Class RandomAccessFile
- All Implemented Interfaces:
Closeable
,DataInput
,DataOutput
,AutoCloseable
getFilePointer
method and set by the seek
method.
It is generally true of all the reading routines in this class 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 stream has been closed.
- Since:
- 1.0
-
Constructor Summary
ConstructorDescriptionRandomAccessFile
(File file, String mode) Creates a random access file stream to read from, and optionally to write to, the file specified by theFile
argument.RandomAccessFile
(String pathname, String mode) Creates a random access file stream to read from, and optionally to write to, a file with the specified pathname. -
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
Closes this random access file stream and releases any system resources associated with the stream.final FileChannel
Returns the uniqueFileChannel
object associated with this file.final FileDescriptor
getFD()
Returns the opaque file descriptor object associated with this stream.long
Returns the current offset in this file.long
length()
Returns the length of this file.int
read()
Reads a byte of data from this file.int
read
(byte[] b) Reads up tob.length
bytes of data from this file into an array of bytes.int
read
(byte[] b, int off, int len) Reads up tolen
bytes of data from this file into an array of bytes.final boolean
Reads aboolean
from this file.final byte
readByte()
Reads a signed eight-bit value from this file.final char
readChar()
Reads a character from this file.final double
Reads adouble
from this file.final float
Reads afloat
from this file.final void
readFully
(byte[] b) Readsb.length
bytes from this file into the byte array, starting at the current file pointer.final void
readFully
(byte[] b, int off, int len) Reads exactlylen
bytes from this file into the byte array, starting at the current file pointer.final int
readInt()
Reads a signed 32-bit integer from this file.final String
readLine()
Reads the next line of text from this file.final long
readLong()
Reads a signed 64-bit integer from this file.final short
Reads a signed 16-bit number from this file.final int
Reads an unsigned eight-bit number from this file.final int
Reads an unsigned 16-bit number from this file.final String
readUTF()
Reads in a string from this file.void
seek
(long pos) Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.void
setLength
(long newLength) Sets the length of this file.int
skipBytes
(int n) Attempts to skip overn
bytes of input discarding the skipped bytes.void
write
(byte[] b) Writesb.length
bytes from the specified byte array to this file, starting at the current file pointer.void
write
(byte[] b, int off, int len) Writeslen
bytes from the specified byte array starting at offsetoff
to this file.void
write
(int b) Writes the specified byte to this file.final void
writeBoolean
(boolean v) Writes aboolean
to the file as a one-byte value.final void
writeByte
(int v) Writes abyte
to the file as a one-byte value.final void
writeBytes
(String s) Writes the string to the file as a sequence of bytes.final void
writeChar
(int v) Writes achar
to the file as a two-byte value, high byte first.final void
writeChars
(String s) Writes a string to the file as a sequence of characters.final void
writeDouble
(double v) Converts the double argument to along
using thedoubleToLongBits
method in classDouble
, and then writes thatlong
value to the file as an eight-byte quantity, high byte first.final void
writeFloat
(float v) Converts the float argument to anint
using thefloatToIntBits
method in classFloat
, and then writes thatint
value to the file as a four-byte quantity, high byte first.final void
writeInt
(int v) Writes anint
to the file as four bytes, high byte first.final void
writeLong
(long v) Writes along
to the file as eight bytes, high byte first.final void
writeShort
(int v) Writes ashort
to the file as two bytes, high byte first.final void
Writes a string to the file using modified UTF-8 encoding in a machine-independent manner.
