Closeable, DataInput, DataOutput, AutoCloseable
Instances of this class support both reading and writing to a random access file. A random access file behaves like a large array of bytes stored in the file system. There is a kind of cursor, or index into the implied array, called the
file pointer; input operations read bytes starting at the file pointer and advance the file pointer past the bytes read. If the random access file is created in read/write mode, then output operations are also available; output operations write bytes starting at the file pointer and advance the file pointer past the bytes written. Output operations that write past the current end of the implied array cause the array to be extended. The file pointer can be read by the
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.
Constructors
Creates a random access file stream to read from, and optionally to write to, the file specified by the
File
argument.
Creates a random access file stream to read from, and optionally to write to, a file with the specified name.
void
Closes this random access file stream and releases any system resources associated with the stream.
Returns the unique
FileChannel
object associated with this file.
Returns the opaque file descriptor object associated with this stream.
long
Returns the current offset in this file.
long
Returns the length of this file.
int
Reads a byte of data from this file.
int
Reads up to b.length bytes of data from this file into an array of bytes.
int
read(byte[] b, int off, int len)
Reads up to len bytes of data from this file into an array of bytes.
final boolean
Reads a boolean from this file.
final byte
Reads a signed eight-bit value from this file.
final char
Reads a character from this file.
final double
Reads a double from this file.
final float
Reads a float from this file.
final void
Reads b.length bytes from this file into the byte array, starting at the current file pointer.
final void
Reads exactly len bytes from this file into the byte array, starting at the current file pointer.
final int
Reads a signed 32-bit integer from this file.
Reads the next line of text from this file.
final long
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.
Reads in a string from this file.
void
Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.
void
Sets the length of this file.
int
Attempts to skip over n bytes of input discarding the skipped bytes.
void
Writes b.length bytes from the specified byte array to this file, starting at the current file pointer.
void
write(byte[] b, int off, int len)
Writes len bytes from the specified byte array starting at offset off to this file.
void
Writes the specified byte to this file.
final void
Writes a boolean to the file as a one-byte value.
final void
Writes a byte to the file as a one-byte value.
final void
Writes the string to the file as a sequence of bytes.
final void
Writes a char to the file as a two-byte value, high byte first.
final void
Writes a string to the file as a sequence of characters.
final void
Converts the double argument to a long using the doubleToLongBits method in class Double, and then writes that long value to the file as an eight-byte quantity, high byte first.
final void
Converts the float argument to an int using the floatToIntBits method in class Float, and then writes that int value to the file as a four-byte quantity, high byte first.
final void
Writes an int to the file as four bytes, high byte first.
final void
Writes a long to the file as eight bytes, high byte first.
final void
Writes a short to the file as two bytes, high byte first.
final void
Writes a string to the file using
modified UTF-8encoding in a machine-independent manner.
Methods declared in class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitCreates a random access file stream to read from, and optionally to write to, a file with the specified name. A new
FileDescriptor
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 the RandomAccessFile(File,String) constructor.
If there is a security manager, its checkRead method is called with the name argument as its argument to see if read access to the file is allowed. If the mode allows writing, the security manager's checkWrite method is also called with the name argument as its argument to see if write access to the file is allowed.
name - the system-dependent filename
mode - the access mode
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 string does not denote an existing regular file, or if the mode begins with "rw" but the given string does not denote an existing, writable regular file and a new regular file of that name cannot be created, or if some other error occurs while opening or creating the file
SecurityException - if a security manager exists and its checkRead method denies read access to the file or the mode is "rw" and the security manager's checkWrite method denies write access to the file
Creates a random access file stream to read from, and optionally to write to, the file specified by the
File
argument. A new
FileDescriptor
object is created to represent this file connection.
The mode argument specifies the access mode in which the file is to be opened. The permitted values and their meanings are:
"r" Open for reading only. Invoking any of the write methods of the resulting object will cause an IOException 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.
