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Summary: Nested | Field | Method | Constr | Detail: Nested | Field | Method | Constr |
java.lang.Object
java.io.RandomAccessFile
DataInput
and DataOutput
interfaces to allow
the reading and writing of Java primitives.
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FileChannel |
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Methods inherited from class java.lang.Object | |
clone , equals , extends Object> getClass , finalize , hashCode , notify , notifyAll , toString , wait , wait , wait |
public RandomAccessFile(File file, String mode) throws FileNotFoundException
This method initializes a new instance ofRandomAccessFile
to read from the specifiedFile
object with the specified access mode. The access mode is either "r" for read only access or "rw" for read-write access. Note that aSecurityManager
check is made prior to opening the file to determine whether or not this file is allowed to be read or written.
- Parameters:
file
- TheFile
object to read and/or write.mode
- "r" for read only or "rw" for read-write access to the file
- Throws:
IllegalArgumentException
- Ifmode
has an illegal valueSecurityException
- If the requested access to the file is not allowedFileNotFoundException
- If the file is a directory, or any other error occurs
public RandomAccessFile(String fileName, String mode) throws FileNotFoundException
This method initializes a new instance ofRandomAccessFile
to read from the specified file name with the specified access mode. The access mode is either "r" for read only access, "rw" for read write access, "rws" for synchronized read/write access of both content and metadata, or "rwd" for read/write access where only content is required to be synchronous. Note that aSecurityManager
check is made prior to opening the file to determine whether or not this file is allowed to be read or written.
- Parameters:
fileName
- The name of the file to read and/or writemode
- "r", "rw", "rws", or "rwd"
- Throws:
IllegalArgumentException
- Ifmode
has an illegal valueSecurityException
- If the requested access to the file is not allowedFileNotFoundException
- If the file is a directory or any other error occurs
public void close() throws IOException
This method closes the file and frees up all file related system resources. Since most operating systems put a limit on how many files may be opened at any given time, it is a good idea to close all files when no longer needed to avoid hitting this limit
public final FileChannel getChannel()
This method creates a java.nio.channels.FileChannel. Nio does not allow one to create a file channel directly. A file channel must be created by first creating an instance of Input/Output/RandomAccessFile and invoking the getChannel() method on it.
public final FileDescriptor getFD() throws IOException
This method returns aFileDescriptor
object that represents the native file handle for this file.
- Returns:
- The
FileDescriptor
object for this file
- Throws:
IOException
- If an error occurs
public long getFilePointer() throws IOException
This method returns the current offset in the file at which the next read or write will occur
- Returns:
- The current file position
- Throws:
IOException
- If an error occurs
public long length() throws IOException
This method returns the length of the file in bytes
- Returns:
- The length of the file
- Throws:
IOException
- If an error occurs
public int read() throws IOException
This method reads a single byte of data from the file and returns it as an integer.
- Returns:
- The byte read as an int, or -1 if the end of the file was reached.
- Throws:
IOException
- If an error occurs
public int read(byte[] buffer) throws IOException
This method reads bytes from the file into the specified array. The bytes are stored starting at the beginning of the array and up tobuf.length
bytes can be read.
- Parameters:
buffer
- The buffer to read bytes from the file into
- Returns:
- The actual number of bytes read or -1 if end of file
- Throws:
IOException
- If an error occurs
public int read(byte[] buffer, int offset, int len) throws IOException
This methods reads up tolen
bytes from the file into the specified array starting at positionoffset
into the array.
- Parameters:
buffer
- The array to read the bytes intooffset
- The index into the array to start storing byteslen
- The requested number of bytes to read
- Returns:
- The actual number of bytes read, or -1 if end of file
- Throws:
IOException
- If an error occurs
public final boolean readBoolean() throws IOException
This method reads a Java boolean value from an input stream. It does so by reading a single byte of data. If that byte is zero, then the value returned isfalse
If the byte is non-zero, then the value returned istrue
This method can read aboolean
written by an object implementing thewriteBoolean()
method in theDataOutput
interface.
