DataInput interface provides
* for reading bytes from a binary stream and
* reconstructing from them data in any of
* the Java primitive types. There is also
* a
* facility for reconstructing a String
* from data in
* modified UTF-8
* format.
*
* It is generally true of all the reading
* routines in this interface that if end of
* file is reached before the desired number
* of bytes has been read, an EOFException
* (which is a kind of IOException)
* is thrown. If any byte cannot be read for
* any reason other than end of file, an IOException
* other than EOFException is
* thrown. In particular, an IOException
* may be thrown if the input stream has been
* closed.
*
*
* Implementations of the DataInput and DataOutput interfaces represent * Unicode strings in a format that is a slight modification of UTF-8. * (For information regarding the standard UTF-8 format, see section * 3.9 Unicode Encoding Forms of The Unicode Standard, Version * 4.0). * Note that in the following tables, the most significant bit appears in the * far left-hand column. *
* All characters in the range '\u0001' to
* '\u007F' are represented by a single byte:
*
*
** **
** ** Bit Values ** *Byte 1 ** **
** *0 *bits 6-0 *
* The null character '\u0000' and characters in the
* range '\u0080' to '\u07FF' are
* represented by a pair of bytes:
*
*
** **
** ** Bit Values ** *Byte 1 ** **
** *1 *1 *0 *bits 10-6 ** *Byte 2 ** **
** *1 *0 *bits 5-0 *
char values in the range '\u0800' to
* '\uFFFF' are represented by three bytes:
*
* ** **
** ** Bit Values ** *Byte 1 ** **
** *1 *1 *1 *0 *bits 15-12 ** *Byte 2 ** **
** *1 *0 *bits 11-6 ** *Byte 3 ** **
** *1 *0 *bits 5-0 *
* The differences between this format and the * standard UTF-8 format are the following: *
'\u0000' is encoded in 2-byte format
* rather than 1-byte, so that the encoded strings never have
* embedded nulls.
* b. The number of bytes
* read is equal
* to the length of b.
* * This method blocks until one of the * following conditions occurs:
*
b.length
* bytes of input data are available, in which
* case a normal return is made.
*
* EOFException
* is thrown.
*
* IOException other
* than EOFException is thrown.
*
* If b is null,
* a NullPointerException is thrown.
* If b.length is zero, then
* no bytes are read. Otherwise, the first
* byte read is stored into element b[0],
* the next one into b[1], and
* so on.
* If an exception is thrown from
* this method, then it may be that some but
* not all bytes of b have been
* updated with data from the input stream.
*
* @param b the buffer into which the data is read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
void readFully(byte b[]) throws IOException;
/**
*
* Reads len
* bytes from
* an input stream.
*
* This method * blocks until one of the following conditions * occurs:
*
len bytes
* of input data are available, in which case
* a normal return is made.
*
* EOFException
* is thrown.
*
* IOException other
* than EOFException is thrown.
*
* If b is null,
* a NullPointerException is thrown.
* If off is negative, or len
* is negative, or off+len is
* greater than the length of the array b,
* then an IndexOutOfBoundsException
* is thrown.
* If len is zero,
* then no bytes are read. Otherwise, the first
* byte read is stored into element b[off],
* the next one into b[off+1],
* and so on. The number of bytes read is,
* at most, equal to len.
*
* @param b the buffer into which the data is read.
* @param off an int specifying the offset into the data.
* @param len an int specifying the number of bytes to read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
void readFully(byte b[], int off, int len) throws IOException;
/**
* Makes an attempt to skip over
* n bytes
* of data from the input
* stream, discarding the skipped bytes. However,
* it may skip
* over some smaller number of
* bytes, possibly zero. This may result from
* any of a
* number of conditions; reaching
* end of file before n bytes
* have been skipped is
* only one possibility.
* This method never throws an EOFException.
* The actual
* number of bytes skipped is returned.
*
* @param n the number of bytes to be skipped.
* @return the number of bytes actually skipped.
* @exception IOException if an I/O error occurs.
*/
int skipBytes(int n) throws IOException;
/**
* Reads one input byte and returns
* true if that byte is nonzero,
* false if that byte is zero.
* This method is suitable for reading
* the byte written by the writeBoolean
* method of interface DataOutput.
*
* @return the boolean value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
boolean readBoolean() throws IOException;
/**
* Reads and returns one input byte.
* The byte is treated as a signed value in
* the range -128 through 127,
* inclusive.
* This method is suitable for
* reading the byte written by the writeByte
* method of interface DataOutput.
*
* @return the 8-bit value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
byte readByte() throws IOException;
/**
* Reads one input byte, zero-extends
* it to type int, and returns
* the result, which is therefore in the range
* 0
* through 255.
* This method is suitable for reading
* the byte written by the writeByte
* method of interface DataOutput
* if the argument to writeByte
* was intended to be a value in the range
* 0 through 255.
*
* @return the unsigned 8-bit value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
int readUnsignedByte() throws IOException;
/**
* Reads two input bytes and returns
* a short value. Let a
* be the first byte read and b
* be the second byte. The value
* returned
* is:
*
(short)((a << 8) | (b & 0xff))
* writeShort method of
* interface DataOutput.
*
* @return the 16-bit value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
short readShort() throws IOException;
/**
* Reads two input bytes and returns
* an int value in the range 0
* through 65535. Let a
* be the first byte read and
* b
* be the second byte. The value returned is:
* (((a & 0xff) << 8) | (b & 0xff))
* writeShort method
* of interface DataOutput if
* the argument to writeShort
* was intended to be a value in the range
* 0 through 65535.
*
* @return the unsigned 16-bit value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
int readUnsignedShort() throws IOException;
/**
* Reads two input bytes and returns a char value.
