java.io DataInput

java.io
DataInput

Declaration
public interface DataInput
All Known Subinterfaces: javax.microedition.io.Datagram
All Known Implementing Classes: DataInputStream
Description
The DataInput interface provides for reading bytes from a binary stream and reconstructing from them data
in any of the Java primitive types. There is also a facility for reconstructing a String from data in Java
modified UTF-8 format.
It is generally true of all the reading routines in this interface 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 input stream has been closed.


Methods
boolean readBoolean()
byte readByte()
char readChar()
double readDouble()
float readFloat()
void readFully(byte[] b)
void readFully(byte[] b, int off, int len)
int readInt()
long readLong()
short readShort()
int readUnsignedByte()
int readUnsignedShort()
java.lang.String readUTF()
int skipBytes(int n)



Methods
readFully(byte[])
Declaration:
public void readFully(byte[] b)
throws IOException
Description:
Reads some bytes from an input stream and stores them into the buffer array b. The number of bytes read is
equal to the length of b.
This method blocks until one of the following conditions occurs:
• b.length bytes of input data are available, in which case a normal return is made.
• End of file is detected, in which case an EOFException is thrown.
• An I/O error occurs, in which case an IOException other than EOFException is thrown.
If b is null, a NullPointerException is thrown. If b.length is zero, then no bytes are read.
Otherwise, the first byte read is stored into element b[0], the next one into b[1], and so on. If an
exception is thrown from this method, then it may be that some but not all bytes of b have been updated
with data from the input stream.
Parameters:
b - the buffer into which the data is read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
readFully(byte[], int, int)
Declaration:
public void readFully(byte[] b, int off, int len)
throws IOException
Description:
Reads len bytes from an input stream.
This method blocks until one of the following conditions occurs:
• len bytes of input data are available, in which case a normal return is made.
• End of file is detected, in which case an EOFException is thrown.
• An I/O error occurs, in which case an IOException other than EOFException is thrown.
If b is null, a NullPointerException is thrown. If off is negative, or len is negative, or
off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown.
If len is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[off], the
next one into b[off+1], and so on. The number of bytes read is, at most, equal to len.
Parameters:
b - the buffer into which the data is read.
off - an int specifying the offset into the data.
len - an int specifying the number of bytes to read.

skipBytes(int)
14
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
skipBytes(int)
Declaration:
public int skipBytes(int n)
throws IOException
Description:
Makes an attempt to skip over n bytes of data from the input stream, discarding the skipped bytes.
However, it 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 n bytes have been skipped is only one possibility. This
method never throws an EOFException. The actual number of bytes skipped is returned.
Parameters:
n - the number of bytes to be skipped.
Returns: the actual number of bytes skipped.
Throws:
IOException - if an I/O error occurs.
readBoolean()
Declaration:
public boolean readBoolean()
throws IOException
Description:
Reads one input byte and returns true if that byte is nonzero, false if that byte is zero. This method is
suitable for reading the byte written by the writeBoolean method of interface DataOutput.
Returns: the boolean value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
readByte()
Declaration:
public byte readByte()
throws IOException
Description:
Reads and returns one input byte. The byte is treated as a signed value in the range -128 through 127,
inclusive. This method is suitable for reading the byte written by the writeByte method of interface
DataOutput.
Returns: the 8-bit value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readUnsignedByte()
Declaration:
public int readUnsignedByte()
throws IOException
Description:
Reads one input byte, zero-extends it to type int, and returns the result, which is therefore in the range 0
through 255. This method is suitable for reading the byte written by the writeByte method of interface
DataOutput if the argument to writeByte was intended to be a value in the range 0 through 255.
Returns: the unsigned 8-bit value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
readShort()
Declaration:
public short readShort()
throws IOException
Description:
Reads two input bytes and returns a short value. Let a be the first byte read and b be the second byte. The
value returned is:
(short)((a << 8) | (b & 0xff))
This method is suitable for reading the bytes written by the writeShort method of interface
DataOutput.
Returns: the 16-bit value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
readUnsignedShort()
Declaration:
public int readUnsignedShort()
throws IOException
Description:
Reads two input bytes, zero-extends it to type int, and returns an int value in the range 0 through
65535. Let a be the first byte read and b be the second byte. The value returned is:
(((a & 0xff) << 8) | (b & 0xff))
This method is suitable for reading the bytes written by the writeShort method of interface
DataOutput if the argument to writeShort was intended to be a value in the range 0 through 65535.
Returns: the unsigned 16-bit value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readChar()
Declaration:
public char readChar()
throws IOException
Description:
Reads an input char and returns the char value. A Unicode char is made up of two bytes. Let a be the
first byte read and b be the second byte. The value returned is:
(char)((a << 8) | (b & 0xff))
This method is suitable for reading bytes written by the writeChar method of interface DataOutput.
Returns: the Unicode char read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
readInt()
Declaration:
public int readInt()
throws IOException
Description:
Reads four input bytes and returns an int value. Let a be the first byte read, b be the second byte, c be the
third byte, and d be the fourth byte. The value returned is:
(((a & 0xff) << 24) | ((b & 0xff) << 16) |
&#32;((c & 0xff) << 8) | (d & 0xff))
This method is suitable for reading bytes written by the writeInt method of interface DataOutput.
Returns: the int value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
readLong()
Declaration:
public long readLong()
throws IOException
Description:
Reads eight input bytes and returns a long value. Let a be the first byte read, b be the second byte, c be
the third byte, d be the fourth byte, e be the fifth byte, f be the sixth byte, g be the seventh byte, and h be
the eighth byte. The value returned is:

(((long)(a & 0xff) << 56) |
((long)(b & 0xff) << 48) |
((long)(c & 0xff) << 40) |
((long)(d & 0xff) << 32) |
((long)(e & 0xff) << 24) |
((long)(f & 0xff) << 16) |
((long)(g & 0xff) << 8) |
((long)(h & 0xff)))
This method is suitable for reading bytes written by the writeLong method of interface DataOutput.
Returns: the long value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
readFloat()
Declaration:
public float readFloat()
throws IOException
Description:
Reads four input bytes and returns a float value. It does this by first constructing an int value in exactly
the manner of the readInt method, then converting this int value to a float in exactly the manner of
the method Float.intBitsToFloat. This method is suitable for reading bytes written by the
writeFloat method of interface DataOutput.
Returns: the float value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
Since: CLDC 1.1
readDouble()
Declaration:
public double readDouble()
throws IOException
Description:
Reads eight input bytes and returns a double value. It does this by first constructing a long value in
exactly the manner of the readlong method, then converting this long value to a double in exactly the
manner of the method Double.longBitsToDouble. This method is suitable for reading bytes written
by the writeDouble method of interface DataOutput.
Returns: the double value read.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
Since: CLDC 1.1


readUTF()
Declaration:
public java.lang.String readUTF()
throws IOException
Description:
Reads in a string that has been encoded using a modified UTF-8 format. The general contract of readUTF
is that it reads a representation of a Unicode character string encoded in Java modified UTF-8 format; this
string of characters is then returned as a String.
First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the
readUnsignedShort method . This integer value is called the UTF length and specifies the number of
additional bytes to be read. These bytes are then converted to characters by considering them in groups. The
length of each group is computed from the value of the first byte of the group. The byte following a group,
if any, is the first byte of the next group.
If the first byte of a group matches the bit pattern 0xxxxxxx (where x means “may be 0 or 1”), then the
group consists of just that byte. The byte is zero-extended to form a character.
If the first byte of a group matches the bit pattern 110xxxxx, then the group consists of that byte a and a
second byte b. If there is no byte b (because byte a was the last of the bytes to be read), or if byte b does
not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the
group is converted to the character:
(char)(((a& 0x1F) << 6) | (b & 0x3F))
If the first byte of a group matches the bit pattern 1110xxxx, then the group consists of that byte a and
two more bytes b and c. If there is no byte c (because byte a was one of the last two of the bytes to be
read), or either byte b or byte c does not match the bit pattern 10xxxxxx, then a
UTFDataFormatException is thrown. Otherwise, the group is converted to the character:
(char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))
If the first byte of a group matches the pattern 1111xxxx or the pattern 10xxxxxx, then a
UTFDataFormatException is thrown.
If end of file is encountered at any time during this entire process, then an EOFException is thrown.
After every group has been converted to a character by this process, the characters are gathered, in the same
order in which their corresponding groups were read from the input stream, to form a String, which is
returned.
The writeUTF method of interface DataOutput may be used to write data that is suitable for reading
by this method.
Returns: a Unicode string.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
UTFDataFormatException - if the bytes do not represent a valid UTF-8 encoding of a string.