- Specified by:
- readBoolean in interface DataInput
- Returns:
- The
boolean
value read
- Throws:
IOException
- If any other error occurs
public final byte readByte() throws IOException
This method reads a Java byte value from an input stream. The value is in the range of -128 to 127. This method can read abyte
written by an object implementing thewriteByte()
method in theDataOutput
interface.
- Returns:
- The
byte
value read
- Throws:
IOException
- If any other error occurs
- See Also:
DataOutput
public final char readChar() throws IOException
This method reads a Javachar
value from an input stream. It operates by reading two bytes from the stream and converting them to a single 16-bit Javachar
The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering. As an example, ifbyte1
andbyte2
represent the first and second byte read from the stream respectively, they will be transformed to achar
in the following manner:(char)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)
This method can read achar
written by an object implementing thewriteChar()
method in theDataOutput
interface.
- Returns:
- The
char
value read
- Throws:
IOException
- If any other error occurs
- See Also:
DataOutput
public final double readDouble() throws IOException
This method reads a Java double value from an input stream. It operates by first reading alogn
value from the stream by calling thereadLong()
method in this interface, then converts thatlong
to adouble
using thelongBitsToDouble
method in the classjava.lang.Double
This method can read adouble
written by an object implementing thewriteDouble()
method in theDataOutput
interface.
- Specified by:
- readDouble in interface DataInput
- Returns:
- The
double
value read
- Throws:
IOException
- If any other error occurs
- See Also:
Double
,DataOutput
public final float readFloat() throws IOException
This method reads a Java float value from an input stream. It operates by first reading anint
value from the stream by calling thereadInt()
method in this interface, then converts thatint
to afloat
using theintBitsToFloat
method in the classjava.lang.Float
This method can read afloat
written by an object implementing thewriteFloat()
method in theDataOutput
interface.
- Returns:
- The
float
value read
- Throws:
IOException
- If any other error occurs
- See Also:
Float
,DataOutput
public final void readFully(byte[] buffer) throws IOException
This method reads raw bytes into the passed array until the array is full. Note that this method blocks until the data is available and throws an exception if there is not enough data left in the stream to fill the buffer
- Parameters:
buffer
- The buffer into which to read the data
- Throws:
IOException
- If any other error occurs
public final void readFully(byte[] buffer, int offset, int count) throws IOException
This method reads raw bytes into the passed arraybuf
startingoffset
bytes into the buffer. The number of bytes read will be exactlylen
Note that this method blocks until the data is available and throws an exception if there is not enough data left in the stream to readlen
bytes.
- Parameters:
buffer
- The buffer into which to read the dataoffset
- The offset into the buffer to start storing datacount
- The number of bytes to read into the buffer
- Throws:
IOException
- If any other error occurs
public final int readInt() throws IOException
This method reads a Javaint
value from an input stream It operates by reading four bytes from the stream and converting them to a single Javaint
The bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering. As an example, ifbyte1
throughbyte4
represent the first four bytes read from the stream, they will be transformed to anint
in the following manner:(int)(((byte1 & 0xFF) << 24) + ((byte2 & 0xFF) << 16) + ((byte3 & 0xFF) << 8) + (byte4 & 0xFF)))
The value returned is in the range of 0 to 65535. This method can read anint
written by an object implementing thewriteInt()
method in theDataOutput
interface.