* Let a
* be the first byte read and b
* be the second byte. The value
* returned is:
* (char)((a << 8) | (b & 0xff))
* writeChar method of interface
* DataOutput.
*
* @return the char value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
char readChar() throws IOException;
/**
* Reads four input bytes and returns an
* int value. Let a-d
* be the first through fourth bytes read. The value returned is:
*
*
* (((a & 0xff) << 24) | ((b & 0xff) << 16) |
* ((c & 0xff) << 8) | (d & 0xff))
*
* This method is suitable
* for reading bytes written by the writeInt
* method of interface DataOutput.
*
* @return the int value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
int readInt() throws IOException;
/**
* Reads eight input bytes and returns
* a long value. Let a-h
* be the first through eighth bytes read.
* The value returned is:
*
* (((long)(a & 0xff) << 56) |
* ((long)(b & 0xff) << 48) |
* ((long)(c & 0xff) << 40) |
* ((long)(d & 0xff) << 32) |
* ((long)(e & 0xff) << 24) |
* ((long)(f & 0xff) << 16) |
* ((long)(g & 0xff) << 8) |
* ((long)(h & 0xff)))
*
*
* This method is suitable
* for reading bytes written by the writeLong
* method of interface DataOutput.
*
* @return the long value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
long readLong() throws IOException;
/**
* Reads four input bytes and returns
* a float value. It does this
* by first constructing an int
* value in exactly the manner
* of the readInt
* method, then converting this int
* value to a float in
* exactly the manner of the method Float.intBitsToFloat.
* This method is suitable for reading
* bytes written by the writeFloat
* method of interface DataOutput.
*
* @return the float value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
float readFloat() throws IOException;
/**
* Reads eight input bytes and returns
* a double value. It does this
* by first constructing a long
* value in exactly the manner
* of the readlong
* method, then converting this long
* value to a double in exactly
* the manner of the method Double.longBitsToDouble.
* This method is suitable for reading
* bytes written by the writeDouble
* method of interface DataOutput.
*
* @return the double value read.
* @exception EOFException if this stream reaches the end before reading
* all the bytes.
* @exception IOException if an I/O error occurs.
*/
double readDouble() throws IOException;
/**
* Reads the next line of text from the input stream.
* It reads successive bytes, converting
* each byte separately into a character,
* until it encounters a line terminator or
* end of
* file; the characters read are then
* returned as a String. Note
* that because this
* method processes bytes,
* it does not support input of the full Unicode
* character set.
*
* If end of file is encountered
* before even one byte can be read, then null
* is returned. Otherwise, each byte that is
* read is converted to type char
* by zero-extension. If the character '\n'
* is encountered, it is discarded and reading
* ceases. If the character '\r'
* is encountered, it is discarded and, if
* the following byte converts to the
* character '\n', then that is
* discarded also; reading then ceases. If
* end of file is encountered before either
* of the characters '\n' and
* '\r' is encountered, reading
* ceases. Once reading has ceased, a String
* is returned that contains all the characters
* read and not discarded, taken in order.
* Note that every character in this string
* will have a value less than \u0100,
* that is, (char)256.
*
* @return the next line of text from the input stream,
* or null if the end of file is
* encountered before a byte can be read.
* @exception IOException if an I/O error occurs.
*/
String readLine() throws IOException;
/**
* Reads in a string that has been encoded using a
* modified UTF-8
* format.
* The general contract of readUTF
* is that it reads a representation of a Unicode
* character string encoded in modified
* UTF-8 format; this string of characters
* is then returned as a String.
*
* First, two bytes are read and used to
* construct an unsigned 16-bit integer in
* exactly the manner of the readUnsignedShort
* method . This integer value is called the
* UTF length and specifies the number
* of additional bytes to be read. These bytes
* are then converted to characters by considering
* them in groups. The length of each group
* is computed from the value of the first
* byte of the group. The byte following a
* group, if any, is the first byte of the
* next group.
*
* If the first byte of a group
* matches the bit pattern 0xxxxxxx
* (where x means "may be 0
* or 1"), then the group consists
* of just that byte. The byte is zero-extended
* to form a character.
*
* If the first byte
* of a group matches the bit pattern 110xxxxx,
* then the group consists of that byte a
* and a second byte b. If there
* is no byte b (because byte
* a was the last of the bytes
* to be read), or if byte b does
* not match the bit pattern 10xxxxxx,
* then a UTFDataFormatException
* is thrown. Otherwise, the group is converted
* to the character:
*
(char)(((a& 0x1F) << 6) | (b & 0x3F))
* 1110xxxx,
* then the group consists of that byte a
* and two more bytes b and c.
* If there is no byte c (because
* byte a was one of the last
* two of the bytes to be read), or either
* byte b or byte c
* does not match the bit pattern 10xxxxxx,
* then a UTFDataFormatException
* is thrown. Otherwise, the group is converted
* to the character:*
* (char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))
* 1111xxxx or the pattern
* 10xxxxxx, then a UTFDataFormatException
* is thrown.
*
* If end of file is encountered
* at any time during this entire process,
* then an EOFException is thrown.
*
* After every group has been converted to
* a character by this process, the characters
* are gathered, in the same order in which
* their corresponding groups were read from
* the input stream, to form a String,
* which is returned.
*
* The writeUTF
* method of interface DataOutput
* may be used to write data that is suitable
* for reading by this method.
* @return a Unicode string.
* @exception EOFException if this stream reaches the end
* before reading all the bytes.
* @exception IOException if an I/O error occurs.
* @exception UTFDataFormatException if the bytes do not represent a
* valid modified UTF-8 encoding of a string.
*/
String readUTF() throws IOException;
}