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   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code 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 General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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   */
  
  package java.sql;
  
  /**
   * Interface for JDBC classes which provide the ability to retrieve the delegate instance when the instance
   * in question is in fact a proxy class.
   * <p>
   * The wrapper pattern is employed by many JDBC driver implementations to provide extensions beyond
   * the traditional JDBC API that are specific to a data source. Developers may wish to gain access to
   * these resources that are wrapped (the delegates) as  proxy class instances representing the
   * the actual resources. This interface describes a standard mechanism to access
   * these wrapped resources
   * represented by their proxy, to permit direct access to the resource delegates.
   *
   * @since 1.6
   */
  
  public interface Wrapper {
  
      /**
       * Returns an object that implements the given interface to allow access to
       * non-standard methods, or standard methods not exposed by the proxy.
       *
       * If the receiver implements the interface then the result is the receiver
       * or a proxy for the receiver. If the receiver is a wrapper
       * and the wrapped object implements the interface then the result is the
       * wrapped object or a proxy for the wrapped object. Otherwise return the
       * the result of calling <code>unwrap</code> recursively on the wrapped object
       * or a proxy for that result. If the receiver is not a
       * wrapper and does not implement the interface, then an <code>SQLException</code> is thrown.
       *
       * @param iface A Class defining an interface that the result must implement.
       * @return an object that implements the interface. May be a proxy for the actual implementing object.
       * @throws SQLException If no object found that implements the interface
       * @since 1.6
       */
          <T> T unwrap(Class<T> iface) throws SQLException;
  
      /**
       * Returns true if this either implements the interface argument or is directly or indirectly a wrapper
       * for an object that does. Returns false otherwise. If this implements the interface then return true,
       * else if this is a wrapper then return the result of recursively calling <code>isWrapperFor</code> on the wrapped
       * object. If this does not implement the interface and is not a wrapper, return false.
       * This method should be implemented as a low-cost operation compared to <code>unwrap</code> so that
       * callers can use this method to avoid expensive <code>unwrap</code> calls that may fail. If this method
       * returns true then calling <code>unwrap</code> with the same argument should succeed.
       *
       * @param iface a Class defining an interface.
       * @return true if this implements the interface or directly or indirectly wraps an object that does.
       * @throws SQLException  if an error occurs while determining whether this is a wrapper
       * for an object with the given interface.
       * @since 1.6
       */
      boolean isWrapperFor(Class<?> iface) throws SQLException;
  
  }
  