Class: java.io.RandomAccessFile
- public class RandomAccessFile
- implements DataOutput, DataInput, Closeable
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.
Methods
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RandomAccessFiletop
Creates a random access file stream to read from, and optionally to write to, the file specified by the java.io.File argument. A new java.io.FileDescriptor object is created to represent this file connection.The mode argument specifies the access mode in which the file is to be opened. The permitted values and their meanings are:
The "rws" and "rwd" modes work much like the force(boolean) method of the java.nio.channels.FileChannel class, passing arguments of true and false, respectively, except that they always apply to every I/O operation and are therefore often more efficient. If the file resides on a local storage device then when an invocation of a method of this class returns it is guaranteed that all changes made to the file by that invocation will have been written to that device. This is useful for ensuring that critical information is not lost in the event of a system crash. If the file does not reside on a local device then no such guarantee is made.Value
Meaning
"r" Open for reading only. Invoking any of the write methods of the resulting object will cause an java.io.IOException to be thrown. "rw" Open for reading and writing. If the file does not already exist then an attempt will be made to create it. "rws" Open for reading and writing, as with "rw", and also require that every update to the file's content or metadata be written synchronously to the underlying storage device. "rwd" Open for reading and writing, as with "rw", and also require that every update to the file's content be written synchronously to the underlying storage device. The "rwd" mode can be used to reduce the number of I/O operations performed. Using "rwd" only requires updates to the file's content to be written to storage; using "rws" requires updates to both the file's content and its metadata to be written, which generally requires at least one more low-level I/O operation.
If there is a security manager, its
checkReadmethod is called with the pathname of thefileargument as its argument to see if read access to the file is allowed. If the mode allows writing, the security manager'scheckWritemethod is also called with the path argument to see if write access to the file is allowed. -
RandomAccessFiletop
Creates a random access file stream to read from, and optionally to write to, a file with the specified name. A new java.io.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
checkReadmethod is called with thenameargument as its argument to see if read access to the file is allowed. If the mode allows writing, the security manager'scheckWritemethod is also called with thenameargument as its argument to see if write access to the file is allowed. -
closetop
public void close() throws IOExceptionCloses 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.
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getChanneltop
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. -
getFDtop
public final FileDescriptor getFD() throws IOExceptionReturns the opaque file descriptor object associated with this stream. -
getFilePointertop
public native long getFilePointer() throws IOExceptionReturns the current offset in this file. -
lengthtop
public native long length() throws IOExceptionReturns the length of this file. -
readtop
public native int read() throws IOExceptionReads 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
RandomAccessFileis not a subclass ofInputStream, this method behaves in exactly the same way as the java.io.InputStream.read() method ofInputStream. -
readtop
public int read(byte[] b) throws IOExceptionReads up tob.lengthbytes of data from this file into an array of bytes. This method blocks until at least one byte of input is available.Although
RandomAccessFileis not a subclass ofInputStream, this method behaves in exactly the same way as the java.io.InputStream.read(byte[]) method ofInputStream. -
readtop
public int read(byte[] b, int off, int len) throws IOExceptionReads up tolenbytes of data from this file into an array of bytes. This method blocks until at least one byte of input is available.Although
RandomAccessFileis not a subclass ofInputStream, this method behaves in exactly the same way as the java.io.InputStream.read(byte[], int, int) method ofInputStream. -
readBooleantop
public final boolean readBoolean() throws IOExceptionReads abooleanfrom this file. This method reads a single byte from the file, starting at the current file pointer. A value of0representsfalse. Any other value representstrue. This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.- Specified by:
- readBoolean from DataInput
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readBytetop
public final byte readByte() throws IOExceptionReads 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 isb, where0 <= 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.
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readChartop
public final char readChar() throws IOExceptionReads 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, areb1andb2, where0 <= 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.
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readDoubletop
public final double readDouble() throws IOExceptionReads adoublefrom this file. This method reads alongvalue, starting at the current file pointer, as if by thereadLongmethod and then converts thatlongto adoubleusing thelongBitsToDoublemethod in classDouble.This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
- readDouble from DataInput
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readFloattop
public final float readFloat() throws IOExceptionReads afloatfrom this file. This method reads anintvalue, starting at the current file pointer, as if by thereadIntmethod and then converts thatintto afloatusing theintBitsToFloatmethod in classFloat.This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
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readFullytop
public final void readFully(byte[] b) throws IOExceptionReadsb.lengthbytes 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. -
readFullytop
public final void readFully(byte[] b, int off, int len) throws IOExceptionReads exactlylenbytes 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. -
readInttop
public final int readInt() throws IOExceptionReads 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, areb1,b2,b3, andb4, where0 <= b1, b2, b3, b4 <= 255, then the result is equal to:(b1 << 24) | (b2 << 16) + (b3 << 8) + b4This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.