- Returns:
- The
int
value read
- Throws:
IOException
- If any other error occurs
- See Also:
DataOutput
public final String readLine() throws IOException
This method reads the next line of text data from an input stream. It operates by reading bytes and converting those bytes tochar
values by treating the byte read as the low eight bits of thechar
and using0
as the high eight bits. Because of this, it does not support the full 16-bit Unicode character set. The reading of bytes ends when either the end of file or a line terminator is encountered. The bytes read are then returned as aString
A line terminator is a byte sequence consisting of either\r
\n
or\r\n
These termination charaters are discarded and are not returned as part of the string. This method can read data that was written by an object implementing thewriteLine()
method inDataOutput
- Returns:
- The line read as a
String
- Throws:
IOException
- If an error occurs
- See Also:
DataOutput
public final long readLong() throws IOException
This method reads a Java long value from an input stream It operates by reading eight bytes from the stream and converting them to a single Javalong
The bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering. As an example, ifbyte1
throughbyte8
represent the first eight bytes read from the stream, they will be transformed to anlong
in the following manner:(long)((((long)byte1 & 0xFF) << 56) + (((long)byte2 & 0xFF) << 48) + (((long)byte3 & 0xFF) << 40) + (((long)byte4 & 0xFF) << 32) + (((long)byte5 & 0xFF) << 24) + (((long)byte6 & 0xFF) << 16) + (((long)byte7 & 0xFF) << 8) + ((long)byte9 & 0xFF)))
The value returned is in the range of 0 to 65535. This method can read anlong
written by an object implementing thewriteLong()
method in theDataOutput
interface.
- Returns:
- The
long
value read
- Throws:
IOException
- If any other error occurs
- See Also:
DataOutput
public final short readShort() throws IOException
This method reads a signed 16-bit value into a Java in from the stream. It operates by reading two bytes from the stream and converting them to a single 16-bit Javashort
The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering. As an example, ifbyte1
andbyte2
represent the first and second byte read from the stream respectively, they will be transformed to ashort
in the following manner:(short)(((byte1 & 0xFF) << 8) | (byte2 & 0xFF)
The value returned is in the range of -32768 to 32767. This method can read ashort
written by an object implementing thewriteShort()
method in theDataOutput
interface.
- Returns:
- The
short
value read
- Throws:
IOException
- If any other error occurs
- See Also:
DataOutput
public final String readUTF() throws IOException
This method reads aString
from an input stream that is encoded in a modified UTF-8 format. This format has a leading two byte sequence that contains the remaining number of bytes to read. This two byte sequence is read using thereadUnsignedShort()
method of this interface. After the number of remaining bytes have been determined, these bytes are read an transformed intochar
values. Thesechar
values are encoded in the stream using either a one, two, or three byte format. The particular format in use can be determined by examining the first byte read. If the first byte has a high order bit of 0 then that character consists on only one byte. This character value consists of seven bits that are at positions 0 through 6 of the byte. As an example, ifbyte1
is the byte read from the stream, it would be converted to achar
like so:(char)byte1
If the first byte has110
as its high order bits, then the character consists of two bytes. The bits that make up the character value are in positions 0 through 4 of the first byte and bit positions 0 through 5 of the second byte. (The second byte should have 10 as its high order bits). These values are in most significant byte first (i.e., "big endian") order. As an example, ifbyte1
andbyte2
are the first two bytes read respectively, and the high order bits of them match the patterns which indicate a two byte character encoding, then they would be converted to a Javachar
like so:(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))
If the first byte has a1110
as its high order bits, then the character consists of three bytes. The bits that make up the character value are in positions 0 through 3 of the first byte and bit positions 0 through 5 of the other two bytes. (The second and third bytes should have10
as their high order bits). These values are in most significant byte first (i.e., "big endian") order. As an example, ifbyte1
byte2
andbyte3
are the three bytes read, and the high order bits of them match the patterns which indicate a three byte character encoding, then they would be converted to a Javachar
like so:(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) | (byte3 & 0x3F))
Note that all characters are encoded in the method that requires the fewest number of bytes with the exception of the character with the value of\u0000
which is encoded as two bytes. This is a modification of the UTF standard used to prevent C language styleNUL
values from appearing in the byte stream. This method can read data that was written by an object implementing thewriteUTF()
method inDataOutput
- Returns:
- The
String
read
- Throws:
IOException
- If any other error occurs
- See Also:
DataOutput
public final int readUnsignedByte() throws IOException
This method reads 8 unsigned bits into a Javaint
value from the stream. The value returned is in the range of 0 to 255. This method can read an unsigned byte written by an object implementing thewriteUnsignedByte()
method in theDataOutput
interface.
