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java.io
public class: RandomAccessFile [javadoc | source]
java.lang.Object
   java.io.RandomAccessFile

All Implemented Interfaces:
    DataOutput, Closeable, DataInput

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:
 public RandomAccessFile(String name,
    String mode) throws FileNotFoundException 
    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
    mode - the access mode
    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
    Also see:
    java.lang.SecurityException
    java.lang.SecurityManager#checkRead(java.lang.String)
    java.lang.SecurityManager#checkWrite(java.lang.String)
    exception: IllegalArgumentException - if the mode argument is not equal to one of "r", "rw", "rws", or "rwd"
    exception: 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
    exception: 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
    revised: 1.4 -
    spec: JSR-51 -
 public RandomAccessFile(File file,
    String mode) throws FileNotFoundException 
    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
    Also see:
    java.lang.SecurityManager#checkRead(java.lang.String)
    java.lang.SecurityManager#checkWrite(java.lang.String)
    java.nio.channels.FileChannel#force(boolean)
    exception: IllegalArgumentException - if the mode argument is not equal to one of "r", "rw", "rws", or "rwd"
    exception: 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
    exception: 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
    revised: 1.4 -
    spec: JSR-51 -
Method from java.io.RandomAccessFile Summary:
close,   getChannel,   getFD,   getFilePointer,   length,   read,   read,   read,   readBoolean,   readByte,   readChar,   readDouble,   readFloat,   readFully,   readFully,   readInt,   readLine,   readLong,   readShort,   readUTF,   readUnsignedByte,   readUnsignedShort,   seek,   setLength,   skipBytes,   write,   write,   write,   writeBoolean,   writeByte,   writeBytes,   writeChar,   writeChars,   writeDouble,   writeFloat,   writeInt,   writeLong,   writeShort,   writeUTF
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.io.RandomAccessFile Detail:
 public  void close() throws IOException 
    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.

 public final FileChannel getChannel() 
    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.

 public final FileDescriptor getFD() throws 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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    Writes len bytes from the specified byte array starting at offset off to this file.
 public final  void writeBoolean(boolean v) throws IOException 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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 
    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.