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Class java.io.RandomAccessFile

java.lang.Object
   |
   +----java.io.RandomAccessFile

public class RandomAccessFile
extends Object
implements DataOutput, DataInput
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.


Constructor Index

 o RandomAccessFile(File, String)
Creates a random access file stream to read from, and optionally to write to, the file specified by the File argument.
 o RandomAccessFile(String, String)
Creates a random access file stream to read from, and optionally to write to, a file with the specified name.

Method Index

 o close()
Closes this random access file stream and releases any system resources associated with the stream.
 o getFD()
Returns the opaque file descriptor object associated with this stream.
 o getFilePointer()
Returns the current offset in this file.
 o length()
Returns the length of this file.
 o read()
Reads a byte of data from this file.
 o read(byte[])
Reads up to b.length bytes of data from this file into an array of bytes.
 o read(byte[], int, int)
Reads up to len bytes of data from this file into an array of bytes.
 o readBoolean()
Reads a boolean from this file.
 o readByte()
Reads a signed 8-bit value from this file.
 o readChar()
Reads a Unicode character from this file.
 o readDouble()
Reads a double from this file.
 o readFloat()
Reads a float from this file.
 o readFully(byte[])
Reads b.length bytes from this file into the byte array.
 o readFully(byte[], int, int)
Reads exactly len bytes from this file into the byte array.
 o readInt()
Reads a signed 32-bit integer from this file.
 o readLine()
Reads the next line of text from this file.
 o readLong()
Reads a signed 64-bit integer from this file.
 o readShort()
Reads a signed 16-bit number from this file.
 o readUnsignedByte()
Reads an unsigned 8-bit number from this file.
 o readUnsignedShort()
Reads an unsigned 16-bit number from this file.
 o readUTF()
Reads in a string from this file.
 o seek(long)
Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.
 o skipBytes(int)
Skips exactly n bytes of input.
 o write(byte[])
Writes b.length bytes from the specified byte array starting at offset off to this file.
 o write(byte[], int, int)
Writes len bytes from the specified byte array starting at offset off to this file.
 o write(int)
Writes the specified byte to this file.
 o writeBoolean(boolean)
Writes a boolean to the file as a 1-byte value.
 o writeByte(int)
Writes a byte to the file as a 1-byte value.
 o writeBytes(String)
Writes the string to the file as a sequence of bytes.
 o writeChar(int)
Writes a char to the file as a 2-byte value, high byte first.
 o writeChars(String)
Writes a string to the file as a sequence of characters.
 o writeDouble(double)
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.
 o writeFloat(float)
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.
 o writeInt(int)
Writes an int to the file as four bytes, high byte first.
 o writeLong(long)
Writes a long to the file as eight bytes, high byte first.
 o writeShort(int)
Writes a short to the file as two bytes, high byte first.
 o writeUTF(String)
Writes a string to the file using UTF-8 encoding in a machine-independent manner.

Constructors

 o RandomAccessFile
 public RandomAccessFile(String name,
                         String mode) throws IOException
Creates a random access file stream to read from, and optionally to write to, a file with the specified name.

The mode argument must either be equal to "r" or "rw", indicating either to open the file for input or for both input and output.

Parameters:
name - the system-dependent filename.
mode - the access mode.
Throws: IllegalArgumentException
if the mode argument is not equal to "r" or to "rw".
Throws: IOException
if an I/O error occurs.
Throws: SecurityException
if a security manager exists, its checkRead method is called with the name argument to see if the application is allowed read access to the file. If the mode argument is equal to "rw", its checkWrite method also is called with the name argument to see if the application is allowed write access to the file. Either of these may result in a security exception.
See Also:
SecurityException, checkRead
 o RandomAccessFile
 public RandomAccessFile(File file,
                         String mode) throws IOException
Creates a random access file stream to read from, and optionally to write to, the file specified by the File argument.

The mode argument must either be equal to "r" or to "rw", indicating either to open the file for input, or for both input and output, respectively.

Parameters:
file - the file object.
mode - the access mode.
Throws: IllegalArgumentException
if the mode argument is not equal to "r" or to "rw".
Throws: IOException
if an I/O error occurs.
Throws: SecurityException
if a security manager exists, its checkRead method is called with the pathname of the File argument to see if the application is allowed read access to the file. If the mode argument is equal to "rw", its checkWrite method also is called with the pathname to see if the application is allowed write access to the file.
See Also:
getPath, checkRead

Methods

 o getFD
 public final FileDescriptor getFD() throws IOException
Returns the opaque file descriptor object associated with this stream.

Returns:
the file descriptor object associated with this stream.
Throws: IOException
if an I/O error occurs.
See Also:
FileDescriptor
 o read
 public native int read() throws IOException
Reads a byte of data from this file. This method blocks if no input is yet available.

Returns:
the next byte of data, or -1 if the end of the file is reached.
Throws: IOException
if an I/O error occurs.
 o read
 public int read(byte b[],
                 int off,
                 int len) throws IOException
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.

Parameters:
b - the buffer into which the data is read.
off - the start offset of the data.
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 an I/O error occurs.
 o read
 public int read(byte b[]) throws IOException
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.

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 an I/O error occurs.
 o readFully
 public final void readFully(byte b[]) throws IOException
Reads b.length bytes from this file into the byte array. This method reads repeatedly from the file until all the bytes are read. This method blocks until all the bytes are read, the end of the stream is detected, or an exception is thrown.

Parameters:
b - the buffer into which the data is read.
Throws: EOFException
if this file reaches the end before reading all the bytes.
Throws: IOException
if an I/O error occurs.
 o readFully
 public final void readFully(byte b[],
                             int off,
                             int len) throws IOException
Reads exactly len bytes from this file into the byte array. This method reads repeatedly from the file until all the bytes are read. This method blocks until all the bytes are read, the end of the stream is detected, or an exception is thrown.

