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 and bytes ** ** Bit Values ** *Byte 1 ** **
*no_caption ** *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 and bytes ** ** Bit Values ** *Byte 1 ** **
*no_caption ** *1 *1 *0 *bits 10-6 ** *Byte 2 ** **
*no_caption ** *1 *0 *bits 5-0 *
char values in the range '\u0800' to '\uFFFF' are
* represented by three bytes:
*
* ** **
*Bit values and bytes ** ** Bit Values ** *Byte 1 ** **
*no_caption ** *1 *1 *1 *0 *bits 15-12 ** *Byte 2 ** **
*no_caption ** *1 *0 *bits 11-6 ** *Byte 3 ** **
*no_caption ** *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.
* 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 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))
*
*
*
* This method is suitable for reading bytes written by the 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 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 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 some bytes from an input stream and stores them into the buffer array 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;
/**
* 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 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))
*
*
*
* This method is suitable for reading the bytes written by the 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 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 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))
*
*
*
* This method is suitable for reading the bytes written by the 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 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))
*
*
*
* If the first byte of a group matches the bit pattern 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))
*
*
*
* If the first byte of a group matches the pattern 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;
/**
* 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;
}