-
Constructor Details
-
RandomAccessFile
Creates a random access file stream to read from, and optionally to write to, a file with the specified pathname. If the file exists it is opened; if it does not exist and write mode is specified, a new file is created. Symbolic links are automatically redirected to the target of the link. A newFileDescriptor
object is created to represent the connection to the file.The
mode
argument specifies the access mode with which the file is to be opened. The permitted values and their meanings are as specified for theRandomAccessFile(File,String)
constructor.If there is a security manager, its
checkRead
method is called with thepathname
argument as its argument to see if read access to the file is allowed. If the mode allows writing, the security manager'scheckWrite
method is also called with thepathname
argument as its argument to see if write access to the file is allowed.- Parameters:
pathname
- the system-dependent pathname stringmode
- the access mode- Throws:
IllegalArgumentException
- if the mode argument is not equal to one of"r"
,"rw"
,"rws"
, or"rwd"
FileNotFoundException
- if the mode is"r"
but the given pathname string does not denote an existing regular file, or if the mode begins with"rw"
but the given pathname string does not denote an existing, writable regular file and a new regular file of that pathname cannot be created, or if some other error occurs while opening or creating the fileSecurityException
- if a security manager exists and itscheckRead
method denies read access to the file or the mode is"rw"
and the security manager'scheckWrite
method denies write access to the file- See Also:
-
RandomAccessFile
Creates a random access file stream to read from, and optionally to write to, the file specified by theFile
argument. If the file exists it is opened; if it does not exist and write mode is specified, a new file is created. Symbolic links are automatically redirected to the target of the link. A newFileDescriptor
object is created to represent the connection to the file.The
mode
argument specifies the access mode in which the file is to be opened. The permitted values and their meanings are:Value Meaning "r"
Open for reading only. Invoking any of the write
methods of the resulting object will cause anIOException
to be thrown."rw"
Open for reading and writing. If the file does not already exist then an attempt will be made to create it. "rws"
Open for reading and writing, as with "rw"
, and also require that every update to the file's content or metadata be written synchronously to the underlying storage device."rwd"
Open for reading and writing, as with "rw"
, and also require that every update to the file's content be written synchronously to the underlying storage device."rws"
and"rwd"
modes work much like theforce(boolean)
method of theFileChannel
class, passing arguments oftrue
andfalse
, respectively, except that they always apply to every I/O operation and are therefore often more efficient. If the file resides on a local storage device then when an invocation of a method of this class returns it is guaranteed that all changes made to the file by that invocation will have been written to that device. This is useful for ensuring that critical information is not lost in the event of a system crash. If the file does not reside on a local device then no such guarantee is made.The
"rwd"
mode can be used to reduce the number of I/O operations performed. Using"rwd"
only requires updates to the file's content to be written to storage; using"rws"
requires updates to both the file's content and its metadata to be written, which generally requires at least one more low-level I/O operation.If there is a security manager, its
checkRead
method is called with the pathname of thefile
argument as its argument to see if read access to the file is allowed. If the mode allows writing, the security manager'scheckWrite
method is also called with the pathname of thefile
argument to see if write access to the file is allowed.- Parameters:
file
- the file objectmode
- the access mode, as described above- Throws:
IllegalArgumentException
- if the mode argument is not equal to one of"r"
,"rw"
,"rws"
, or"rwd"
FileNotFoundException
- if the mode is"r"
but the given file object does not denote an existing regular file, or if the mode begins with"rw"
but the given file object does not denote an existing, writable regular file and a new regular file of that pathname cannot be created, or if some other error occurs while opening or creating the fileSecurityException
- if a security manager exists and itscheckRead
method denies read access to the file or the mode is"rw"
and the security manager'scheckWrite
method denies write access to the file- See Also:
-
-
Method Details
-
getFD
Returns the opaque file descriptor object associated with this stream.- Returns:
- the file descriptor object associated with this stream.
- Throws:
IOException
- if an I/O error occurs.- See Also:
-
getChannel
Returns the uniqueFileChannel
object associated with this file.The
position
of the returned channel will always be equal to this object's file-pointer offset as returned by thegetFilePointer
method. Changing this object's file-pointer offset, whether explicitly or by reading or writing bytes, will change the position of the channel, and vice versa. Changing the file's length via this object will change the length seen via the file channel, and vice versa.- Returns:
- the file channel associated with this file
- Since:
- 1.4
-
read
Reads a byte of data from this file. The byte is returned as an integer in the range 0 to 255 (0x00-0x0ff
). This method blocks if no input is yet available.Although
RandomAccessFile
is not a subclass ofInputStream
, this method behaves in exactly the same way as theInputStream.read()
method ofInputStream
.- Returns:
- the next byte of data, or
-1
if the end of the file has been reached. - Throws:
IOException
- if an I/O error occurs. Not thrown if end-of-file has been reached.
