Java IO.pdf - Nguyen Dang Binh

Java I/O
the java.io.DataOutput interface declares 14 methods, mostly complementary to those in
DataInput:
public abstract void write(int b) throws IOException
public abstract void write(byte[] data) throws IOException
public abstract void write(byte[] data, int offset, int length)
throws IOException
public abstract void writeBoolean(boolean v) throws IOException
public abstract void writeByte(int b) throws IOException
public abstract void writeShort(int s) throws IOException
public abstract void writeChar(int c) throws IOException
public abstract void writeInt(int i) throws IOException
public abstract void writeLong(long l) throws IOException
public abstract void writeFloat(float f) throws IOException
public abstract void writeDouble(double d) throws IOException
public abstract void writeBytes(String s) throws IOException
public abstract void writeChars(String s) throws IOException
public abstract void writeUTF(String s) throws IOException
The writeBytes() and writeChars() methods are not matched by readBytes() and
readChars() methods in DataInput. The format used only writes the actual bytes and chars.
It does not write information about the length of the string passed as an argument to
writeBytes() and writeChars(), so the bytes and chars themselves cannot be easily
reassembled into a string. It is also unclear why DataOutput declares the three common
write() methods, but DataInput does not declare the three common read() methods.
However, the two readFully() methods are actually better matches for write(), since,
unlike read(), they will either fill the array or throw an exception.
Although DataInput and DataOutput say nothing about the formats in which data is read
and written, any class that implements this interface must adhere to an implicit contract,
summarized in Table 7.1.
Table 7.1. Formats Used by DataInput and DataOutput
Type Written by Read by Format
boolean writeBoolean(boolean
b)
readBoolean()
One byte, 0 if false, 1 if
true
byte writeByte(int b) readByte() One byte, two's complement
byte
array
write(byte[]
data)write(byte[]
data, int offset, int
length)
readFully(byte[]
data)readFully(byte[]
data, int offset, int
length)
short writeShort(int s) readShort()
char writeChar(int c) readChar()
int writeInt(int i) readInt()
long writeLong(long l) readLong()
float writeFloat(float f) readFloat()
double writeDouble(double d) readDouble()
The bytes in the order they
appear in the array or subarray
Two bytes, two's complement,
big- endian
Two bytes, unsigned, bigendian
Four bytes, two's complement,
big-endian
Eight bytes, two's
complement, big-endian
Four bytes, IEEE 754, bigendian
Eight bytes, IEEE 754, bigendian
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