- All Known Subinterfaces:
ImageInputStream,ImageOutputStream,ObjectInput
- All Known Implementing Classes:
DataInputStream,FileCacheImageInputStream,FileCacheImageOutputStream,FileImageInputStream,FileImageOutputStream,ImageInputStreamImpl,ImageOutputStreamImpl,MemoryCacheImageInputStream,MemoryCacheImageOutputStream,ObjectInputStream,RandomAccessFile
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.
Modified UTF-8
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)
- Characters in the range
'\u0001'to'\u007F'are represented by a single byte. - The null character
'\u0000'and characters in the range'\u0080'to'\u07FF'are represented by a pair of bytes. - Characters in the range
'\u0800'to'\uFFFF'are represented by three bytes.
| Value | Byte | Bit Values | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | ||
\u0001 to \u007F |
1 | 0 | bits 6-0 | ||||||
\u0000,\u0080 to \u07FF |
1 | 1 | 1 | 0 | bits 10-6 | ||||
| 2 | 1 | 0 | bits 5-0 | ||||||
\u0800 to \uFFFF |
1 | 1 | 1 | 1 | 0 | bits 15-12 | |||
| 2 | 1 | 0 | bits 11-6 | ||||||
| 3 | 1 | 0 | bits 5-0 | ||||||
The differences between this format and the standard UTF-8 format are the following:
- The null byte
'\u0000'is encoded in 2-byte format rather than 1-byte, so that the encoded strings never have embedded nulls. - Only the 1-byte, 2-byte, and 3-byte formats are used.
- Supplementary characters are represented in the form of surrogate pairs.
- Since:
- 1.0
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptionbooleanReads one input byte and returnstrueif that byte is nonzero,falseif that byte is zero.bytereadByte()Reads and returns one input byte.charreadChar()Reads two input bytes and returns acharvalue.doubleReads eight input bytes and returns adoublevalue.floatReads four input bytes and returns afloatvalue.voidreadFully(byte[] b) Reads some bytes from an input stream and stores them into the buffer arrayb.voidreadFully(byte[] b, int off, int len) Readslenbytes from an input stream.intreadInt()Reads four input bytes and returns anintvalue.readLine()Reads the next line of text from the input stream.longreadLong()Reads eight input bytes and returns alongvalue.shortReads two input bytes and returns ashortvalue.intReads one input byte, zero-extends it to typeint, and returns the result, which is therefore in the range0through255.intReads two input bytes and returns anintvalue in the range0through65535.readUTF()Reads in a string that has been encoded using a modified UTF-8 format.intskipBytes(int n) Makes an attempt to skip overnbytes of data from the input stream, discarding the skipped bytes.
-
Method Details
-
readFully
Reads some bytes from an input stream and stores them into the buffer arrayb. The number of bytes read is equal to the length ofb.This method blocks until one of the following conditions occurs:
b.lengthbytes of input data are available, in which case a normal return is made.- End of
file is detected, in which case an
EOFExceptionis thrown. - An I/O error occurs, in
which case an
IOExceptionother thanEOFExceptionis thrown.
If
bisnull, aNullPointerExceptionis thrown. Ifb.lengthis zero, then no bytes are read. Otherwise, the first byte read is stored into elementb[0], the next one intob[1], and so on. If an exception is thrown from this method, then it may be that some but not all bytes ofbhave been updated with data from the input stream.- Parameters:
b- the buffer into which the data is read.- Throws:
NullPointerException- ifbisnull.EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readFully
Readslenbytes from an input stream.This method blocks until one of the following conditions occurs:
lenbytes of input data are available, in which case a normal return is made.- End of file
is detected, in which case an
EOFExceptionis thrown. - An I/O error occurs, in
which case an
IOExceptionother thanEOFExceptionis thrown.
If
bisnull, aNullPointerExceptionis thrown. Ifoffis negative, orlenis negative, oroff+lenis greater than the length of the arrayb, then anIndexOutOfBoundsExceptionis thrown. Iflenis zero, then no bytes are read. Otherwise, the first byte read is stored into elementb[off], the next one intob[off+1], and so on. The number of bytes read is, at most, equal tolen.- Parameters:
b- the buffer into which the data is read.off- an int specifying the offset in the data arrayb.len- an int specifying the number of bytes to read.- Throws:
NullPointerException- ifbisnull.IndexOutOfBoundsException- ifoffis negative,lenis negative, orlenis greater thanb.length - off.EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
skipBytes
Makes an attempt to skip overnbytes 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 beforenbytes have been skipped is only one possibility. This method never throws anEOFException. The actual number of bytes skipped is returned.- Parameters:
n- the number of bytes to be skipped.- Returns:
- the number of bytes actually skipped.
- Throws:
IOException- if an I/O error occurs.
