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Java Platform 1.2 |
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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.
| Constructor Summary | |
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. |
|
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. |
|
| Method Summary | |
void |
close()
Closes this random access file stream and releases any system resources associated with the stream. |
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 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. |
boolean |
readBoolean()
Reads a boolean from this file. |
byte |
readByte()
Reads a signed eight-bit value from this file. |
char |
readChar()
Reads a Unicode character from this file. |
double |
readDouble()
Reads a double from this file. |
float |
readFloat()
Reads a float from this file. |
void |
readFully(byte[] b)
Reads b.length bytes from this file into the byte
array, starting at the current file pointer. |
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. |
int |
readInt()
Reads a signed 32-bit integer from this file. |
String |
readLine()
Reads the next line of text from this file. |
long |
readLong()
Reads a signed 64-bit integer from this file. |
short |
readShort()
Reads a signed 16-bit number from this file. |
int |
readUnsignedByte()
Reads an unsigned eight-bit number from this file. |
int |
readUnsignedShort()
Reads an unsigned 16-bit number from this file. |
String |
readUTF()
Reads in a string from this file. |
void |
seek(long pos)
Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs. |
void |
setLength(long newLength)
Sets the length of this file. |
int |
skipBytes(int n)
Attempts to skip over n bytes of input discarding the
skipped bytes. |
void |
write(byte[] b)
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 |
write(int b)
Writes the specified byte to this file. |
void |
writeBoolean(boolean v)
Writes a boolean to the file as a one-byte value. |
void |
writeByte(int v)
Writes a byte to the file as a one-byte value. |
void |
writeBytes(String s)
Writes the string to the file as a sequence of bytes. |
void |
writeChar(int v)
Writes a char to the file as a two-byte value, high
byte first. |
void |
writeChars(String s)
Writes a string to the file as a sequence of characters. |
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. |
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. |
void |
writeInt(int v)
Writes an int to the file as four bytes, high byte first. |
void |
writeLong(long v)
Writes a long to the file as eight bytes, high byte first. |
void |
writeShort(int v)
Writes a short to the file as two bytes, high byte first. |
void |
writeUTF(String str)
Writes a string to the file using UTF-8 encoding in a machine-independent manner. |
| Methods inherited from class java.lang.Object |
clone,
equals,
finalize,
getClass,
hashCode,
notify,
notifyAll,
toString,
wait,
wait,
wait |
| Constructor Detail |
public RandomAccessFile(String name,
String mode)
throws FileNotFoundException
FileDescriptor object is created to represent the
connection to the file.
The mode argument must either be equal to "r" or
"rw", indicating that the file is to be opened for
input only or for both input and output, respectively. The
write methods on this object will always throw an
IOException if the file is opened with a mode of
"r". If the mode is "rw" and the
file does not exist, then an attempt is made to create it.
An IOException is thrown if the name argument
refers to a directory.
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 is "rw", 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."r" or to "rw".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.SecurityException,
SecurityManager.checkRead(java.lang.String),
SecurityManager.checkWrite(java.lang.String)
public RandomAccessFile(File file,
String mode)
throws IOException
File argument.
A new FileDescriptor object is created to represent
this file connection.
The mode argument must either be equal to "r" or
"rw", indicating that the file is to be opened for
input only or for both input and output, respectively. The
write methods on this object will always throw an
IOException if the file is opened with a mode of
"r". If the mode is "rw" and the
file does not exist, then an attempt is made to create it.
An IOException is thrown if the file argument
refers to a directory.
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 is "rw", 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."r" or to "rw".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.File.getPath(),
SecurityManager.checkRead(java.lang.String),
SecurityManager.checkWrite(java.lang.String)| Method Detail |
public final FileDescriptor getFD()
throws IOException
FileDescriptor
public int read()
throws IOException
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.
public int read(byte[] b,
int off,
int len)
throws IOException
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 the 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 of the data.len - the maximum number of bytes read.-1 if there is no more data because the end of
the file has been reached.
public int read(byte[] b)
throws IOException
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 the 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.
public final void readFully(byte[] b)
throws IOException
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.b - the buffer into which the data is read.
public final void readFully(byte[] b,
int off,
int len)
throws IOException
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.b - the buffer into which the data is read.off - the start offset of the data.len - the number of bytes to read.
public int skipBytes(int n)
throws IOException
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.
n - the number of bytes to be skipped.
public void write(int b)
throws IOException
b - the byte to be written.
public void write(byte[] b)
throws IOException
b.length bytes from the specified byte array
to this file, starting at the current file pointer.b - the data.
public void write(byte[] b,
int off,
int len)
throws IOException
len bytes from the specified byte array
starting at offset off to this file.b - the data.off - the start offset in the data.len - the number of bytes to write.
public long getFilePointer()
throws IOException
public void seek(long pos)
throws IOException
pos - the offset position, measured in bytes from the
beginning of the file, at which to set the file
pointer.pos is less than
0 or if an I/O error occurs.
public long length()
throws IOException
public void setLength(long newLength)
throws IOException
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
then 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
public void close()
throws IOException
public final boolean readBoolean()
throws IOException
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.boolean value read.
public final byte readByte()
throws IOException
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.
byte.
public final int readUnsignedByte()
throws IOException
This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.
public final short readShort()
throws IOException
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.
public final int readUnsignedShort()
throws IOException
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.
public final char readChar()
throws IOException
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.
public final int readInt()
throws IOException
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.
int.
public final long readLong()
throws IOException
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.
long.
public final float readFloat()
throws IOException
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.
float.readInt(),
Float.intBitsToFloat(int)
public final double readDouble()
throws IOException
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.
double.readLong(),
Double.longBitsToDouble(long)
public final String readLine()
throws IOException
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.
public final String readUTF()
throws IOException
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 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.
readUnsignedShort()
public final void writeBoolean(boolean v)
throws IOException
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.v - a boolean value to be written.
public final void writeByte(int v)
throws IOException
byte to the file as a one-byte value. The
write starts at the current position of the file pointer.v - a byte value to be written.
public final void writeShort(int v)
throws IOException
short to the file as two bytes, high byte first.
The write starts at the current position of the file pointer.v - a short to be written.
public final void writeChar(int v)
throws IOException
char to the file as a two-byte value, high
byte first. The write starts at the current position of the
file pointer.v - a char value to be written.
public final void writeInt(int v)
throws IOException
int to the file as four bytes, high byte first.
The write starts at the current position of the file pointer.v - an int to be written.
public final void writeLong(long v)
throws IOException
long to the file as eight bytes, high byte first.
The write starts at the current position of the file pointer.v - a long to be written.
public final void writeFloat(float v)
throws IOException
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.v - a float value to be written.Float.floatToIntBits(float)
public final void writeDouble(double v)
throws IOException
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.v - a double value to be written.Double.doubleToLongBits(double)
public final void writeBytes(String s)
throws IOException
s - a string of bytes to be written.
public final void writeChars(String s)
throws IOException
writeChar method. The write starts at the current
position of the file pointer.s - a String value to be written.writeChar(int)
public final void writeUTF(String str)
throws IOException
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 UTF-8 encoding
for each character.
str - a string to be written.
|
Java Platform 1.2 |
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| SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD | |||||||||