content: /*
   * This library is part of OpenCms -
   * the Open Source Content Management System
   *
   * Copyright (c) Alkacon Software GmbH & Co. KG (https://www.alkacon.com)
   *
   * 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.
   *
   * For further information about Alkacon Software, please see the
   * company website: https://www.alkacon.com
   *
   * For further information about OpenCms, please see the
   * project website: https://www.opencms.org
   *
   * 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 org.opencms.util;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Thread local stack.
   *
   * @param <T> the type for the stack elements
   */
  public class CmsThreadLocalStack<T> {
  
      /** The internal ThreadLocal storing the list. */
      private ThreadLocal<List<T>> m_stackVar = ThreadLocal.withInitial(() -> new ArrayList<T>());
  
      /**
       * Removes and returns the last element pushed onto the stack.
       *
       * @return the last element pushed onto the stack
       */
      public T pop() {
  
          return getStack().remove(getStack().size() - 1);
      }
  
      /**
       * Pushes a new element onto the stack.
       *
       * @param data the element to push on the stack
       */
      public void push(T data) {
  
          getStack().add(data);
      }
  
      /**
       * Returns the current stack size.
       *
       * @return the current stack size
       */
      public int size() {
  
          return getStack().size();
      }
  
      /**
       * Returns the current top of the stack, without removing it.
       * <p>
       * If the stack is empty, null is returned.
       *
       * @return the current top of the stack
       */
      public T top() {
  
          if (getStack().size() == 0) {
              return null;
          } else {
              return getStack().get(getStack().size() - 1);
          }
      }
  
      /**
       * Gets the current list stored in the ThreadLocal.
       *
       * @return the current list stored in the ThreadLocal
       */
      private List<T> getStack() {
  
          return m_stackVar.get();
      }
  
  }
  