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java.lang.Objectjava.io.InputStream
java.io.FilterInputStream
java.io.DataInputStream
public class DataInputStream
This subclass of FilteredInputStream
implements the
DataInput
interface that provides method for reading primitive
Java data types from a stream.
DataInput
Field Summary |
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Fields inherited from class java.io.FilterInputStream |
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in |
Constructor Summary | |
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DataInputStream(InputStream in)
This constructor initializes a new DataInputStream
to read from the specified subordinate stream. |
Method Summary | |
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int |
read(byte[] b)
This method reads bytes from the underlying stream into the specified byte array buffer. |
int |
read(byte[] b,
int off,
int len)
This method reads bytes from the underlying stream into the specified byte array buffer. |
boolean |
readBoolean()
This method reads a Java boolean value from an input stream. |
byte |
readByte()
This method reads a Java byte value from an input stream. |
char |
readChar()
This method reads a Java char value from an input stream. |
double |
readDouble()
This method reads a Java double value from an input stream. |
float |
readFloat()
This method reads a Java float value from an input stream. |
void |
readFully(byte[] b)
This method reads raw bytes into the passed array until the array is full. |
void |
readFully(byte[] buf,
int offset,
int len)
This method reads raw bytes into the passed array buf
starting
offset bytes into the buffer. |
int |
readInt()
This method reads a Java int value from an input stream
It operates by reading four bytes from the stream and converting them to
a single Java int . |
String |
readLine()
Deprecated. |
long |
readLong()
This method reads a Java long value from an input stream
It operates by reading eight bytes from the stream and converting them to
a single Java long . |
short |
readShort()
This method reads a signed 16-bit value into a Java in from the stream. |
int |
readUnsignedByte()
This method reads 8 unsigned bits into a Java int
value from the stream. |
int |
readUnsignedShort()
This method reads 16 unsigned bits into a Java int value from the stream. |
String |
readUTF()
This method reads a String from an input stream that
is encoded in a modified UTF-8 format. |
static String |
readUTF(DataInput in)
This method reads a String encoded in UTF-8 format from the specified DataInput source. |
int |
skipBytes(int n)
This method attempts to skip and discard the specified number of bytes in the input stream. |
Methods inherited from class java.io.FilterInputStream |
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available, close, mark, markSupported, read, reset, skip |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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public DataInputStream(InputStream in)
DataInputStream
to read from the specified subordinate stream.
in
- The subordinate InputStream
to read fromMethod Detail |
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public final int read(byte[] b) throws IOException
read
in class FilterInputStream
b
- The buffer into which bytes will be read.
IOException
- If an error occurs.public final int read(byte[] b, int off, int len) throws IOException
len
bytes and
will start storing them at position off
into the buffer.
This method can return a short count if there is insufficient data
remaining to be read to complete the desired read length.
read
in class FilterInputStream
b
- The buffer into which bytes will be read.off
- The offset into the buffer to start storing bytes.len
- The requested number of bytes to read.
IOException
- If an error occurs.public final boolean readBoolean() throws IOException
false
. If the byte is non-zero, then
the value returned is true
.
This method can read a boolean
written by an object
implementing the writeBoolean()
method in the
DataOutput
interface.
readBoolean
in interface DataInput
boolean
value read
EOFException
- If end of file is reached before reading
the boolean
IOException
- If any other error occursDataOutput.writeBoolean(boolean)
public final byte readByte() throws IOException
This method can read a byte
written by an object
implementing the writeByte()
method in the
DataOutput
interface.
readByte
in interface DataInput
byte
value read
EOFException
- If end of file is reached before reading the byte
IOException
- If any other error occursDataOutput.writeByte(int)
public final char readChar() throws IOException
char
value from an input stream.
It operates by reading two bytes from the stream and converting them to
a single 16-bit Java char
. The two bytes are stored most
significant byte first (i.e., "big endian") regardless of the native
host byte ordering.
