Class java.io.RandomAccessFile - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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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.

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

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

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

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

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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.

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

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.

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.

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.

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.

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.

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.

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

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

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.

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

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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