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FlexDoc/Javadoc 2.0 Demo Java Doc |
Class RandomAccessFile
java.io.RandomAccessFile
All Implemented Interfaces:
public class 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.
Since:
1.0
Constructor Summary |
Creates a random access file stream to read from, and optionally to
write to, the file specified by the File argument.
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Creates a random access file stream to read from, and optionally
to write to, a file with the specified name.
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Method Summary |
void |
Closes this random access file stream and releases any system
resources associated with the stream.
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Returns the unique FileChannel
object associated with this file.
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Returns the opaque file descriptor object associated with this
stream.
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long |
Returns the current offset in this file.
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long |
Returns the length of this file.
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int |
Reads a byte of data from this file.
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int |
Reads up to b.length bytes of data from this file
into an array of bytes.
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int |
read(byte[] b, int off, int len)
Reads up to len bytes of data from this file into an
array of bytes.
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final boolean |
Reads a boolean from this file.
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final byte |
Reads a signed eight-bit value from this file.
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final char |
Reads a character from this file.
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final double |
Reads a double from this file.
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final float |
Reads a float from this file.
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final void |
Reads b.length bytes from this file into the byte
array, starting at the current file pointer.
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final void |
Reads exactly len bytes from this file into the byte
array, starting at the current file pointer.
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final int |
Reads a signed 32-bit integer from this file.
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Reads the next line of text from this file.
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final long |
Reads a signed 64-bit integer from this file.
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final short |
Reads a signed 16-bit number from this file.
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final int |
Reads an unsigned eight-bit number from this file.
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final int |
Reads an unsigned 16-bit number from this file.
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Reads in a string from this file.
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void |
Sets the file-pointer offset, measured from the beginning of this
file, at which the next read or write occurs.
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void |
Sets the length of this file.
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int |
Attempts to skip over n bytes of input discarding the
skipped bytes.
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void |
Writes b.length bytes from the specified byte array
to this file, starting at the current file pointer.
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void |
write(byte[] b, int off, int len)
Writes len bytes from the specified byte array
starting at offset off to this file.
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void |
Writes the specified byte to this file.
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final void |
Writes a boolean to the file as a one-byte value.
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final void |
Writes a byte to the file as a one-byte value.
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final void |
Writes the string to the file as a sequence of bytes.
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final void |
Writes a char to the file as a two-byte value, high
byte first.
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final void |
Writes a string to the file as a sequence of characters.
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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.
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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.
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final void |
Writes an int to the file as four bytes, high byte first.
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final void |
Writes a long to the file as eight bytes, high byte first.
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final void |
Writes a short to the file as two bytes, high byte first.
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final void |
Writes a string to the file using
modified UTF-8
encoding in a machine-independent manner.
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Methods inherited from class java.lang. Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
public RandomAccessFile |
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throws |
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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 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.
Parameters:
name - the system-dependent filename
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
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
See Also:
public RandomAccessFile |
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throws |
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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:
Access mode permitted values and meanings
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. |
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.
Parameters:
file - the file object
mode - 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
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
See Also:
Returns the opaque file descriptor object associated with this
stream.
Returns:
the file descriptor object associated with this stream.
Throws:
See Also:
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:
the file channel associated with this file
Since:
1.4
public int read |
() |
throws |
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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:
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.
public int read |
(byte[] b, int off, int len) |
throws |
|
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 - 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.
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.
public int read |
(byte[] b) |
throws |
|
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 - 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.
public final void readFully |
(byte[] b) |
throws |
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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.
Specified by:
Parameters:
b - the buffer into which the data is read.
Throws:
public final void readFully |
(byte[] b, int off, int len) |
throws |
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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.
Specified by:
Parameters:
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.
Throws:
public int skipBytes |
(int n) |
throws |
|
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.
Specified by:
Parameters:
n - the number of bytes to be skipped.
Returns:
the actual number of bytes skipped.
Throws:
public void write |
(int b) |
throws |
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Writes the specified byte to this file. The write starts at
the current file pointer.
Specified by:
Parameters:
b - the byte to be written.
Throws:
public void write |
(byte[] b) |
throws |
|
Writes
b.length bytes from the specified byte array
to this file, starting at the current file pointer.
Specified by:
Parameters:
b - the data.
