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
;
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
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.
| Method from java.io.RandomAccessFile Detail: |
|---|
 public void close() throws IOException {
synchronized (closeLock) {
if (closed) {
return;
}
closed = true;
}
if (channel != null) {
/*
* Decrement FD use count associated with the channel. The FD use
* count is incremented whenever a new channel is obtained from
* this stream.
*/
fd.decrementAndGetUseCount();
channel.close();
}
/*
* Decrement FD use count associated with this stream.
* The count got incremented by FileDescriptor during its construction.
*/
fd.decrementAndGetUseCount();
close0();
}
|
public final FileChannel getChannel() {
synchronized (this) {
if (channel == null) {
channel = FileChannelImpl.open(fd, true, rw, this);
/*
* FileDescriptor could be shared by FileInputStream or
* FileOutputStream.
* Ensure that FD is GC'ed only when all the streams/channels
* are done using it.
* Increment fd's use count. Invoking the channel's close()
* method will result in decrementing the use count set for
* the channel.
*/
fd.incrementAndGetUseCount();
}
return channel;
}
} Returns the unique FileChannel
object associated with this file.
The position |
public final FileDescriptor getFD() throws IOException {
if (fd != null) return fd;
throw new IOException();
} Returns the opaque file descriptor object associated with this
stream. |
 public native long getFilePointer() throws IOException
Returns the current offset in this file. |
public native long length() throws IOException Returns the length of this file. |
public native int read() throws IOException 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. |
public int read(byte[] b) throws IOException {
return readBytes(b, 0, b.length);
} 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. |
public int read(byte[] b,
int off,
int len) throws IOException {
return readBytes(b, off, 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. |
public final boolean readBoolean() throws IOException {
int ch = this.read();
if (ch < 0)
throw new EOFException();
return (ch != 0);
} 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. |
public final byte readByte() throws IOException {
int ch = this.read();
if (ch < 0)
throw new EOFException();
return (byte)(ch);
} 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. |
public final char readChar() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (char)((ch1 < < 8) + (ch2 < < 0));
} 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. |
public final double readDouble() throws IOException {
return Double.longBitsToDouble(readLong());
} 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. |
public final float readFloat() throws IOException {
return Float.intBitsToFloat(readInt());
} 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. |
public final void readFully(byte[] b) throws IOException {
readFully(b, 0, b.length);
} 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. |
public final void readFully(byte[] b,
int off,
int len) throws IOException {
int n = 0;
do {
int count = this.read(b, off + n, len - n);
if (count < 0)
throw new EOFException();
n += count;
} while (n < 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. |
public final int readInt() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
int ch3 = this.read();
int ch4 = this.read();
if ((ch1 | ch2 | ch3 | ch4) < 0)
throw new EOFException();
return ((ch1 < < 24) + (ch2 < < 16) + (ch3 < < 8) + (ch4 < < 0));
} 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. |
public final String readLine() throws IOException {
StringBuffer input = new StringBuffer();
int c = -1;
boolean eol = false;
while (!eol) {
switch (c = read()) {
case -1:
case '\n':
eol = true;
break;
case '\r':
eol = true;
long cur = getFilePointer();
if ((read()) != '\n') {
seek(cur);
}
break;
default:
input.append((char)c);
break;
}
}
if ((c == -1) && (input.length() == 0)) {
return null;
}
return input.toString();
} 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. |
public final long readLong() throws IOException {
return ((long)(readInt()) < < 32) + (readInt() & 0xFFFFFFFFL);
} 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. |
public final short readShort() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (short)((ch1 < < 8) + (ch2 < < 0));
} 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. |
public final String readUTF() throws IOException {
return DataInputStream.readUTF(this);
} 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. |
public final int readUnsignedByte() throws IOException {
int ch = this.read();
if (ch < 0)
throw new EOFException();
return ch;
} 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. |
public final int readUnsignedShort() throws IOException {
int ch1 = this.read();
int ch2 = this.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (ch1 < < 8) + (ch2 < < 0);
} 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. |
public native void seek(long pos) throws IOException 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. |
public native void setLength(long newLength) throws IOException 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. |
public int skipBytes(int n) throws IOException {
long pos;
long len;
long newpos;
if (n < = 0) {
return 0;
}
pos = getFilePointer();
len = length();
newpos = pos + n;
if (newpos > len) {
newpos = len;
}
seek(newpos);
/* return the actual number of bytes skipped */
return (int) (newpos - pos);
} 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. |
public native void write(int b) throws IOException Writes the specified byte to this file. The write starts at
the current file pointer. |
public void write(byte[] b) throws IOException {
writeBytes(b, 0, b.length);
} Writes b.length bytes from the specified byte array
to this file, starting at the current file pointer. |
public void write(byte[] b,
int off,
int len) throws IOException {
writeBytes(b, off, len);
} Writes len bytes from the specified byte array
starting at offset off to this file. |
public final void writeBoolean(boolean v) throws IOException {
write(v ? 1 : 0);
//written++;
} 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. |
public final void writeByte(int v) throws IOException {
write(v);
//written++;
} Writes a byte to the file as a one-byte value. The
write starts at the current position of the file pointer. |
public final void writeBytes(String s) throws IOException {
int len = s.length();
byte[] b = new byte[len];
s.getBytes(0, len, b, 0);
writeBytes(b, 0, len);
} 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. |
public final void writeChar(int v) throws IOException {
write((v > > > 8) & 0xFF);
write((v > > > 0) & 0xFF);
//written += 2;
} 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. |
public final void writeChars(String s) throws IOException {
int clen = s.length();
int blen = 2*clen;
byte[] b = new byte[blen];
char[] c = new char[clen];
s.getChars(0, clen, c, 0);
for (int i = 0, j = 0; i < clen; i++) {
b[j++] = (byte)(c[i] > > > 8);
b[j++] = (byte)(c[i] > > > 0);
}
writeBytes(b, 0, blen);
} 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. |
public final void writeDouble(double v) throws IOException {
writeLong(Double.doubleToLongBits(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. |
public final void writeFloat(float v) throws IOException {
writeInt(Float.floatToIntBits(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. |
public final void writeInt(int v) throws IOException {
write((v > > > 24) & 0xFF);
write((v > > > 16) & 0xFF);
write((v > > > 8) & 0xFF);
write((v > > > 0) & 0xFF);
//written += 4;
} Writes an int to the file as four bytes, high byte first.
The write starts at the current position of the file pointer. |
public final void writeLong(long v) throws IOException {
write((int)(v > > > 56) & 0xFF);
write((int)(v > > > 48) & 0xFF);
write((int)(v > > > 40) & 0xFF);
write((int)(v > > > 32) & 0xFF);
write((int)(v > > > 24) & 0xFF);
write((int)(v > > > 16) & 0xFF);
write((int)(v > > > 8) & 0xFF);
write((int)(v > > > 0) & 0xFF);
//written += 8;
} Writes a long to the file as eight bytes, high byte first.
The write starts at the current position of the file pointer. |
public final void writeShort(int v) throws IOException {
write((v > > > 8) & 0xFF);
write((v > > > 0) & 0xFF);
//written += 2;
} Writes a short to the file as two bytes, high byte first.
The write starts at the current position of the file pointer. |
public final void writeUTF(String str) throws IOException {
DataOutputStream.writeUTF(str, this);
} 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. |
java.io.RandomAccessFile