-
read
Reads up tolen
bytes of data from this file into an array of bytes. This method blocks until at least one byte of input is available.Although
RandomAccessFile
is not a subclass ofInputStream
, this method behaves in exactly the same way as theInputStream.read(byte[], int, int)
method ofInputStream
.- Parameters:
b
- the buffer into which the data is read.off
- the start offset in arrayb
at which the data is written.len
- the maximum number of bytes read.- Returns:
- the total number of bytes read into the buffer, or
-1
if there is no more data because the end of the file has been reached. - Throws:
IOException
- If the first byte cannot be read for any reason other than end of file, or if the random access file has been closed, or if some other I/O error occurs.NullPointerException
- Ifb
isnull
.IndexOutOfBoundsException
- Ifoff
is negative,len
is negative, orlen
is greater thanb.length - off
-
read
Reads up tob.length
bytes of data from this file into an array of bytes. This method blocks until at least one byte of input is available.Although
RandomAccessFile
is not a subclass ofInputStream
, this method behaves in exactly the same way as theInputStream.read(byte[])
method ofInputStream
.- Parameters:
b
- the buffer into which the data is read.- Returns:
- the total number of bytes read into the buffer, or
-1
if there is no more data because the end of this file has been reached. - Throws:
IOException
- If the first byte cannot be read for any reason other than end of file, or if the random access file has been closed, or if some other I/O error occurs.NullPointerException
- Ifb
isnull
.
-
readFully
Readsb.length
bytes from this file into the byte array, starting at the current file pointer. This method reads repeatedly from the file until the requested number of bytes are read. This method blocks until the requested number of bytes are read, the end of the stream is detected, or an exception is thrown.- Specified by:
readFully
in interfaceDataInput
- Parameters:
b
- the buffer into which the data is read.- Throws:
NullPointerException
- ifb
isnull
.EOFException
- if this file reaches the end before reading all the bytes.IOException
- if an I/O error occurs.
-
readFully
Reads exactlylen
bytes from this file into the byte array, starting at the current file pointer. This method reads repeatedly from the file until the requested number of bytes are read. This method blocks until the requested number of bytes are read, the end of the stream is detected, or an exception is thrown.- Specified by:
readFully
in interfaceDataInput
- Parameters:
b
- the buffer into which the data is read.off
- the start offset into the data arrayb
.len
- the number of bytes to read.- Throws:
NullPointerException
- ifb
isnull
.IndexOutOfBoundsException
- ifoff
is negative,len
is negative, orlen
is greater thanb.length - off
.EOFException
- if this file reaches the end before reading all the bytes.IOException
- if an I/O error occurs.
-
skipBytes
Attempts to skip overn
bytes of input discarding the skipped bytes.This method 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 anEOFException
. The actual number of bytes skipped is returned. Ifn
is negative, no bytes are skipped.- Specified by:
skipBytes
in interfaceDataInput
- Parameters:
n
- the number of bytes to be skipped.- Returns:
- the actual number of bytes skipped.
- Throws:
IOException
- if an I/O error occurs.
-
write
Writes the specified byte to this file. The write starts at the current file pointer.- Specified by:
write
in interfaceDataOutput
- Parameters:
b
- thebyte
to be written.- Throws:
IOException
- if an I/O error occurs.
-
write
Writesb.length
bytes from the specified byte array to this file, starting at the current file pointer.- Specified by:
write
in interfaceDataOutput
- Parameters:
b
- the data.- Throws:
IOException
- if an I/O error occurs.
