java.io

Class DataOutputStream

public class DataOutputStream extends FilterOutputStream implements DataOutput

This class provides a mechanism for writing primitive Java datatypes to an OutputStream in a portable way. Data written to a stream using this class can be read back in using the DataInputStream class on any platform.

Field Summary
protected int	written This is the total number of bytes that have been written to the stream by this object instance.

Constructor Summary
	DataOutputStream(OutputStream out) This method initializes an instance of `DataOutputStream` to write its data to the specified underlying `OutputStream`

Method Summary
void	flush() This method flushes any unwritten bytes to the underlying stream.
int	size() This method returns the total number of bytes that have been written to the underlying output stream so far.
void	write(int value) This method writes the specified byte (passed as an `int`) to the underlying output stream.
void	write(byte[] buf, int offset, int len) This method writes `len` bytes from the specified byte array `buf` starting at position `offset` into the buffer to the underlying output stream.
void	writeBoolean(boolean value) This method writes a Java boolean value to an output stream.
void	writeByte(int value) This method writes a Java byte value to an output stream.
void	writeBytes(String value) This method writes all the bytes in a `String` out to the stream.
void	writeChar(int value) This method writes a Java char value to an output stream.
void	writeChars(String value) This method writes all the characters of a `String` to an output stream as an array of `char`'s.
void	writeDouble(double value) This method writes a Java `double` value to the stream.
void	writeFloat(float value) This method writes a Java `float` value to the stream.
void	writeInt(int value) This method writes a Java int value to an output stream.
void	writeLong(long value) This method writes a Java long value to an output stream.
void	writeShort(int value) This method writes a Java short value to an output stream.
void	writeUTF(String value) This method writes a Java `String` to the stream in a modified UTF-8 format.

Field Detail

written

protected int written

This is the total number of bytes that have been written to the stream by this object instance.

Constructor Detail

DataOutputStream

public DataOutputStream(OutputStream out)

This method initializes an instance of DataOutputStream to write its data to the specified underlying OutputStream

Parameters: out The subordinate OutputStream to which this object will write

Method Detail

flush

public void flush()

This method flushes any unwritten bytes to the underlying stream.

Throws: IOException If an error occurs.

size

public final int size()

This method returns the total number of bytes that have been written to the underlying output stream so far. This is the value of the written instance variable

Returns: The number of bytes written to the stream.

write

public void write(int value)

This method writes the specified byte (passed as an int) to the underlying output stream.

Parameters: value The byte to write, passed as an int.

Throws: IOException If an error occurs.

write

public void write(byte[] buf, int offset, int len)

This method writes len bytes from the specified byte array buf starting at position offset into the buffer to the underlying output stream.

Parameters: buf The byte array to write from. offset The index into the byte array to start writing from. len The number of bytes to write.

Throws: IOException If an error occurs.

writeBoolean

public final void writeBoolean(boolean value)

This method writes a Java boolean value to an output stream. If value is true, a byte with the value of 1 will be written, otherwise a byte with the value of 0 will be written. The value written can be read using the readBoolean method in DataInput.

Parameters: value The boolean value to write to the stream

Throws: IOException If an error occurs

See Also: DataInput

writeByte

public final void writeByte(int value)

This method writes a Java byte value to an output stream. The byte to be written will be in the lowest 8 bits of the int value passed. The value written can be read using the readByte or readUnsignedByte methods in DataInput.

Parameters: value The byte to write to the stream, passed as the low eight bits of an int.

Throws: IOException If an error occurs

writeBytes

public final void writeBytes(String value)

This method writes all the bytes in a String out to the stream. One byte is written for each character in the String. The high eight bits of each character are discarded, thus this method is inappropriate for completely representing Unicode characters.

Parameters: value The String to write to the stream

Throws: IOException If an error occurs

writeChar

public final void writeChar(int value)

This method writes a Java char value to an output stream. The char to be written will be in the lowest 16 bits of the int value passed. These bytes will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF00) >> 8); byte1 = (byte)(value & 0x00FF);

The value written can be read using the readChar method in DataInput.

Parameters: value The char value to write, passed as an int.

Throws: IOException If an error occurs

See Also: DataInput

writeChars

public final void writeChars(String value)

This method writes all the characters of a String to an output stream as an array of char's. Each character is written using the method specified in the writeChar method.

Parameters: value The String to write to the stream

Throws: IOException If an error occurs

writeDouble

public final void writeDouble(double value)

This method writes a Java double value to the stream. This value is written by first calling the method Double.doubleToLongBits to retrieve an long representing the floating point number, then writing this long value to the stream exactly the same as the writeLong() method does. The value written can be read using the readDouble method in DataInput.

Parameters: value The double value to write to the stream

Throws: IOException If an error occurs

writeFloat

public final void writeFloat(float value)

This method writes a Java float value to the stream. This value is written by first calling the method Float.floatToIntBits to retrieve an int representing the floating point number, then writing this int value to the stream exactly the same as the writeInt() method does. The value written can be read using the readFloat method in DataInput.

Parameters: value The float value to write to the stream

Throws: IOException If an error occurs

writeInt

public final void writeInt(int value)

This method writes a Java int value to an output stream. The 4 bytes of the passed value will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF000000) >> 24); byte1 = (byte)((value & 0x00FF0000) >> 16); byte2 = (byte)((value & 0x0000FF00) >> 8); byte3 = (byte)(value & 0x000000FF);

The value written can be read using the readInt method in DataInput.

Parameters: value The int value to write to the stream

Throws: IOException If an error occurs

See Also: DataInput

writeLong

public final void writeLong(long value)

This method writes a Java long value to an output stream. The 8 bytes of the passed value will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF00000000000000L) >> 56); byte1 = (byte)((value & 0x00FF000000000000L) >> 48); byte2 = (byte)((value & 0x0000FF0000000000L) >> 40); byte3 = (byte)((value & 0x000000FF00000000L) >> 32); byte4 = (byte)((value & 0x00000000FF000000L) >> 24); byte5 = (byte)((value & 0x0000000000FF0000L) >> 16); byte6 = (byte)((value & 0x000000000000FF00L) >> 8); byte7 = (byte)(value & 0x00000000000000FFL);

The value written can be read using the readLong method in DataInput.

Parameters: value The long value to write to the stream

Throws: IOException If an error occurs

See Also: DataInput

writeShort

public final void writeShort(int value)

This method writes a Java short value to an output stream. The char to be written will be in the lowest 16 bits of the int value passed. These bytes will be written "big endian". That is, with the high byte written first in the following manner:

byte0 = (byte)((value & 0xFF00) >> 8); byte1 = (byte)(value & 0x00FF);

The value written can be read using the readShort and readUnsignedShort methods in DataInput.

Parameters: value The short value to write to the stream, passed as an int.

Throws: IOException If an error occurs

writeUTF

public final void writeUTF(String value)

This method writes a Java String 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 encoded String not the String length. Next come the encoded characters. Each character in the String is encoded as either one, two or three bytes. For characters in the range of to <>, one byte is used. The character value goes into bits 0-7 and bit eight is 0. For characters in the range of to F, 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 . 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". The value written can be read using the readUTF method in DataInput.

Parameters: value The String to write to the output in UTF format

Throws: IOException If an error occurs

See Also: DataInput