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
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Constructor Summary
ConstructorsConstructorDescriptionRandomAccessFile(File file, String mode) Creates a random access file stream to read from, and optionally to write to, the file specified by theFileargument.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 TypeMethodDescriptionvoidclose()Closes this random access file stream and releases any system resources associated with the stream.final FileChannelReturns the uniqueFileChannelobject associated with this file.final FileDescriptorgetFD()Returns the opaque file descriptor object associated with this stream.longReturns the current offset in this file.longlength()Returns the length of this file.intread()Reads a byte of data from this file.intread(byte[] b) Reads up tob.lengthbytes of data from this file into an array of bytes.intread(byte[] b, int off, int len) Reads up tolenbytes of data from this file into an array of bytes.final booleanReads abooleanfrom this file.final bytereadByte()Reads a signed eight-bit value from this file.final charreadChar()Reads a character from this file.final doubleReads adoublefrom this file.final floatReads afloatfrom this file.final voidreadFully(byte[] b) Readsb.lengthbytes from this file into the byte array, starting at the current file pointer.final voidreadFully(byte[] b, int off, int len) Reads exactlylenbytes from this file into the byte array, starting at the current file pointer.final intreadInt()Reads a signed 32-bit integer from this file.final StringreadLine()Reads the next line of text from this file.final longreadLong()Reads a signed 64-bit integer from this file.final shortReads a signed 16-bit number from this file.final intReads an unsigned eight-bit number from this file.final intReads an unsigned 16-bit number from this file.final StringreadUTF()Reads in a string from this file.voidseek(long pos) Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.voidsetLength(long newLength) Sets the length of this file.intskipBytes(int n) Attempts to skip overnbytes of input discarding the skipped bytes.voidwrite(byte[] b) Writesb.lengthbytes from the specified byte array to this file, starting at the current file pointer.voidwrite(byte[] b, int off, int len) Writeslenbytes from the specified byte array starting at offsetoffto this file.voidwrite(int b) Writes the specified byte to this file.final voidwriteBoolean(boolean v) Writes abooleanto the file as a one-byte value.final voidwriteByte(int v) Writes abyteto the file as a one-byte value.final voidwriteBytes(String s) Writes the string to the file as a sequence of bytes.final voidwriteChar(int v) Writes acharto the file as a two-byte value, high byte first.final voidwriteChars(String s) Writes a string to the file as a sequence of characters.final voidwriteDouble(double v) Converts the double argument to alongusing thedoubleToLongBitsmethod in classDouble, and then writes thatlongvalue to the file as an eight-byte quantity, high byte first.final voidwriteFloat(float v) Converts the float argument to anintusing thefloatToIntBitsmethod in classFloat, and then writes thatintvalue to the file as a four-byte quantity, high byte first.final voidwriteInt(int v) Writes anintto the file as four bytes, high byte first.final voidwriteLong(long v) Writes alongto the file as eight bytes, high byte first.final voidwriteShort(int v) Writes ashortto the file as two bytes, high byte first.final voidWrites a string to the file using modified UTF-8 encoding in a machine-independent manner.
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Constructor Details
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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 newFileDescriptorobject is created to represent the connection to the file.The
modeargument 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.- 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 file
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RandomAccessFile
Creates a random access file stream to read from, and optionally to write to, the file specified by theFileargument. 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 newFileDescriptorobject is created to represent the connection to the file.The
modeargument specifies the access mode in which the file is to be opened. The permitted values and their meanings are:
TheValue Meaning "r"Open for reading only. Invoking any of the writemethods of the resulting object will cause anIOExceptionto 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 theFileChannelclass, passing arguments oftrueandfalse, 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.- 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 file- See Also:
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Method Details
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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:
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getChannel
Returns the uniqueFileChannelobject associated with this file.The
positionof the returned channel will always be equal to this object's file-pointer offset as returned by thegetFilePointermethod. 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
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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
RandomAccessFileis not a subclass ofInputStream, this method behaves in exactly the same way as theInputStream.read()method ofInputStream.- Returns:
- the next byte of data, or
-1if 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.
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read
Reads up tolenbytes of data from this file into an array of bytes. This method blocks until at least one byte of input is available.Although
RandomAccessFileis 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 arraybat which the data is written.len- the maximum number of bytes read.- Returns:
- the total number of bytes read into the buffer, or
-1if 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- Ifbisnull.IndexOutOfBoundsException- Ifoffis negative,lenis negative, orlenis greater thanb.length - off
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read
Reads up tob.lengthbytes of data from this file into an array of bytes. This method blocks until at least one byte of input is available.Although
RandomAccessFileis 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
-1if 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- Ifbisnull.
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readFully
Readsb.lengthbytes 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:
readFullyin interfaceDataInput- Parameters:
b- the buffer into which the data is read.- Throws:
NullPointerException- ifbisnull.EOFException- if this file reaches the end before reading all the bytes.IOException- if an I/O error occurs.
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readFully
Reads exactlylenbytes 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:
readFullyin 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- ifbisnull.IndexOutOfBoundsException- ifoffis negative,lenis negative, orlenis greater thanb.length - off.EOFException- if this file reaches the end before reading all the bytes.IOException- if an I/O error occurs.