The
"rws"
and
"rwd"
modes work much like the
force(boolean)
method of the
FileChannel
class, passing arguments of
true
and
false
, 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 the file argument as its argument to see if read access to the file is allowed. If the mode allows writing, the security manager's checkWrite method is also called with the path argument to see if write access to the file is allowed.
file - the file object
mode - the access mode, as described above
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 name cannot be created, or if some other error occurs while opening or creating the file
SecurityException - if a security manager exists and its checkRead method denies read access to the file or the mode is "rw" and the security manager's checkWrite method denies write access to the file
Returns the opaque file descriptor object associated with this stream.
IOException - if an I/O error occurs.
Returns the unique
FileChannel
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 the getFilePointer 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.
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 of InputStream, this method behaves in exactly the same way as the InputStream.read() method of InputStream.
-1 if the end of the file has been reached.
IOException - if an I/O error occurs. Not thrown if end-of-file has been reached.
throws
IOExceptionReads up to
len
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 of InputStream, this method behaves in exactly the same way as the InputStream.read(byte[], int, int) method of InputStream.
b - the buffer into which the data is read.
off - the start offset in array b at which the data is written.
len - the maximum number of bytes read.
-1 if there is no more data because the end of the file has been reached.
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 - If b is null.
IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off
Reads up to
b.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 of InputStream, this method behaves in exactly the same way as the InputStream.read(byte[]) method of InputStream.
b - the buffer into which the data is read.
-1 if there is no more data because the end of this file has been reached.
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 - If b is null.
throws
IOExceptionReads b.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.
readFully in interface DataInput
b - the buffer into which the data is read.
NullPointerException - if b is null.
EOFException - if this file reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
throws
IOExceptionReads exactly len 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.
readFully in interface DataInput
b - the buffer into which the data is read.
off - the start offset into the data array b.
len - the number of bytes to read.
NullPointerException - if b is null.
IndexOutOfBoundsException - if off is negative, len is negative, or len is greater than b.length - off.
EOFException - if this file reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
Attempts to skip over
n
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 an EOFException. The actual number of bytes skipped is returned. If n is negative, no bytes are skipped.
skipBytes in interface DataInput
n - the number of bytes to be skipped.
IOException - if an I/O error occurs.
Writes the specified byte to this file. The write starts at the current file pointer.
write in interface DataOutput
b - the byte to be written.
IOException - if an I/O error occurs.
Writes b.length bytes from the specified byte array to this file, starting at the current file pointer.
write in interface DataOutput
b - the data.
IOException - if an I/O error occurs.
throws
IOExceptionWrites len bytes from the specified byte array starting at offset off to this file.
write in interface DataOutput
b - the data.
off - the start offset in the data.
len - the number of bytes to write.
IOException - if an I/O error occurs.
IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off
Returns the current offset in this file.
IOException - if an I/O error occurs.
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.
pos - the offset position, measured in bytes from the beginning of the file, at which to set the file pointer.
IOException - if pos is less than 0 or if an I/O error occurs.
Returns the length of this file.
IOException - if an I/O error occurs.
throws
IOExceptionSets the length of this file.
If the present length of the file as returned by the length method is greater than the newLength argument then the file will be truncated. In this case, if the file offset as returned by the getFilePointer method is greater than newLength then after this method returns the offset will be equal to newLength.
If the present length of the file as returned by the length method is smaller than the newLength argument then the file will be extended. In this case, the contents of the extended portion of the file are not defined.
newLength - The desired length of the file
IOException - If an I/O error occurs
If this file has an associated channel then the channel is closed as well.
close in interface AutoCloseable
close in interface Closeable
IOException - if an I/O error occurs.
Reads a boolean from this file. This method reads a single byte from the file, starting at the current file pointer. A value of 0 represents false. Any other value represents true. This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
readBoolean in interface DataInput
boolean value read.
EOFException - if this file has reached the end.
IOException - if an I/O error occurs.
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 is
b
, where
0 <= b <= 255
, then the result is:
This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
readByte in interface DataInput
byte.
EOFException - if this file has reached the end.
IOException - if an I/O error occurs.
() throws
IOExceptionThis method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
readUnsignedByte in interface DataInput
EOFException - if this file has reached the end.
IOException - if an I/O error occurs.
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, are
b1
and
b2
, where each of the two values is between
0
and
255
, inclusive, then the result is equal to:
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
readShort in interface DataInput
EOFException - if this file reaches the end before reading two bytes.