Throws:
public void write |
(byte[] b, int off, int len) |
throws |
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Writes
len bytes from the specified byte array
starting at offset
off to this file.
Specified by:
Parameters:
b - the data.
off - the start offset in the data.
len - the number of bytes to write.
Throws:
public long getFilePointer |
() |
throws |
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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:
public void seek |
(long pos) |
throws |
|
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 - if
pos is less than
0 or if an I/O error occurs.
public long length |
() |
throws |
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Returns the length of this file.
Returns:
the length of this file, measured in bytes.
Throws:
public void setLength |
(long newLength) |
throws |
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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 - The desired length of the file
Throws:
Since:
1.2
public void close |
() |
throws |
|
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:
Throws:
public final boolean readBoolean |
() |
throws |
|
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.
Specified by:
Returns:
the boolean value read.
Throws:
public final byte readByte |
() |
throws |
|
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.
Specified by:
Returns:
the next byte of this file as a signed eight-bit
byte.
Throws:
public final int readUnsignedByte |
() |
throws |
|
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:
Returns:
the next byte of this file, interpreted as an unsigned
eight-bit number.
Throws:
public final short readShort |
() |
throws |
|
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.
Specified by:
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.
public final int readUnsignedShort |
() |
throws |
|
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.
Specified by:
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.
public final char readChar |
() |
throws |
|
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.
Specified by:
Returns:
the next two bytes of this file, interpreted as a
char.
Throws:
EOFException - if this file reaches the end before reading
two bytes.
public final int readInt |
() |
throws |
|
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.
Specified by:
Returns:
the next four bytes of this file, interpreted as an
int.
Throws:
EOFException - if this file reaches the end before reading
four bytes.
public final long readLong |
() |
throws |
|
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.
Specified by:
Returns:
the next eight bytes of this file, interpreted as a
long.
Throws:
EOFException - if this file reaches the end before reading
eight bytes.
public final float readFloat |
() |
throws |
|
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.
Specified by:
Returns:
the next four bytes of this file, interpreted as a
float.
Throws:
EOFException - if this file reaches the end before reading
four bytes.
See Also:
public final double readDouble |
() |
throws |
|
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.
Specified by:
Returns:
the next eight bytes of this file, interpreted as a
double.
Throws:
EOFException - if this file reaches the end before reading
eight bytes.
See Also:
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:
Returns:
the next line of text from this file, or null if end
of file is encountered before even one byte is read.
Throws:
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:
Returns:
a Unicode string.
Throws:
EOFException - if this file reaches the end before
reading all the bytes.
See Also:
public final void writeBoolean |
(boolean v) |
throws |
|
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.
Specified by:
Parameters:
v - a boolean value to be written.
Throws:
public final void writeByte |
(int v) |
throws |
|
Writes a
byte to the file as a one-byte value. The
write starts at the current position of the file pointer.
Specified by:
Parameters:
v - a byte value to be written.
Throws:
public final void writeShort |
(int v) |
throws |
|
Writes a
short to the file as two bytes, high byte first.
The write starts at the current position of the file pointer.
Specified by:
Parameters:
v - a short to be written.
Throws:
public final void writeChar |
(int v) |
throws |
|
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.
Specified by:
Parameters:
v - a char value to be written.
Throws:
public final void writeInt |
(int v) |
throws |
|
Writes an
int to the file as four bytes, high byte first.
The write starts at the current position of the file pointer.
Specified by:
Parameters:
v - an int to be written.
Throws:
public final void writeLong |
(long v) |
throws |
|
Writes a
long to the file as eight bytes, high byte first.
The write starts at the current position of the file pointer.
Specified by:
Parameters:
v - a long to be written.
Throws:
public final void writeFloat |
(float v) |
throws |
|
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.
Specified by:
Parameters:
v - a float value to be written.
Throws:
See Also:
public final void writeDouble |
(double v) |
throws |
|
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.
Specified by:
Parameters:
v - a double value to be written.
Throws:
See Also:
public final void writeBytes |
|
throws |
|
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:
Parameters:
s - a string of bytes to be written.
Throws:
public final void writeChars |
|
throws |
|
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.
Specified by:
Parameters:
s - a String value to be written.
Throws:
See Also:
public final void writeUTF |
|
throws |
|
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:
Parameters:
str - a string to be written.
Throws:
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