-
write
Writeslen
bytes from the specified byte array starting at offsetoff
to this file.- Specified by:
write
in interfaceDataOutput
- Parameters:
b
- the data.off
- the start offset in the data.len
- the number of bytes to write.- Throws:
IOException
- if an I/O error occurs.IndexOutOfBoundsException
- Ifoff
is negative,len
is negative, orlen
is greater thanb.length - off
-
getFilePointer
Returns the current offset in this file.- Returns:
- the offset from the beginning of the file, in bytes, at which the next read or write occurs.
- Throws:
IOException
- if an I/O error occurs.
-
seek
Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs. The offset may be set beyond the end of the file. Setting the offset beyond the end of the file does not change the file length. The file length will change only by writing after the offset has been set beyond the end of the file.- Parameters:
pos
- the offset position, measured in bytes from the beginning of the file, at which to set the file pointer.- Throws:
IOException
- ifpos
is less than0
or if an I/O error occurs.
-
length
Returns the length of this file.- Returns:
- the length of this file, measured in bytes.
- Throws:
IOException
- if an I/O error occurs.
-
setLength
Sets the length of this file.If the present length of the file as returned by the length method is greater than the desired length of the file specified by the
newLength
argument, then the file will be truncated.If the present length of the file is smaller than the desired length, then the file will be extended. The contents of the extended portion of the file are not defined.
If the present length of the file is equal to the desired length, then the file and its length will be unchanged.
In all cases, after this method returns, the file offset as returned by the getFilePointer method will equal the minimum of the desired length and the file offset before this method was called, even if the length is unchanged. In other words, this method constrains the file offset to the closed interval
[0,newLength]
.- Parameters:
newLength
- The desired length of the file- Throws:
IOException
- If the argument is negative or if some other I/O error occurs- Since:
- 1.2
-
close
Closes this random access file stream and releases any system resources associated with the stream. A closed random access file cannot perform input or output operations and cannot be reopened.If this file has an associated channel then the channel is closed as well.
- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- API Note:
- If this stream has an associated channel then this method will close the channel, which in turn will close this stream. Subclasses that override this method should be prepared to handle possible reentrant invocation.
- Throws:
IOException
- if an I/O error occurs.
-
readBoolean
Reads aboolean
from this file. This method reads a single byte from the file, starting at the current file pointer. A value of0
representsfalse
. Any other value representstrue
. This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.- Specified by:
readBoolean
in interfaceDataInput
- Returns:
- the
boolean
value read. - Throws:
EOFException
- if this file has reached the end.IOException
- if an I/O error occurs.
-
readByte
Reads a signed eight-bit value from this file. This method reads a byte from the file, starting from the current file pointer. If the byte read isb
, where0 <= b <= 255
, then the result is:(byte)(b)
This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readByte
in interfaceDataInput
- Returns:
- the next byte of this file as a signed eight-bit
byte
. - Throws:
EOFException
- if this file has reached the end.IOException
- if an I/O error occurs.
-
readUnsignedByte
Reads an unsigned eight-bit number from this file. This method reads a byte from this file, starting at the current file pointer, and returns that byte.This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readUnsignedByte
in interfaceDataInput
- Returns:
- the next byte of this file, interpreted as an unsigned eight-bit number.
- Throws:
EOFException
- if this file has reached the end.IOException
- if an I/O error occurs.
-
readShort
Reads a signed 16-bit number from this file. The method reads two bytes from this file, starting at the current file pointer. If the two bytes read, in order, areb1
andb2
, where each of the two values is between0
and255
, inclusive, then the result is equal to:(short)((b1 << 8) | b2)
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readShort
in interfaceDataInput
- Returns:
- the next two bytes of this file, interpreted as a signed 16-bit number.
- Throws:
EOFException
- if this file reaches the end before reading two bytes.IOException
- if an I/O error occurs.