As an example, if byte1
and byte2
represent the first and second byte read from the stream
respectively, they will be transformed to a char
in
the following manner:
(char)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)
This method can read a char
written by an object
implementing the writeChar()
method in the
DataOutput
interface.
readChar
in interface DataInput
char
value read
EOFException
- If end of file is reached before reading the char
IOException
- If any other error occursDataOutput.writeChar(int)
public final double readDouble() throws IOException
long
value from the stream by calling the
readLong()
method in this interface, then converts
that long
to a double
using the
longBitsToDouble
method in the class
java.lang.Double
This method can read a double
written by an object
implementing the writeDouble()
method in the
DataOutput
interface.
readDouble
in interface DataInput
double
value read
EOFException
- If end of file is reached before reading
the double
IOException
- If any other error occursDataOutput.writeDouble(double)
,
Double.longBitsToDouble(long)
public final float readFloat() throws IOException
int
value from the
stream by calling the readInt()
method in this
interface, then converts that int
to a
float
using the intBitsToFloat
method
in the class java.lang.Float
This method can read a float
written by an object
implementing the writeFloat()
method in the
DataOutput
interface.
readFloat
in interface DataInput
float
value read
EOFException
- If end of file is reached before reading the float
IOException
- If any other error occursDataOutput.writeFloat(float)
,
Float.intBitsToFloat(int)
public final void readFully(byte[] b) throws IOException
readFully
in interface DataInput
b
- The buffer into which to read the data
EOFException
- If end of file is reached before filling the
buffer
IOException
- If any other error occurspublic final void readFully(byte[] buf, int offset, int len) throws IOException
buf
starting
offset
bytes into the buffer. The number of bytes read
will be
exactly len
. Note that this method blocks until the data is
available and throws an exception if there is not enough data left in
the stream to read len
bytes. Note also that zero length
buffers are permitted. In this case, the method will return immediately
without reading any bytes from the stream.
readFully
in interface DataInput
buf
- The buffer into which to read the dataoffset
- The offset into the buffer to start storing datalen
- The number of bytes to read into the buffer
EOFException
- If end of file is reached before filling the
buffer
IOException
- If any other error occurspublic final int readInt() throws IOException
int
value from an input stream
It operates by reading four bytes from the stream and converting them to
a single Java int
. The bytes are stored most
significant byte first (i.e., "big endian") regardless of the native
host byte ordering.
As an example, if byte1
through byte4
represent
the first four bytes read from the stream, they will be
transformed to an int
in the following manner:
(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) +
((byte3 & 0xFF)<< 8) + (byte4 & 0xFF)))
The value returned is in the range of -2147483648 to 2147483647.
This method can read an int
written by an object
implementing the writeInt()
method in the
DataOutput
interface.
readInt
in interface DataInput
int
value read
EOFException
- If end of file is reached before reading the int
IOException
- If any other error occursDataOutput.writeInt(int)
public final String readLine() throws IOException
char
values by treating the byte read as the low
eight bits of the char
and using 0 as the high eight
bits. Because of this, it does not support the full 16-bit
Unicode character set.
The reading of bytes ends when either the end of file or a line
terminator is encountered. The bytes read are then returned as a
String
A line terminator is a byte sequence
consisting of either \r
, \n
or
\r\n
. These termination charaters are discarded and
are not returned as part of the string.
This method can read data that was written by an object implementing the
writeLine()
method in DataOutput
.
readLine
in interface DataInput
String
IOException
- If an error occursDataOutput
public final long readLong() throws IOException
long
value from an input stream
It operates by reading eight bytes from the stream and converting them to
a single Java long
. The bytes are stored most
significant byte first (i.e., "big endian") regardless of the native
host byte ordering.
As an example, if byte1
through byte8
represent
the first eight bytes read from the stream, they will be
transformed to an long
in the following manner:
(long)(((byte1 & 0xFF) << 56) + ((byte2 & 0xFF) << 48) +
((byte3 & 0xFF) << 40) + ((byte4 & 0xFF) << 32) +
((byte5 & 0xFF) << 24) + ((byte6 & 0xFF) << 16) +
((byte7 & 0xFF) << 8) + (byte8 & 0xFF)))
The value returned is in the range of -9223372036854775808 to 9223372036854775807.
