org.apache.hadoop.fs-Seekable

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本来要先看BufferedFSInputStream的，但是它实现了Seekable和PositionedReadable接口，就先看这两个，再看它会比较容易理解些

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 package org.apache.hadoop.fs;

 import java.io.*;

 /** Stream that permits seeking. */
 //提供按位置查找功能的接口
 public interface Seekable {
   /**
    * Seek to the given offset from the start of the file.
    * The next read() will be from that location.  Can't
    * seek past the end of the file.
    */
   void seek(long pos) throws IOException;
   //从指定文件中的位置pos，对文件流进行前向搜索。
   /**
    * Return the current offset from the start of the file
    */
   long getPos() throws IOException;
 //返回文件流中当前偏移位置。
   /**
    * Seeks a different copy of the data.  Returns true if
    * found a new source, false otherwise.
    */
   boolean seekToNewSource(long targetPos) throws IOException;
   //从targetPos位置搜索文件数据的一个不同拷贝，搜索到则返回true，否则返回false。
 }

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