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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.

Since:
JDK1.0

Constructor Summary
 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.
 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.
 

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, int off, int len)
Reads up to len bytes of data from this file into an array of bytes.
int  read(byte[] b)
Reads up to b.length bytes of data from this file into an array of bytes.
boolean  readBoolean()
Reads a boolean from this file.
byte  readByte()
Reads a signed 8-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.
void  readFully(byte[] b, int off, int len)
Reads exactly len bytes from this file into the byte array.
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 8-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(int b)
Writes the specified byte to this file.
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  writeBoolean(boolean v)
Writes a boolean to the file as a 1-byte value.
void  writeByte(int v)
Writes a byte to the file as a 1-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 2-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 8-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 4-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

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".
IOException - if an I/O error occurs.
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(java.lang.String)

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".
IOException - if an I/O error occurs.
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(java.lang.String)
Method Detail

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

read

public 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.

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.

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.

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.
Implements:
readFully in interface DataInput
Parameters:
b - the buffer into which the data is read.
Throws:
EOFException - if this file reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

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.
Implements:
readFully in interface DataInput
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.
IOException - if an I/O error occurs.

skipBytes

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.

Implements:
skipBytes in interface DataInput
Parameters:
n - the number of bytes to be skipped.
Returns:
the actual number of bytes skipped.
Throws:
IOException - if an I/O error occurs.

write

public void write(int b) throws IOException
Writes the specified byte to this file.
Implements:
write in interface DataOutput
Parameters:
b - the byte to be written.
Throws:
IOException - if an I/O error occurs.

write

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.
Implements:
write in interface DataOutput
Parameters:
b - the data.
Throws:
IOException - if an I/O error occurs.

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.
Implements:
write in interface DataOutput
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.

getFilePointer

public 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.

seek

public 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.

length

public long length() throws IOException
Returns the length of this file.
Returns:
the length of this file.
Throws:
IOException - if an I/O error occurs.

setLength

public 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 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.

Parameters:
newLength - The desired length of the file
Throws:
IOException - If an I/O error occurs

close

public 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.

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.
Implements:
readBoolean in interface DataInput
Returns:
the boolean value read.
Throws:
EOFException - if this file has reached the end.
IOException - if an I/O error occurs.

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:
     (byte)(b)
 

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

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

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.

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

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:
     (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.

Implements:
readShort in interface DataInput
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.
IOException - if an I/O error occurs.

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:
     (b1 << 8) | b2
 

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

Implements:
readUnsignedShort in interface DataInput
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.
IOException - if an I/O error occurs.

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:
     (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.

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

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.

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

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.

Implements:
readLong in interface DataInput
Returns:
the next eight bytes of this file, interpreted as a long.
Throws:
EOFException - if this file reaches the end before reading eight bytes.
IOException - if an I/O error occurs.

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.

Implements:
readFloat in interface DataInput
Returns:
the next four bytes of this file, interpreted as a float.
Throws:
EOFException - if this file reaches the end before reading four bytes.
IOException - if an I/O error occurs.
See Also:
readInt(), intBitsToFloat(int)

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.

Implements:
readDouble in interface DataInput
Returns:
the next eight bytes of this file, interpreted as a double.
Throws:
EOFException - if this file reaches the end before reading eight bytes.
IOException - if an I/O error occurs.
See Also:
readLong(), longBitsToDouble(long)

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 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.

Implements:
readLine in interface DataInput
Returns:
the next line of text from this file, or null if end of file is encountered before even one byte is read.
Throws:
IOException - if an I/O error occurs.

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.

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

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.
Implements:
writeBoolean in interface DataOutput
Parameters:
v - a boolean value to be written.
Throws:
IOException - if an I/O error occurs.

writeByte

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

writeShort

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

writeChar

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

writeInt

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

writeLong

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

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.
Implements:
writeFloat in interface DataOutput
Parameters:
v - a float value to be written.
Throws:
IOException - if an I/O error occurs.
See Also:
floatToIntBits(float)

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.
Implements:
writeDouble in interface DataOutput
Parameters:
v - a double value to be written.
Throws:
IOException - if an I/O error occurs.
See Also:
doubleToLongBits(double)

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.
Implements:
writeBytes in interface DataOutput
Parameters:
s - a string of bytes to be written.
Throws:
IOException - if an I/O error occurs.

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.
Implements:
writeChars in interface DataOutput
Parameters:
s - a String value to be written.
Throws:
IOException - if an I/O error occurs.
See Also:
writeChar(int)

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.

Implements:
writeUTF in interface DataOutput
Parameters:
str - a string to be written.
Throws:
IOException - if an I/O error occurs.

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