-
readUnsignedShort
Reads an unsigned 16-bit number from this file. This method reads two bytes from the file, starting at the current file pointer. If the bytes read, in order, areb1
andb2
, where0 <= b1, b2 <= 255
, then the result is equal to:(b1 << 8) | b2
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readUnsignedShort
in interfaceDataInput
- Returns:
- the next two bytes of this file, interpreted as an unsigned 16-bit integer.
- Throws:
EOFException
- if this file reaches the end before reading two bytes.IOException
- if an I/O error occurs.
-
readChar
Reads a character from this file. This method reads two bytes from the file, starting at the current file pointer. If the bytes read, in order, areb1
andb2
, where0 <= b1, b2 <= 255
, then the result is equal to:(char)((b1 << 8) | b2)
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readChar
in interfaceDataInput
- Returns:
- the next two bytes of this file, interpreted as a
char
. - Throws:
EOFException
- if this file reaches the end before reading two bytes.IOException
- if an I/O error occurs.
-
readInt
Reads a signed 32-bit integer from this file. This method reads 4 bytes from the file, starting at the current file pointer. If the bytes read, in order, areb1
,b2
,b3
, andb4
, where0 <= b1, b2, b3, b4 <= 255
, then the result is equal to:(b1 << 24) | (b2 << 16) + (b3 << 8) + b4
This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readInt
in interfaceDataInput
- Returns:
- the next four bytes of this file, interpreted as an
int
. - Throws:
EOFException
- if this file reaches the end before reading four bytes.IOException
- if an I/O error occurs.
-
readLong
Reads a signed 64-bit integer from this file. This method reads eight bytes from the file, starting at the current file pointer. If the bytes read, in order, areb1
,b2
,b3
,b4
,b5
,b6
,b7
, andb8,
where:0 <= b1, b2, b3, b4, b5, b6, b7, b8 <= 255
then the result is equal to:
((long)b1 << 56) + ((long)b2 << 48) + ((long)b3 << 40) + ((long)b4 << 32) + ((long)b5 << 24) + ((long)b6 << 16) + ((long)b7 << 8) + b8
This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readLong
in interfaceDataInput
- Returns:
- the next eight bytes of this file, interpreted as a
long
. - Throws:
EOFException
- if this file reaches the end before reading eight bytes.IOException
- if an I/O error occurs.
-
readFloat
Reads afloat
from this file. This method reads anint
value, starting at the current file pointer, as if by thereadInt
method and then converts thatint
to afloat
using theintBitsToFloat
method in classFloat
.This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readFloat
in interfaceDataInput
- Returns:
- the next four bytes of this file, interpreted as a
float
. - Throws:
EOFException
- if this file reaches the end before reading four bytes.IOException
- if an I/O error occurs.- See Also:
-
readDouble
Reads adouble
from this file. This method reads along
value, starting at the current file pointer, as if by thereadLong
method and then converts thatlong
to adouble
using thelongBitsToDouble
method in classDouble
.This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readDouble
in interfaceDataInput
- Returns:
- the next eight bytes of this file, interpreted as a
double
. - Throws:
EOFException
- if this file reaches the end before reading eight bytes.IOException
- if an I/O error occurs.- See Also:
-
readLine
Reads the next line of text from this file. This method successively reads bytes from the file, starting at the current file pointer, until it reaches a line terminator or the end of the file. Each byte is converted into a character by taking the byte's value for the lower eight bits of the character and setting the high eight bits of the character to zero. This method does not, therefore, support the full Unicode character set.A line of text is terminated by a carriage-return character (
'\r'
), a newline character ('\n'
), a carriage-return character immediately followed by a newline character, or the end of the file. Line-terminating characters are discarded and are not included as part of the string returned.This method blocks until a newline character is read, a carriage return and the byte following it are read (to see if it is a newline), the end of the file is reached, or an exception is thrown.
- Specified by:
readLine
in interfaceDataInput
- Returns:
- the next line of text from this file, or null if end of file is encountered before even one byte is read.
