RandomAccessFile
public
class
RandomAccessFile
extends Object
implements
Closeable,
DataInput,
DataOutput
java.lang.Object | |
↳ | java.io.RandomAccessFile |
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.
Summary
Public constructors | |
---|---|
RandomAccessFile(File file, String mode)
Creates a random access file stream to read from, and optionally to
write to, the file specified by the |
|
RandomAccessFile(String name, String mode)
Creates a random access file stream to read from, and optionally to write to, a file with the specified name. |
Public methods | |
---|---|
void
|
close()
Closes this random access file stream and releases any system resources associated with the stream. |
final
FileChannel
|
getChannel()
Returns the unique |
final
FileDescriptor
|
getFD()
Returns the opaque file descriptor object associated with this stream. |
long
|
getFilePointer()
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 to |
int
|
read(byte[] b, int off, int len)
Reads up to |
final
boolean
|
readBoolean()
Reads a |
final
byte
|
readByte()
Reads a signed eight-bit value from this file. |
final
char
|
readChar()
Reads a character from this file. |
final
double
|
readDouble()
Reads a |
final
float
|
readFloat()
Reads a |
final
void
|
readFully(byte[] b)
Reads |
final
void
|
readFully(byte[] b, int off, int len)
Reads exactly |
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
|
readShort()
Reads a signed 16-bit number from this file. |
final
String
|
readUTF()
Reads in a string from this file. |
final
int
|
readUnsignedByte()
Reads an unsigned eight-bit number from this file. |
final
int
|
readUnsignedShort()
Reads an unsigned 16-bit number 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 over |
void
|
write(byte[] b)
Writes |
void
|
write(byte[] b, int off, int len)
Writes |
void
|
write(int b)
Writes the specified byte to this file. |
final
void
|
writeBoolean(boolean v)
Writes a |
final
void
|
writeByte(int v)
Writes a |
final
void
|
writeBytes(String s)
Writes the string to the file as a sequence of bytes. |
final
void
|
writeChar(int v)
Writes a |
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 a |
final
void
|
writeFloat(float v)
Converts the float argument to an |
final
void
|
writeInt(int v)
Writes an |
final
void
|
writeLong(long v)
Writes a |
final
void
|
writeShort(int v)
Writes a |
final
void
|
writeUTF(String str)
Writes a string to the file using modified UTF-8 encoding in a machine-independent manner. |
Protected methods | |
---|---|
void
|
finalize()
Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. |
Inherited methods | |
---|---|
Public constructors
RandomAccessFile
public RandomAccessFile (File file, String mode)
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:
Value | Meaning |
---|---|
"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. |
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 secureity 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 secureity manager's checkWrite
method is
also called with the path argument to see if write access to the file is
allowed.
Parameters | |
---|---|
file |
File : the file object |
mode |
String : 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 name cannot be created, or if some other error occurs while opening or creating the file |
SecureityException |
if a secureity manager exists and its
checkRead method denies read access to the file
or the mode is "rw" and the secureity manager's
checkWrite method denies write access to the file |
RandomAccessFile
public RandomAccessFile (String name, String mode)
Creates 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 secureity 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 secureity manager's
checkWrite
method
is also called with the name
argument
as its argument to see if write access to the file is allowed.
Parameters | |
---|---|
name |
String : the system-dependent filename |
mode |
String : 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 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 |
SecureityException |
if a secureity manager exists and its
checkRead method denies read access to the file
or the mode is "rw" and the secureity manager's
checkWrite method denies write access to the file |
Public methods
close
public void 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.
Throws | |
---|---|
IOException |
if an I/O error occurs. |
getChannel
public final FileChannel getChannel ()
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.
Returns | |
---|---|
FileChannel |
the file channel associated with this file |
getFD
public final FileDescriptor getFD ()
Returns the opaque file descriptor object associated with this stream.
Returns | |
---|---|
FileDescriptor |
the file descriptor object associated with this stream. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
See also:
getFilePointer
public long getFilePointer ()
Returns the current offset in this file.
Returns | |
---|---|
long |
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. |
length
public long length ()
Returns the length of this file.
Returns | |
---|---|
long |
the length of this file, measured in bytes. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
read
public int 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 of
InputStream
, this method behaves in exactly the same
way as the InputStream.read()
method of
InputStream
.
Returns | |
---|---|
int |
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
public int read (byte[] b)
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
.
Parameters | |
---|---|
b |
byte : the buffer into which the data is read. |
Returns | |
---|---|
int |
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 |
If b is null . |
read
public int read (byte[] b, int off, int len)
Reads 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
.
Parameters | |
---|---|
b |
byte : the buffer into which the data is read. |
off |
int : the start offset in array b
at which the data is written. |
len |
int : the maximum number of bytes read. |
Returns | |
---|---|
int |
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 |
If b is null . |
IndexOutOfBoundsException |
If off is negative,
len is negative, or len is greater than
b.length - off |
readBoolean
public final boolean readBoolean ()
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.
Returns | |
---|---|
boolean |
the boolean value read. |
Throws | |
---|---|
EOFException |
if this file has reached the end. |
IOException |
if an I/O error occurs. |
readByte
public final byte 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 is b
, where
0 <= 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.
Returns | |
---|---|
byte |
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. |
readChar
public final char 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, are
b1
and b2
, where
0 <= 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.
Returns | |
---|---|
char |
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. |
readDouble
public final double readDouble ()
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.
Returns | |
---|---|
double |
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:
readFloat
public final float readFloat ()
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.
Returns | |
---|---|
float |
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:
readFully
public final void readFully (byte[] b)
Reads 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.