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skipBytes
Attempts to skip overnbytes 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
nbytes have been skipped is only one possibility. This method never throws anEOFException. The actual number of bytes skipped is returned. Ifnis negative, no bytes are skipped.- Specified by:
skipBytesin 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.
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write
Writes the specified byte to this file. The write starts at the current file pointer.- Specified by:
writein interfaceDataOutput- Parameters:
b- thebyteto be written.- Throws:
IOException- if an I/O error occurs.
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write
Writesb.lengthbytes from the specified byte array to this file, starting at the current file pointer.- Specified by:
writein interfaceDataOutput- Parameters:
b- the data.- Throws:
IOException- if an I/O error occurs.
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write
Writeslenbytes from the specified byte array starting at offsetoffto this file.- Specified by:
writein 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- Ifoffis negative,lenis negative, orlenis greater thanb.length - off
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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.
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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- ifposis less than0or if an I/O error occurs.
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length
Returns the length of this file.- Returns:
- the length of this file, measured in bytes.
- Throws:
IOException- if an I/O error occurs.
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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
newLengthargument, 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
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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:
closein interfaceAutoCloseable- Specified by:
closein 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.
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readBoolean
Reads abooleanfrom this file. This method reads a single byte from the file, starting at the current file pointer. A value of0representsfalse. 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:
readBooleanin interfaceDataInput- Returns:
- the
booleanvalue read. - Throws:
EOFException- if this file has reached the end.IOException- if an I/O error occurs.
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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:
readBytein 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.
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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:
readUnsignedBytein 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.
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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, areb1andb2, where each of the two values is between0and255, 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:
readShortin 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.
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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, areb1andb2, where0 <= b1, b2 <= 255, then the result is equal to:(b1 << 8) | b2This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readUnsignedShortin 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.
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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, areb1andb2, 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:
readCharin 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.
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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) + b4This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readIntin 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.
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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 <= 255then 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) + b8This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
readLongin 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.
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readFloat
Reads afloatfrom this file. This method reads anintvalue, starting at the current file pointer, as if by thereadIntmethod and then converts thatintto afloatusing theintBitsToFloatmethod 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:
readFloatin 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:
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readDouble
Reads adoublefrom this file. This method reads alongvalue, starting at the current file pointer, as if by thereadLongmethod and then converts thatlongto adoubleusing thelongBitsToDoublemethod 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:
readDoublein 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:
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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:
readLinein 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.
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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:
readUTFin 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:
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writeBoolean
Writes abooleanto the file as a one-byte value. The valuetrueis written out as the value(byte)1; the valuefalseis written out as the value(byte)0. The write starts at the current position of the file pointer.- Specified by:
writeBooleanin interfaceDataOutput- Parameters:
v- abooleanvalue to be written.- Throws:
IOException- if an I/O error occurs.
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writeByte
Writes abyteto the file as a one-byte value. The write starts at the current position of the file pointer.- Specified by:
writeBytein interfaceDataOutput- Parameters:
v- abytevalue to be written.- Throws:
IOException- if an I/O error occurs.
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writeShort
Writes ashortto the file as two bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeShortin interfaceDataOutput- Parameters:
v- ashortto be written.- Throws:
IOException- if an I/O error occurs.
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writeChar
Writes acharto the file as a two-byte value, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeCharin interfaceDataOutput- Parameters:
v- acharvalue to be written.- Throws:
IOException- if an I/O error occurs.
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writeInt
Writes anintto the file as four bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeIntin interfaceDataOutput- Parameters:
v- anintto be written.- Throws:
IOException- if an I/O error occurs.
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writeLong
Writes alongto the file as eight bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeLongin interfaceDataOutput- Parameters:
v- alongto be written.- Throws:
IOException- if an I/O error occurs.
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writeFloat
Converts the float argument to anintusing thefloatToIntBitsmethod in classFloat, and then writes thatintvalue to the file as a four-byte quantity, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeFloatin interfaceDataOutput- Parameters:
v- afloatvalue to be written.- Throws:
IOException- if an I/O error occurs.- See Also:
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writeDouble
Converts the double argument to alongusing thedoubleToLongBitsmethod in classDouble, and then writes thatlongvalue to the file as an eight-byte quantity, high byte first. The write starts at the current position of the file pointer.- Specified by:
writeDoublein interfaceDataOutput- Parameters:
v- adoublevalue to be written.- Throws:
IOException- if an I/O error occurs.- See Also:
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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:
writeBytesin interfaceDataOutput- Parameters:
s- a string of bytes to be written.- Throws:
IOException- if an I/O error occurs.
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writeChars
Writes a string to the file as a sequence of characters. Each character is written to the data output stream as if by thewriteCharmethod. The write starts at the current position of the file pointer.- Specified by:
writeCharsin interfaceDataOutput- Parameters:
s- aStringvalue 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
writeShortmethod 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:
writeUTFin interfaceDataOutput- Parameters:
str- a string to be written.- Throws:
IOException- if an I/O error occurs.
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