Instances of this class support both reading and writing to a
random access file. An application can modify the position in the
file at which the next read or write occurs.
This class provides a sense of security
by offering methods that allow specified mode accesses of
read-only or read-write to files.
close
public void close()
throws IOException
Closes this random access file and flushes any
unwritten data to the file.
After the file is closed further I/O operations may
throw IOException.
flush
public void flush()
throws IOException
Forces any buffered output bytes to be written out.
getFilePointer
public long getFilePointer()
throws IOException
Returns the current offset in this file.
- the offset from the beginning of the file, in bytes,
at which the next read or write occurs.
length
public long length()
throws IOException
Returns the length of this file.
read
public int read()
throws IOException
Reads a byte of data from this file.
- the next byte of data, or
-1
if the
end of the file is reached.
read
public int read(b[] )
throws IOException
Reads up to b.length
bytes of data from this file
into an array of bytes.
- 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.
read
public int read(b[] ,
int off,
int len)
throws IOException
Reads up to len
bytes of data from this file into
an array of bytes.
off
- the start offset of the data.len
- the maximum number of bytes read.
- 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.
readBoolean
public final boolean readBoolean()
throws IOException
Reads a boolean
from this file. This method reads a
single byte from the file. 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.
readByte
public final byte readByte()
throws IOException
Reads a signed 8-bit value from this file. This method reads a
byte from the file. 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.
- the next byte of this file as a signed 8-bit
byte
.
readChar
public final char readChar()
throws IOException
Reads a Unicode character from this file. This method reads two
bytes from the file. 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.
- the next two bytes of this file as a Unicode character.
readDouble
public final double readDouble()
throws IOException
Reads a
double
from this file. This method reads a
long
value 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.
- the next eight bytes of this file, interpreted as a
double
.
readLong()
, java.lang.Double.longBitsToDouble(long)
readFloat
public final float readFloat()
throws IOException
Reads a
float
from this file. This method reads an
int
value 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.
- the next four bytes of this file, interpreted as a
float
.
readInt()
, java.lang.Float.intBitsToFloat(int)
readFully
public final void readFully(b[] )
throws IOException
Reads b.length
bytes from this file into the byte
array.
readFully
public final void readFully(b[] ,
int off,
int len)
throws IOException
Reads exactly len
bytes from this file into
the byte array.
off
- the start offset of the data.len
- the number of bytes to read.
readInt
public final int readInt()
throws IOException
Reads a signed 32-bit integer from this file. This method reads 4
bytes from the file. 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.
- the next four bytes of this file, interpreted as an
int
.
readLine
public final String readLine()
throws IOException
Reads the next line of text from this file. This method
successively reads bytes from the file until it reaches the end of
a line of text.
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 input stream. The line-terminating
character(s), if any, are 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 stream is detected, or an exception is thrown.
- the next line of text from this file.
readLong
public final long readLong()
throws IOException
Reads a signed 64-bit integer from this file. This method reads eight
bytes from the file. 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.
- the next eight bytes of this file, interpreted as a
long
.
readShort
public final short readShort()
throws IOException
Reads a signed 16-bit number from this file. The method reads 2
bytes from this file. 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.
- the next two bytes of this file, interpreted as a signed
16-bit number.
readUTF
public final String readUTF()
throws IOException
Reads in a string from this file. The string has been encoded
using a modified UTF-8 format.
The first two bytes are read 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.
readUnsignedByte
public final int readUnsignedByte()
throws IOException
Reads an unsigned 8-bit number from this file. This method reads
a byte from this file and returns that byte.
This method blocks until the byte is read, the end of the stream
is detected, or an exception is thrown.
- the next byte of this file, interpreted as an unsigned
8-bit number.
readUnsignedShort
public final int readUnsignedShort()
throws IOException
Reads an unsigned 16-bit number from this file. This method reads
two bytes from the file. 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.
- the next two bytes of this file, interpreted as an unsigned
16-bit integer.
seek
public void seek(long pos)
throws IOException
Sets the offset from the beginning of this file at which
the next read or write occurs.
pos
- the absolute position.
skipBytes
public int skipBytes(int n)
throws IOException
Skips exactly
n
bytes of input.
n
- the number of bytes to be skipped.
- the number of bytes skipped, which is always
n
.
write
public void write(b[] )
throws IOException
Writes b.length
bytes from the specified byte array
starting at offset off
to this file.
write
public void write(b[] ,
int off,
int len)
throws IOException
Writes len
bytes from the specified byte array
starting at offset off
to this file.
off
- the start offset in the data.len
- the number of bytes to write.
write
public void write(int b)
throws IOException
Writes the specified byte to this file.
b
- the byte
to be written.
writeBoolean
public final void writeBoolean(boolean v)
throws IOException
Writes a boolean
to the file as a 1-byte value. The
value true
is written out as the value
(byte)1
; the value false
is written out
as the value (byte)0
.
v
- a boolean
value to be written.
writeByte
public final void writeByte(int v)
throws IOException
Writes a byte
to the file as a 1-byte value.
v
- a byte
value to be written.
writeBytes
public final void writeBytes(String s)
throws IOException
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.
s
- a string of bytes to be written.
writeChar
public final void writeChar(int v)
throws IOException
Writes a char
to the file as a 2-byte value, high
byte first.
v
- a char
value to be written.
writeChars
public final void writeChars(String s)
throws IOException
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.
s
- a String
value to be written.
writeDouble
public final void writeDouble(double v)
throws IOException
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
8-byte quantity, high byte first.
v
- a double
value to be written.
java.lang.Double.doubleToLongBits(double)
writeFloat
public final void writeFloat(float v)
throws IOException
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
4-byte quantity, high byte first.
v
- a float
value to be written.
java.lang.Float.floatToIntBits(float)
writeInt
public final void writeInt(int v)
throws IOException
Writes an int
to the file as four bytes, high byte first.
v
- an int
to be written.
writeLong
public final void writeLong(long v)
throws IOException
Writes a long
to the file as eight bytes, high byte first.
v
- a long
to be written.
writeShort
public final void writeShort(int v)
throws IOException
Writes a short
to the file as two bytes, high byte first.
v
- a short
to be written.
writeUTF
public final void writeUTF(String str)
throws IOException
Writes a string to the file using UTF-8 encoding in a
machine-independent manner.
First, two bytes are written to the file 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.