- Specified by:
- readUnsignedByte in interface DataInput
- Returns:
- The unsigned bytes value read as a Java
int
- Throws:
IOException
- If any other error occurs
- See Also:
DataOutput
public final int readUnsignedShort() throws IOException
This method reads 16 unsigned bits into a Java int value from the stream. It operates by reading two bytes from the stream and converting them to a single Javaint
The two bytes are stored most significant byte first (i.e., "big endian") regardless of the native host byte ordering. As an example, ifbyte1
andbyte2
represent the first and second byte read from the stream respectively, they will be transformed to anint
in the following manner:(int)(((byte1 & 0xFF) << 8) + (byte2 & 0xFF))
The value returned is in the range of 0 to 65535. This method can read an unsigned short written by an object implementing thewriteUnsignedShort()
method in theDataOutput
interface.
- Specified by:
- readUnsignedShort in interface DataInput
- Returns:
- The unsigned short value read as a Java
int
- Throws:
IOException
- If any other error occurs
public void seek(long pos) throws IOException
This method sets the current file position to the specified offset from the beginning of the file. Note that some operating systems will allow the file pointer to be set past the current end of the file.
- Parameters:
pos
- The offset from the beginning of the file at which to set the file pointer
- Throws:
IOException
- If an error occurs
public void setLength(long newLen) throws IOException
This method sets the length of the file to the specified length. If the currently length of the file is longer than the specified length, then the file is truncated to the specified length (the file position is set to the end of file in this case). If the current length of the file is shorter than the specified length, the file is extended with bytes of an undefined value (the file position is unchanged in this case). The file must be open for write access for this operation to succeed.
- Parameters:
newLen
- The new length of the file
- Throws:
IOException
- If an error occurs
public int skipBytes(int numBytes) throws IOException
This method attempts to skip and discard the specified number of bytes in the input stream. It may actually skip fewer bytes than requested. The actual number of bytes skipped is returned. This method will not skip any bytes if passed a negative number of bytes to skip.
- Parameters:
numBytes
- The requested number of bytes to skip.
- Returns:
- The number of bytes actually skipped.
- Throws:
IOException
- If an error occurs.
public void write(byte[] buffer) throws IOException
This method writes all the bytes in the specified array to the file. The file must be open read-write in order for this operation to succeed.
- Specified by:
- write in interface DataOutput
- Parameters:
buffer
- The array of bytes to write to the file
public void write(byte[] buffer, int offset, int len) throws IOException
This method writeslen
bytes to the file from the specified array starting at indexoffset
into the array.
- Specified by:
- write in interface DataOutput
- Parameters:
buffer
- The array of bytes to write to the fileoffset
- The index into the array to start writing filelen
- The number of bytes to write
- Throws:
IOException
- If an error occurs
public void write(int oneByte) throws IOException
This method writes a single byte of data to the file. The file must be open for read-write in order for this operation to succeed.
- Specified by:
- write in interface DataOutput
- Parameters:
oneByte
- The byte of data to write, passed as an int.
- Throws:
IOException
- If an error occurs
public final void writeBoolean(boolean val) throws IOException
This method writes a Javaboolean
to the underlying output stream. For a value oftrue
, 1 is written to the stream. For a value offalse
, 0 is written.
- Specified by:
- writeBoolean in interface DataOutput
- Parameters:
val
- Theboolean
value to write to the stream
- Throws:
IOException
- If an error occurs
public final void writeByte(int val) throws IOException
This method writes a Javabyte
value to the underlying output stream.
- Specified by:
- writeByte in interface DataOutput
- Parameters:
val
- Thebyte
to write to the stream, passed as anint
.
- Throws:
IOException
- If an error occurs
public final void writeBytes(String val) throws IOException
This method writes all the bytes in aString
out to the stream. One byte is written for each character in theString
. The high eight bits of each character are discarded.
