrement of parameter.
       * @param aAST dec/inc to check.
       */
      private void visitIncDec(DetailAST aAST)
      {
          checkIdent(aAST);
      }
  
      /**
       * Check if ident is parameter.
       * @param aAST ident to check.
       */
      private void checkIdent(DetailAST aAST)
      {
          if ((mParameterNames != null) && !mParameterNames.isEmpty()) {
              final DetailAST identAST = aAST.getFirstChild();
  
              if ((identAST != null)
                  && (identAST.getType() == TokenTypes.IDENT)
                  && mParameterNames.contains(identAST.getText()))
              {
                  log(aAST.getLineNo(), aAST.getColumnNo(),
                      "parameter.assignment", identAST.getText());
              }
          }
      }
  
      /**
       * Creates new set of parameters and store old one in stack.
       * @param aAST a method to process.
       */
      private void visitMethodDef(DetailAST aAST)
      {
          mParameterNamesStack.push(mParameterNames);
          mParameterNames = Sets.newHashSet();
  
          visitMethodParameters(aAST.findFirstToken(TokenTypes.PARAMETERS));
      }
  
      /** Restores old set of parameters. */
      private void leaveMethodDef()
      {
  