-
readBoolean
Reads one input byte and returnstrueif that byte is nonzero,falseif that byte is zero. This method is suitable for reading the byte written by thewriteBooleanmethod of interfaceDataOutput.- Returns:
- the
booleanvalue read. - Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readByte
Reads and returns one input byte. The byte is treated as a signed value in the range-128through127, inclusive. This method is suitable for reading the byte written by thewriteBytemethod of interfaceDataOutput.- Returns:
- the 8-bit value read.
- Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readUnsignedByte
Reads one input byte, zero-extends it to typeint, and returns the result, which is therefore in the range0through255. This method is suitable for reading the byte written by thewriteBytemethod of interfaceDataOutputif the argument towriteBytewas intended to be a value in the range0through255.- Returns:
- the unsigned 8-bit value read.
- Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readShort
Reads two input bytes and returns ashortvalue. Letabe the first byte read andbbe the second byte. The value returned is:
This method is suitable for reading the bytes written by the(short)((a << 8) | (b & 0xff))writeShortmethod of interfaceDataOutput.- Returns:
- the 16-bit value read.
- Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readUnsignedShort
Reads two input bytes and returns anintvalue in the range0through65535. Letabe the first byte read andbbe the second byte. The value returned is:
This method is suitable for reading the bytes written by the(((a & 0xff) << 8) | (b & 0xff))writeShortmethod of interfaceDataOutputif the argument towriteShortwas intended to be a value in the range0through65535.- Returns:
- the unsigned 16-bit value read.
- Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readChar
Reads two input bytes and returns acharvalue. Letabe the first byte read andbbe the second byte. The value returned is:
This method is suitable for reading bytes written by the(char)((a << 8) | (b & 0xff))writeCharmethod of interfaceDataOutput.- Returns:
- the
charvalue read. - Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readInt
Reads four input bytes and returns anintvalue. Leta-dbe the first through fourth bytes read. The value returned is:
This method is suitable for reading bytes written by the(((a & 0xff) << 24) | ((b & 0xff) << 16) | ((c & 0xff) << 8) | (d & 0xff))writeIntmethod of interfaceDataOutput.- Returns:
- the
intvalue read. - Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readLong
Reads eight input bytes and returns alongvalue. Leta-hbe 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
writeLongmethod of interfaceDataOutput.- Returns:
- the
longvalue read. - Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readFloat
Reads four input bytes and returns afloatvalue. It does this by first constructing anintvalue in exactly the manner of thereadIntmethod, then converting thisintvalue to afloatin exactly the manner of the methodFloat.intBitsToFloat. This method is suitable for reading bytes written by thewriteFloatmethod of interfaceDataOutput.- Returns:
- the
floatvalue read. - Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readDouble
Reads eight input bytes and returns adoublevalue. It does this by first constructing alongvalue in exactly the manner of thereadLongmethod, then converting thislongvalue to adoublein exactly the manner of the methodDouble.longBitsToDouble. This method is suitable for reading bytes written by thewriteDoublemethod of interfaceDataOutput.- Returns:
- the
doublevalue read. - Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.
-
readLine
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 aString. 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
nullis returned. Otherwise, each byte that is read is converted to typecharby 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, aStringis 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.- Returns:
- the next line of text from the input stream,
or
nullif the end of file is encountered before a byte can be read. - Throws:
IOException- if an I/O error occurs.
-
readUTF
Reads in a string that has been encoded using a modified UTF-8 format. The general contract ofreadUTFis that it reads a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as aString.First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the
readUnsignedShortmethod . 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(wherexmeans "may be0or1"), 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 byteaand a second byteb. If there is no byteb(because byteawas the last of the bytes to be read), or if bytebdoes not match the bit pattern10xxxxxx, then aUTFDataFormatExceptionis thrown. Otherwise, the group is converted to the character:
If the first byte of a group matches the bit pattern(char)(((a & 0x1F) << 6) | (b & 0x3F))1110xxxx, then the group consists of that byteaand two more bytesbandc. If there is no bytec(because byteawas one of the last two of the bytes to be read), or either bytebor bytecdoes not match the bit pattern10xxxxxx, then aUTFDataFormatExceptionis thrown. Otherwise, the group is converted to the character:
If the first byte of a group matches the pattern(char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))1111xxxxor the pattern10xxxxxx, then aUTFDataFormatExceptionis thrown.If end of file is encountered at any time during this entire process, then an
EOFExceptionis 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
writeUTFmethod of interfaceDataOutputmay be used to write data that is suitable for reading by this method.- Returns:
- a Unicode string.
- Throws:
EOFException- if this stream reaches the end before reading all the bytes.IOException- if an I/O error occurs.UTFDataFormatException- if the bytes do not represent a valid modified UTF-8 encoding of a string.
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