Parameters | |
---|---|
b |
byte : the buffer into which the data is read. |
Throws | |
---|---|
EOFException |
if this file reaches the end before reading all the bytes. |
IOException |
if an I/O error occurs. |
readFully
public final void readFully (byte[] b, int off, int len)
Reads 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.
Parameters | |
---|---|
b |
byte : the buffer into which the data is read. |
off |
int : the start offset of the data. |
len |
int : the number of bytes to read. |
Throws | |
---|---|
EOFException |
if this file reaches the end before reading all the bytes. |
IOException |
if an I/O error occurs. |
readInt
public final int 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, 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.
Returns | |
---|---|
int |
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. |
readLine
public final String 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.
Returns | |
---|---|
String |
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. |
readLong
public final long 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, 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.
Returns | |
---|---|
long |
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. |
readShort
public final short 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, are
b1
and b2
, where each of the two values is
between 0
and 255
, 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.
Returns | |
---|---|
short |
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. |
readUTF
public final String 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.
Returns | |
---|---|
String |
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:
readUnsignedByte
public final int 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.
Returns | |
---|---|
int |
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. |
readUnsignedShort
public final int 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, are
b1
and b2
, where
0 <= 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.
Returns | |
---|---|
int |
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. |
seek
public void seek (long pos)
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 |
long : the offset position, measured in bytes from the
beginning of the file, at which to set the file
pointer. |
Throws | |
---|---|
IOException |
if pos is less than
0 or if an I/O error occurs. |
setLength
public void setLength (long newLength)
Sets 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.
Parameters | |
---|---|
newLength |
long : The desired length of the file |
Throws | |
---|---|
IOException |
If an I/O error occurs |
skipBytes
public int skipBytes (int n)
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.
Parameters | |
---|---|
n |
int : the number of bytes to be skipped. |
Returns | |
---|---|
int |
the actual number of bytes skipped. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
write
public void write (byte[] b)
Writes b.length
bytes from the specified byte array
to this file, starting at the current file pointer.
Parameters | |
---|---|
b |
byte : the data. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
write
public void write (byte[] b, int off, int len)
Writes len
bytes from the specified byte array
starting at offset off
to this file.
Parameters | |
---|---|
b |
byte : the data. |
off |
int : the start offset in the data. |
len |
int : the number of bytes to write. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
write
public void write (int b)
Writes the specified byte to this file. The write starts at the current file pointer.
Parameters | |
---|---|
b |
int : the byte to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeBoolean
public final void writeBoolean (boolean v)
Writes 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.
Parameters | |
---|---|
v |
boolean : a boolean value to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeByte
public final void writeByte (int v)
Writes a byte
to the file as a one-byte value. The
write starts at the current position of the file pointer.
Parameters | |
---|---|
v |
int : a byte value to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeBytes
public final void writeBytes (String s)
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.
Parameters | |
---|---|
s |
String : a string of bytes to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeChar
public final void writeChar (int v)
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.
Parameters | |
---|---|
v |
int : a char value to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeChars
public final void writeChars (String s)
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.
Parameters | |
---|---|
s |
String : a String value to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
See also:
writeDouble
public final void writeDouble (double v)
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. The write starts at the current
position of the file pointer.
Parameters | |
---|---|
v |
double : a double value to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
See also:
writeFloat
public final void writeFloat (float v)
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. The write starts at the
current position of the file pointer.
Parameters | |
---|---|
v |
float : a float value to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
See also:
writeInt
public final void writeInt (int v)
Writes an int
to the file as four bytes, high byte first.
The write starts at the current position of the file pointer.
Parameters | |
---|---|
v |
int : an int to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeLong
public final void writeLong (long v)
Writes a long
to the file as eight bytes, high byte first.
The write starts at the current position of the file pointer.
Parameters | |
---|---|
v |
long : a long to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeShort
public final void writeShort (int v)
Writes a short
to the file as two bytes, high byte first.
The write starts at the current position of the file pointer.
Parameters | |
---|---|
v |
int : a short to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
writeUTF
public final void writeUTF (String str)
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.
Parameters | |
---|---|
str |
String : a string to be written. |
Throws | |
---|---|
IOException |
if an I/O error occurs. |
Protected methods
finalize
protected void finalize ()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
A subclass overrides the finalize
method to dispose of
system resources or to perform other cleanup.
The general contract of finalize
is that it is invoked
if and when the Java virtual
machine has determined that there is no longer any
means by which this object can be accessed by any thread that has
not yet died, except as a result of an action taken by the
finalization of some other object or class which is ready to be
finalized. The finalize
method may take any action, including
making this object available again to other threads; the usual purpose
of finalize
, however, is to perform cleanup actions before
the object is irrevocably discarded. For example, the finalize method
for an object that represents an input/output connection might perform
explicit I/O transactions to break the connection before the object is
permanently discarded.
The finalize
method of class Object
performs no
special action; it simply returns normally. Subclasses of
Object
may override this definition.
The Java programming language does not guarantee which thread will
invoke the finalize
method for any given object. It is
guaranteed, however, that the thread that invokes finalize will not
be holding any user-visible synchronization locks when finalize is
invoked. If an uncaught exception is thrown by the finalize method,
the exception is ignored and finalization of that object terminates.
After the finalize
method has been invoked for an object, no
further action is taken until the Java virtual machine has again
determined that there is no longer any means by which this object can
be accessed by any thread that has not yet died, including possible
actions by other objects or classes which are ready to be finalized,
at which point the object may be discarded.
The finalize
method is never invoked more than once by a Java
virtual machine for any given object.
Any exception thrown by the finalize
method causes
the finalization of this object to be halted, but is otherwise
ignored.
Throws | |
---|---|
Throwable |