- Specified by:
- writeBytes in interface DataOutput
- Parameters:
val
- TheString
to write to the stream
- Throws:
IOException
- If an error occurs
public final void writeChar(int val) throws IOException
This method writes a singlechar
value to the stream, high byte first.
- Specified by:
- writeChar in interface DataOutput
- Parameters:
val
- Thechar
value to write, passed as anint
.
- Throws:
IOException
- If an error occurs
public final void writeChars(String val) throws IOException
This method writes all the characters in aString
to the stream. There will be two bytes for each character value. The high byte of the character will be written first.
- Specified by:
- writeChars in interface DataOutput
- Parameters:
val
- TheString
to write to the stream.
- Throws:
IOException
- If an error occurs
public final void writeDouble(double val) throws IOException
This method writes a Javadouble
value to the stream. This value is written by first calling the methodDouble.doubleToLongBits
to retrieve anlong
representing the floating point number, then writing thislong
value to the stream exactly the same as thewriteLong()
method does.
- Specified by:
- writeDouble in interface DataOutput
- Parameters:
val
- The double precision floating point number to write to the stream.
- Throws:
IOException
- If an error occurs
- See Also:
writeLong(long)
public final void writeFloat(float val) throws IOException
This method writes a Javafloat
value to the stream. This value is written by first calling the methodFloat.floatToIntBits
to retrieve anint
representing the floating point number, then writing thisint
value to the stream exactly the same as thewriteInt()
method does.
- Specified by:
- writeFloat in interface DataOutput
- Parameters:
val
- The floating point number to write to the stream.
- Throws:
IOException
- If an error occurs
- See Also:
writeInt(int)
public final void writeInt(int val) throws IOException
This method writes a Javaint
to the stream, high bytes first. This method requires four bytes to encode the value.
- Specified by:
- writeInt in interface DataOutput
- Parameters:
val
- Theint
value to write to the stream.
- Throws:
IOException
- If an error occurs
public final void writeLong(long val) throws IOException
This method writes a Javalong
to the stream, high bytes first. This method requires eight bytes to encode the value.
- Specified by:
- writeLong in interface DataOutput
- Parameters:
val
- Thelong
value to write to the stream.
- Throws:
IOException
- If an error occurs
public final void writeShort(int val) throws IOException
This method writes a Javashort
to the stream, high byte first. This method requires two bytes to encode the value.
- Specified by:
- writeShort in interface DataOutput
- Parameters:
val
- Theshort
value to write to the stream, passed as anint
.
- Throws:
IOException
- If an error occurs
public final void writeUTF(String val) throws IOException
This method writes a JavaString
to the stream in a modified UTF-8 format. First, two bytes are written to the stream indicating the number of bytes to follow. Note that this is the number of bytes in the encodedString
not theString
length. Next come the encoded characters. Each character in theString
is encoded as either one, two or three bytes. For characters in the range of\u0001
to\u007F
, one byte is used. The character value goes into bits 0-7 and bit eight is 0. For characters in the range of\u0080
to\u007FF
, two bytes are used. Bits 6-10 of the character value are encoded bits 0-4 of the first byte, with the high bytes having a value of "110". Bits 0-5 of the character value are stored in bits 0-5 of the second byte, with the high bits set to "10". This type of encoding is also done for the null character\u0000
. This eliminates any C style NUL character values in the output. All remaining characters are stored as three bytes. Bits 12-15 of the character value are stored in bits 0-3 of the first byte. The high bits of the first bytes are set to "1110". Bits 6-11 of the character value are stored in bits 0-5 of the second byte. The high bits of the second byte are set to "10". And bits 0-5 of the character value are stored in bits 0-5 of byte three, with the high bits of that byte set to "10".
- Specified by:
- writeUTF in interface DataOutput
- Parameters:
val
- TheString
to write to the output in UTF format
- Throws:
IOException
- If an error occurs
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