IOException - if an I/O error occurs.
() throws
IOExceptionReads 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, are
b1
and
b2
, where
0 <= b1, b2 <= 255
, then the result is equal to:
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
readUnsignedShort in interface DataInput
EOFException - if this file reaches the end before reading two bytes.
IOException - if an I/O error occurs.
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, are
b1
and
b2
, where
0 <= b1, b2 <= 255
, then the result is equal to:
This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
readChar in interface DataInput
char.
EOFException - if this file reaches the end before reading two bytes.
IOException - if an I/O error occurs.
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, are
b1
,
b2
,
b3
, and
b4
, where
0 <= 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.
readInt in interface DataInput
int.
EOFException - if this file reaches the end before reading four bytes.
IOException - if an I/O error occurs.
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, are
b1
,
b2
,
b3
,
b4
,
b5
,
b6
,
b7
, and
b8,
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.
readLong in interface DataInput
long.
EOFException - if this file reaches the end before reading eight bytes.
IOException - if an I/O error occurs.
Reads a
float
from this file. This method reads an
int
value, starting at the current file pointer, as if by the
readInt
method and then converts that
int
to a
float
using the
intBitsToFloat
method in class
Float
.
This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
readFloat in interface DataInput
float.
EOFException - if this file reaches the end before reading four bytes.
IOException - if an I/O error occurs.
Reads a
double
from this file. This method reads a
long
value, starting at the current file pointer, as if by the
readLong
method and then converts that
long
to a
double
using the
longBitsToDouble
method in class
Double
.
This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
readDouble in interface DataInput
double.
EOFException - if this file reaches the end before reading eight bytes.
IOException - if an I/O error occurs.
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.
readLine in interface DataInput
IOException - if an I/O error occurs.
Reads in a string from this file. The string has been encoded using a
modified UTF-8format.
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.
readUTF in interface DataInput
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.
throws
IOExceptionWrites a boolean to the file as a one-byte value. The value true is written out as the value (byte)1; the value false is written out as the value (byte)0. The write starts at the current position of the file pointer.
writeBoolean in interface DataOutput
v - a boolean value to be written.
IOException - if an I/O error occurs.
Writes a byte to the file as a one-byte value. The write starts at the current position of the file pointer.
writeByte in interface DataOutput
v - a byte value to be written.
IOException - if an I/O error occurs.
Writes a short to the file as two bytes, high byte first. The write starts at the current position of the file pointer.
writeShort in interface DataOutput
v - a short to be written.
IOException - if an I/O error occurs.
Writes a char to the file as a two-byte value, high byte first. The write starts at the current position of the file pointer.
writeChar in interface DataOutput
v - a char value to be written.
IOException - if an I/O error occurs.
Writes an int to the file as four bytes, high byte first. The write starts at the current position of the file pointer.
writeInt in interface DataOutput
v - an int to be written.
IOException - if an I/O error occurs.
Writes a long to the file as eight bytes, high byte first. The write starts at the current position of the file pointer.
writeLong in interface DataOutput
v - a long to be written.
IOException - if an I/O error occurs.
throws
IOExceptionConverts the float argument to an int using the floatToIntBits method in class Float, and then writes that int value to the file as a four-byte quantity, high byte first. The write starts at the current position of the file pointer.
writeFloat in interface DataOutput
v - a float value to be written.
IOException - if an I/O error occurs.
throws
IOExceptionConverts the double argument to a long using the doubleToLongBits method in class Double, and then writes that long value to the file as an eight-byte quantity, high byte first. The write starts at the current position of the file pointer.
writeDouble in interface DataOutput
v - a double value to be written.
IOException - if an I/O error occurs.
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.
writeBytes in interface DataOutput
s - a string of bytes to be written.
IOException - if an I/O error occurs.
Writes a string to the file as a sequence of characters. Each character is written to the data output stream as if by the writeChar method. The write starts at the current position of the file pointer.
writeChars in interface DataOutput
s - a String value to be written.
IOException - if an I/O error occurs.
Writes a string to the file using
modified UTF-8encoding 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.
writeUTF in interface DataOutput
str - a string to be written.
IOException - if an I/O error occurs.
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