Parameters:
b - the buffer into which the data is read.
off - the start offset of the data.
len - the number of bytes to read.
Throws: EOFException
if this file reaches the end before reading all the bytes.
Throws: IOException
if an I/O error occurs.
 o skipBytes
 public int skipBytes(int n) throws IOException
Skips exactly n bytes of input.

This method blocks until all the bytes are skipped, the end of the stream is detected, or an exception is thrown.

Parameters:
n - the number of bytes to be skipped.
Returns:
the number of bytes skipped, which is always n.
Throws: EOFException
if this file reaches the end before skipping all the bytes.
Throws: IOException
if an I/O error occurs.
 o write
 public native void write(int b) throws IOException
Writes the specified byte to this file.

Parameters:
b - the byte to be written.
Throws: IOException
if an I/O error occurs.
 o write
 public void write(byte b[]) throws IOException
Writes b.length bytes from the specified byte array starting at offset off to this file.

Parameters:
b - the data.
Throws: IOException
if an I/O error occurs.
 o write
 public void write(byte b[],
                   int off,
                   int len) throws IOException
Writes len bytes from the specified byte array starting at offset off to this file.

Parameters:
b - the data.
off - the start offset in the data.
len - the number of bytes to write.
Throws: IOException
if an I/O error occurs.
 o getFilePointer
 public native long getFilePointer() throws IOException
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: IOException
if an I/O error occurs.
 o seek
 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.

Parameters:
pos - the offset position, measured in bytes from the beginning of the file, at which to set the file pointer.
Throws: IOException
if an I/O error occurs.
 o length
 public native long length() throws IOException
Returns the length of this file.

Returns:
the length of this file.
Throws: IOException
if an I/O error occurs.
 o close
 public native void close() throws IOException
Closes this random access file stream and releases any system resources associated with the stream.

Throws: IOException
if an I/O error occurs.
 o 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.

Returns:
the boolean value read.
Throws: EOFException
if this file has reached the end.
Throws: IOException
if an I/O error occurs.
 o 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.

Returns:
the next byte of this file as a signed 8-bit byte.
Throws: EOFException
if this file has reached the end.
Throws: IOException
if an I/O error occurs.
 o 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.

Returns:
the next byte of this file, interpreted as an unsigned 8-bit number.
Throws: EOFException
if this file has reached the end.
Throws: IOException
if an I/O error occurs.
 o 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.

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.
Throws: IOException
if an I/O error occurs.
 o 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.

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.
Throws: IOException
if an I/O error occurs.
 o 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.

Returns:
the next two bytes of this file as a Unicode character.
Throws: EOFException
if this file reaches the end before reading two bytes.
Throws: IOException
if an I/O error occurs.
 o 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:

This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next four bytes of this file, interpreted as an int.
Throws: EOFException
if this file reaches the end before reading four bytes.
Throws: IOException
if an I/O error occurs.
 o 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:

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:
the next eight bytes of this file, interpreted as a long.
Throws: EOFException
if this file reaches the end before reading eight bytes.
Throws: IOException
if an I/O error occurs.
 o 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.

Returns:
the next four bytes of this file, interpreted as a float.
Throws: EOFException
if this file reaches the end before reading four bytes.
Throws: IOException
if an I/O error occurs.
See Also:
readInt, intBitsToFloat
 o 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.

Returns:
the next eight bytes of this file, interpreted as a double.
Throws: EOFException
if this file reaches the end before reading eight bytes.
Throws: IOException
if an I/O error occurs.
See Also:
readLong, longBitsToDouble
 o 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.

Returns:
the next line of text from this file.
Throws: IOException
if an I/O error occurs.
 o 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.

Returns:
a Unicode string.
Throws: EOFException
if this file reaches the end before reading all the bytes.
Throws: IOException
if an I/O error occurs.
Throws: UTFDataFormatException
if the bytes do not represent valid UTF-8 encoding of a Unicode string.
See Also:
readUnsignedShort
 o 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.

Parameters:
v - a boolean value to be written.
Throws: IOException
if an I/O error occurs.
 o writeByte
 public final void writeByte(int v) throws IOException
Writes a byte to the file as a 1-byte value.

Parameters:
v - a byte value to be written.
Throws: IOException
if an I/O error occurs.
 o writeShort
 public final void writeShort(int v) throws IOException
Writes a short to the file as two bytes, high byte first.

Parameters:
v - a short to be written.
Throws: IOException
if an I/O error occurs.
 o writeChar
 public final void writeChar(int v) throws IOException
Writes a char to the file as a 2-byte value, high byte first.

Parameters:
v - a char value to be written.
Throws: IOException
if an I/O error occurs.
 o writeInt
 public final void writeInt(int v) throws IOException
Writes an int to the file as four bytes, high byte first.

Parameters:
v - an int to be written.
Throws: IOException
if an I/O error occurs.
 o writeLong
 public final void writeLong(long v) throws IOException
Writes a long to the file as eight bytes, high byte first.

Parameters:
v - a long to be written.
Throws: IOException
if an I/O error occurs.
 o 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.

Parameters:
v - a float value to be written.
Throws: IOException
if an I/O error occurs.
See Also:
floatToIntBits
 o 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.

Parameters:
v - a double value to be written.
Throws: IOException
if an I/O error occurs.
See Also:
doubleToLongBits
 o 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.

Parameters:
s - a string of bytes to be written.
Throws: IOException
if an I/O error occurs.
 o 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.

Parameters:
s - a String value to be written.
Throws: IOException
if an I/O error occurs.
See Also:
writeChar
 o 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.

Parameters:
str - a string to be written.
Throws: IOException
if an I/O error occurs.

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