public Object clone() 
{
    IndexInput clone = null;
    try {
      clone = (IndexInput)super.clone();
    } catch (CloneNotSupportedException e) {}
    clone.bytes = null;
    clone.chars = null;
    return clone;
}

Returns a clone of this stream.

Clones of a stream access the same data, and are positioned at the same point as the stream they were cloned from.

Expert: Subclasses must ensure that clones may be positioned at different points in the input from each other and from the stream they were cloned from.

 abstract public  void close() throws IOException
Closes the stream to further operations.

 abstract public long getFilePointer()
Returns the current position in this file, where the next read will
occur.

 abstract public long length()
The number of bytes in the file.

 abstract public byte readByte() throws IOException
Reads and returns a single byte.

 abstract public  void readBytes(byte[] b,
    int offset,
    int len) throws IOException
Reads a specified number of bytes into an array at the specified offset.

 public  void readBytes(byte[] b,
    int offset,
    int len,
    boolean useBuffer) throws IOException 
{
    // Default to ignoring useBuffer entirely
    readBytes(b, offset, len);
}

Reads a specified number of bytes into an array at the specified offset with control over whether the read should be buffered (callers who have their own buffer should pass in "false" for useBuffer). Currently only BufferedIndexInput respects this parameter.

 public  void readChars(char[] buffer,
    int start,
    int length) throws IOException 
{
    final int end = start + length;
    for (int i = start; i <  end; i++) {
      byte b = readByte();
      if ((b & 0x80) == 0)
	buffer[i] = (char)(b & 0x7F);
      else if ((b & 0xE0) != 0xE0) {
	buffer[i] = (char)(((b & 0x1F) < <  6)
		 | (readByte() & 0x3F));
      } else
	buffer[i] = (char)(((b & 0x0F) < <  12)
		| ((readByte() & 0x3F) < <  6)
	        |  (readByte() & 0x3F));
    }
}

Reads Lucene's old "modified UTF-8" encoded characters into an array.

 public int readInt() throws IOException 
{
    return ((readByte() & 0xFF) < <  24) | ((readByte() & 0xFF) < <  16)
         | ((readByte() & 0xFF) < <   8) |  (readByte() & 0xFF);
}

Reads four bytes and returns an int.

 public long readLong() throws IOException 
{
    return (((long)readInt()) < <  32) | (readInt() & 0xFFFFFFFFL);
}

Reads eight bytes and returns a long.

 public String readString() throws IOException 
{
    if (preUTF8Strings)
      return readModifiedUTF8String();
    int length = readVInt();
    if (bytes == null || length  > bytes.length)
      bytes = new byte[(int) (length*1.25)];
    readBytes(bytes, 0, length);
    return new String(bytes, 0, length, "UTF-8");
}

Reads a string.

 public Map<String, String> readStringStringMap() throws IOException 
{
    final Map< String,String > map = new HashMap< String,String >();
    final int count = readInt();
    for(int i=0;i< count;i++) {
      final String key = readString();
      final String val = readString();
      map.put(key, val);
    }
    return map;
}

 public int readVInt() throws IOException 
{
    byte b = readByte();
    int i = b & 0x7F;
    for (int shift = 7; (b & 0x80) != 0; shift += 7) {
      b = readByte();
      i |= (b & 0x7F) < <  shift;
    }
    return i;
}

Reads an int stored in variable-length format. Reads between one and five bytes. Smaller values take fewer bytes. Negative numbers are not supported.

 public long readVLong() throws IOException 
{
    byte b = readByte();
    long i = b & 0x7F;
    for (int shift = 7; (b & 0x80) != 0; shift += 7) {
      b = readByte();
      i |= (b & 0x7FL) < <  shift;
    }
    return i;
}

Reads a long stored in variable-length format. Reads between one and nine bytes. Smaller values take fewer bytes. Negative numbers are not supported.

 abstract public  void seek(long pos) throws IOException
Sets current position in this file, where the next read will occur.

 public  void setModifiedUTF8StringsMode() 
{
    preUTF8Strings = true;
}

Call this if readString should read characters stored in the old modified UTF8 format (length in java chars and java's modified UTF8 encoding). This is used for indices written pre-2.4 See LUCENE-510 for details.

 public  void skipChars(int length) throws IOException 
{
    for (int i = 0; i <  length; i++) {
      byte b = readByte();
      if ((b & 0x80) == 0){
        //do nothing, we only need one byte
      }
      else if ((b & 0xE0) != 0xE0) {
        readByte();//read an additional byte
      } else{      
        //read two additional bytes.
        readByte();
        readByte();
      }
    }
}

Expert Similar to #readChars(char[], int, int) but does not do any conversion operations on the bytes it is reading in. It still has to invoke #readByte() just as #readChars(char[], int, int) does, but it does not need a buffer to store anything and it does not have to do any of the bitwise operations, since we don't actually care what is in the byte except to determine how many more bytes to read