This method can read an long
written by an object
implementing the writeLong()
method in the
DataOutput
interface.
readLong
in interface DataInput
long
value read
EOFException
- If end of file is reached before reading the long
IOException
- If any other error occursDataOutput.writeLong(long)
public final short readShort() throws IOException
short
. The
two bytes are stored most significant byte first (i.e., "big
endian") regardless of the native host byte ordering.
As an example, if byte1
and byte2
represent the first and second byte read from the stream
respectively, they will be transformed to a short
. in
the following manner:
(short)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF))
The value returned is in the range of -32768 to 32767.
This method can read a short
written by an object
implementing the writeShort()
method in the
DataOutput
interface.
readShort
in interface DataInput
short
value read
EOFException
- If end of file is reached before reading the value
IOException
- If any other error occursDataOutput.writeShort(int)
public final int readUnsignedByte() throws IOException
int
value from the stream. The value returned is in the range of 0 to
255.
This method can read an unsigned byte written by an object
implementing the writeUnsignedByte()
method in the
DataOutput
interface.
readUnsignedByte
in interface DataInput
int
.
EOFException
- If end of file is reached before reading the value
IOException
- If any other error occursDataOutput.writeByte(int)
public final int readUnsignedShort() throws IOException
int
The two bytes are stored most
significant byte first (i.e., "big endian") regardless of the native
host byte ordering.
As an example, if byte1
and byte2
represent the first and second byte read from the stream
respectively, they will be transformed to an int
in
the following manner:
(int)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))
The value returned is in the range of 0 to 65535.
This method can read an unsigned short written by an object
implementing the writeUnsignedShort()
method in the
DataOutput
interface.
readUnsignedShort
in interface DataInput
int
EOFException
- If end of file is reached before reading the value
IOException
- If any other error occursDataOutput.writeShort(int)
public final String readUTF() throws IOException
String
from an input stream that
is encoded in a modified UTF-8 format. This format has a leading
two byte sequence that contains the remaining number of bytes to
read. This two byte sequence is read using the
readUnsignedShort()
method of this interface.
After the number of remaining bytes have been determined, these
bytes are read an transformed into char
values.
These char
values are encoded in the stream using
either a one, two, or three byte format. The particular format
in use can be determined by examining the first byte read.
If the first byte has a high order bit of 0, then that character
consists on only one byte. This character value consists of
seven bits that are at positions 0 through 6 of the byte. As an
example, if byte1
is the byte read from the stream,
it would be converted to a char
like so:
(char)byte1
If the first byte has 110 as its high order bits, then the character consists of two bytes. The bits that make up the character value are in positions 0 through 4 of the first byte and bit positions 0 through 5 of the second byte. (The second byte should have 10 as its high order bits). These values are in most significant byte first (i.e., "big endian") order.
As an example, if byte1
and byte2
are
the first two bytes read respectively, and the high order bits of
them match the patterns which indicate a two byte character
encoding, then they would be converted to a Java
char
like so:
(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))
If the first byte has a 1110 as its high order bits, then the character consists of three bytes. The bits that make up the character value are in positions 0 through 3 of the first byte and bit positions 0 through 5 of the other two bytes. (The second and third bytes should have 10 as their high order bits). These values are in most significant byte first (i.e., "big endian") order.
As an example, if byte1
byte2
and
byte3
are the three bytes read, and the high order
bits of them match the patterns which indicate a three byte
character encoding, then they would be converted to a Java
char
like so:
(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) |
(byte3 & 0x3F))
Note that all characters are encoded in the method that requires
the fewest number of bytes with the exception of the character
with the value of \u0000
which is encoded as two
bytes. This is a modification of the UTF standard used to
prevent C language style NUL
values from appearing
in the byte stream.
This method can read data that was written by an object implementing the
writeUTF()
method in DataOutput
readUTF
in interface DataInput
String
read
EOFException
- If end of file is reached before reading
the String
UTFDataFormatException
- If the data is not in UTF-8 format
IOException
- If any other error occursDataOutput.writeUTF(java.lang.String)
public static final String readUTF(DataInput in) throws IOException
DataInput
source.
in
- The DataInput
source to read from
IOException
- If an error occursDataInput.readUTF()
public final int skipBytes(int n) throws IOException
skipBytes
in interface DataInput
n
- The requested number of bytes to skip.
IOException
- If an error occurs.
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