- Throws:
IOException
- if an I/O error occurs.
-
readUTF
Reads in a string from this file. The string has been encoded using a modified UTF-8 format.The first two bytes are read, starting from the current file pointer, as if by
readUnsignedShort
. This value gives the number of following bytes that are in the encoded string, not the length of the resulting string. The following bytes are then interpreted as bytes encoding characters in the modified UTF-8 format and are converted into characters.This method blocks until all the bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readUTF
in interfaceDataInput
- Returns:
- a Unicode string.
- Throws:
EOFException
- if this file reaches the end before reading all the bytes.IOException
- if an I/O error occurs.UTFDataFormatException
- if the bytes do not represent valid modified UTF-8 encoding of a Unicode string.- See Also:
-
writeBoolean
Writes aboolean
to the file as a one-byte value. The valuetrue
is written out as the value(byte)1
; the valuefalse
is written out as the value(byte)0
. The write starts at the current position of the file pointer.- Specified by:
writeBoolean
in interfaceDataOutput
- Parameters:
v
- aboolean
value to be written.- Throws:
IOException
- if an I/O error occurs.
-
writeByte
Writes abyte
to the file as a one-byte value. The write starts at the current position of the file pointer.- Specified by:
writeByte
in interfaceDataOutput
- Parameters:
v
- abyte
value to be written.- Throws:
IOException
- if an I/O error occurs.
-
writeShort
Writes ashort
to the file as two bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeShort
in interfaceDataOutput
- Parameters:
v
- ashort
to be written.- Throws:
IOException
- if an I/O error occurs.
-
writeChar
Writes achar
to the file as a two-byte value, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeChar
in interfaceDataOutput
- Parameters:
v
- achar
value to be written.- Throws:
IOException
- if an I/O error occurs.
-
writeInt
Writes anint
to the file as four bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeInt
in interfaceDataOutput
- Parameters:
v
- anint
to be written.- Throws:
IOException
- if an I/O error occurs.
-
writeLong
Writes along
to the file as eight bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeLong
in interfaceDataOutput
- Parameters:
v
- along
to be written.- Throws:
IOException
- if an I/O error occurs.
-
writeFloat
Converts the float argument to anint
using thefloatToIntBits
method in classFloat
, and then writes thatint
value to the file as a four-byte quantity, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeFloat
in interfaceDataOutput
- Parameters:
v
- afloat
value to be written.- Throws:
IOException
- if an I/O error occurs.- See Also:
-
writeDouble
Converts the double argument to along
using thedoubleToLongBits
method in classDouble
, and then writes thatlong
value to the file as an eight-byte quantity, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeDouble
in interfaceDataOutput
- Parameters:
v
- adouble
value to be written.- Throws:
IOException
- if an I/O error occurs.- See Also:
-
writeBytes
Writes the string to the file as a sequence of bytes. Each character in the string is written out, in sequence, by discarding its high eight bits. The write starts at the current position of the file pointer.- Specified by:
writeBytes
in interfaceDataOutput
- Parameters:
s
- a string of bytes to be written.- Throws:
IOException
- if an I/O error occurs.
-
writeChars
Writes a string to the file as a sequence of characters. Each character is written to the data output stream as if by thewriteChar
method. The write starts at the current position of the file pointer.- Specified by:
writeChars
in interfaceDataOutput
- Parameters:
s
- aString
value to be written.- Throws:
IOException
- if an I/O error occurs.- See Also:
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writeUTF
Writes a string to the file using modified UTF-8 encoding in a machine-independent manner.First, two bytes are written to the file, starting at the current file pointer, as if by the
writeShort
method giving the number of bytes to follow. This value is the number of bytes actually written out, not the length of the string. Following the length, each character of the string is output, in sequence, using the modified UTF-8 encoding for each character.- Specified by:
writeUTF
in interfaceDataOutput
- Parameters:
str
- a string to be written.- Throws:
IOException
- if an I/O error occurs.
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