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readLinetop
public final String readLine() throws IOExceptionReads 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.
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readLongtop
public final long readLong() throws IOExceptionReads 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, areb1,b2,b3,b4,b5,b6,b7, andb8,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) + b8This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.
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readShorttop
public final short readShort() throws IOExceptionReads 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, areb1andb2, where each of the two values is between0and255, 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.
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readUTFtop
public final String readUTF() throws IOExceptionReads 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.
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readUnsignedBytetop
public final int readUnsignedByte() throws IOExceptionReads 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.
- Specified by:
- readUnsignedByte from DataInput
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readUnsignedShorttop
public final int readUnsignedShort() throws IOExceptionReads 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, areb1andb2, where0 <= b1, b2 <= 255, then the result is equal to:(b1 << 8) | b2This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.
- Specified by:
- readUnsignedShort from DataInput
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seektop
public native void seek(long pos) throws IOExceptionSets 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. -
setLengthtop
public native void setLength(long newLength) throws IOExceptionSets the length of this file.If the present length of the file as returned by the
lengthmethod is greater than thenewLengthargument then the file will be truncated. In this case, if the file offset as returned by thegetFilePointermethod is greater thannewLengththen after this method returns the offset will be equal tonewLength.If the present length of the file as returned by the
lengthmethod is smaller than thenewLengthargument then the file will be extended. In this case, the contents of the extended portion of the file are not defined. -
skipBytestop
public int skipBytes(int n) throws IOExceptionAttempts to skip overnbytes 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
nbytes have been skipped is only one possibility. This method never throws anEOFException. The actual number of bytes skipped is returned. Ifnis negative, no bytes are skipped. -
writetop
public native void write(int b) throws IOExceptionWrites the specified byte to this file. The write starts at the current file pointer.- Specified by:
- write from DataOutput
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writetop
public void write(byte[] b) throws IOExceptionWritesb.lengthbytes from the specified byte array to this file, starting at the current file pointer.- Specified by:
- write from DataOutput
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writetop
public void write(byte[] b, int off, int len) throws IOExceptionWriteslenbytes from the specified byte array starting at offsetoffto this file.- Specified by:
- write from DataOutput
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writeBooleantop
public final void writeBoolean(boolean v) throws IOExceptionWrites abooleanto the file as a one-byte value. The valuetrueis written out as the value(byte)1; the valuefalseis written out as the value(byte)0. The write starts at the current position of the file pointer.- Specified by:
- writeBoolean from DataOutput
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writeBytetop
public final void writeByte(int v) throws IOExceptionWrites abyteto the file as a one-byte value. The write starts at the current position of the file pointer.- Specified by:
- writeByte from DataOutput
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writeBytestop
public final void writeBytes(String s) throws IOExceptionWrites 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.- Specified by:
- writeBytes from DataOutput
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writeChartop
public final void writeChar(int v) throws IOExceptionWrites acharto the file as a two-byte value, high byte first. The write starts at the current position of the file pointer.- Specified by:
- writeChar from DataOutput
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writeCharstop
public final void writeChars(String s) throws IOExceptionWrites a string to the file as a sequence of characters. Each character is written to the data output stream as if by thewriteCharmethod. The write starts at the current position of the file pointer.- Specified by:
- writeChars from DataOutput
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writeDoubletop
public final void writeDouble(double v) throws IOExceptionConverts the double argument to alongusing thedoubleToLongBitsmethod in classDouble, and then writes thatlongvalue to the file as an eight-byte quantity, high byte first. The write starts at the current position of the file pointer.- Specified by:
- writeDouble from DataOutput
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writeFloattop
public final void writeFloat(float v) throws IOExceptionConverts the float argument to anintusing thefloatToIntBitsmethod in classFloat, and then writes thatintvalue to the file as a four-byte quantity, high byte first. The write starts at the current position of the file pointer.- Specified by:
- writeFloat from DataOutput
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writeInttop
public final void writeInt(int v) throws IOExceptionWrites anintto the file as four bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
- writeInt from DataOutput
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writeLongtop
public final void writeLong(long v) throws IOExceptionWrites alongto the file as eight bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
- writeLong from DataOutput
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writeShorttop
public final void writeShort(int v) throws IOExceptionWrites ashortto the file as two bytes, high byte first. The write starts at the current position of the file pointer.- Specified by:
- writeShort from DataOutput
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writeUTFtop
public final void writeUTF(String str) throws IOExceptionWrites 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
writeShortmethod 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.- Specified by:
- writeUTF from DataOutput
