001    /* Checksum.java - Interface to compute a data checksum
002       Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.util.zip;
039    
040    /*
041     * Written using on-line Java Platform 1.2 API Specification, as well
042     * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998).
043     * Status:  Believed complete and correct.
044     */
045    
046    /**
047     * Interface to compute a data checksum used by checked input/output streams.
048     * A data checksum can be updated by one byte or with a byte array. After each
049     * update the value of the current checksum can be returned by calling
050     * <code>getValue</code>. The complete checksum object can also be reset
051     * so it can be used again with new data.
052     *
053     * @see CheckedInputStream
054     * @see CheckedOutputStream
055     *
056     * @author Per Bothner
057     * @author Jochen Hoenicke
058     */
059    public interface Checksum
060    {
061      /**
062       * Returns the data checksum computed so far.
063       */
064      long getValue();
065    
066      /**
067       * Resets the data checksum as if no update was ever called.
068       */
069      void reset();
070    
071      /**
072       * Adds one byte to the data checksum.
073       *
074       * @param bval the data value to add. The high byte of the int is ignored.
075       */
076      void update (int bval);
077    
078      /**
079       * Adds the byte array to the data checksum.
080       *
081       * @param buf the buffer which contains the data
082       * @param off the offset in the buffer where the data starts
083       * @param len the length of the data
084       */
085      void update (byte[] buf, int off, int len);
086    }