java::io::DataInput Class Reference

Inheritance diagram for java::io::DataInput:

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java::io::DataInputStreamjava::lang::Interfacejava::lang::Object
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Collaboration diagram for java::io::DataInput:

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java::lang::Interfacejava::lang::Object
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List of all members.


Detailed 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.

Author:
Frank Yellin
Version:
1.16, 02/02/00
Since:
JDK1.0

Public Member Functions

virtual jint read ()=0
 Reads the next byte of data from the input stream.
virtual jint read (Array< jbyte > &b, jint off=0, jint len=-1)=0
 See the general contract of the read method of DataInput.
virtual jlong skip (jlong n)=0
 Skips over and discards n bytes of data from this input stream.
void readFully (Array< jbyte > &b, jint off=0, jint len=-1)
 Reads some bytes from an input stream and stores them into the buffer array b.
jint skipBytes (jint n)
 Makes an attempt to skip over n bytes of data from the input stream, discarding the skipped bytes.
jboolean readBoolean ()
 Reads one input byte and returns true if that byte is nonzero, false if that byte is zero.
virtual jbyte readByte ()
 Reads and returns one input byte.
jint readUnsignedByte ()
 Reads one input byte, zero-extends it to type int, and returns the result, which is therefore in the range 0 through 255.
virtual jshort readShort (jboolean littleEndian=false)
 Reads two input bytes and returns a short value.
jint readUnsignedShort (jboolean littleEndian=false)
 Reads two input bytes and returns an int value in the range 0 through 65535.
virtual jchar readChar (jboolean littleEndian=false)
 Reads an input char and returns the char value.
jint readInt (jboolean littleEndian=false)
 Reads four input bytes and returns an int value.
virtual jlong readLong (jboolean littleEndian=false)
 Reads eight input bytes and returns a long value.
virtual jfloat readFloat (jboolean littleEndian=false)
 Reads four input bytes and returns a float value.
jdouble readDouble (jboolean littleEndian=false)
 Reads eight input bytes and returns a double value.
Ref< StringreadLine ()
 Reads the next line of text from the input stream.
Ref< StringreadUTF ()
 Reads in a string that has been encoded using a modified UTF-8 format.

Member Function Documentation

virtual jint java::io::DataInput::read (  )  [pure virtual]

Reads the next byte of data from the input stream.

The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

A subclass must provide an implementation of this method.

Returns:
the next byte of data, or -1 if the end of the stream is reached.
Exceptions:
IOException if an I/O error occurs.

Implemented in java::io::DataInputStream.

virtual jint java::io::DataInput::read ( Array< jbyte > &  b,
jint  off = 0,
jint  len = -1 
) [pure virtual]

See the general contract of the read method of DataInput.

Bytes for this operation are read from the contained input stream.

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 the stream has been reached.
Exceptions:
IOException if an I/O error occurs.

Implemented in java::io::DataInputStream.

virtual jlong java::io::DataInput::skip ( jlong  n  )  [pure virtual]

Skips over and discards n bytes of data from this input stream.

The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. If n is negative, no bytes are skipped.

The skip method of InputStream creates a byte array and then repeatedly reads into it until n bytes have been read or the end of the stream has been reached. Subclasses are encouraged to provide a more efficient implementation of this method.

Parameters:
n the number of bytes to be skipped.
Returns:
the actual number of bytes skipped.
Exceptions:
IOException if an I/O error occurs.

Implemented in java::io::DataInputStream.

void java::io::DataInput::readFully ( Array< jbyte > &  b,
jint  off = 0,
jint  len = -1 
)

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:

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

jint java::io::DataInput::skipBytes ( jint  n  ) 

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 number of bytes skipped, which is always n.
Exceptions:
EOFException if this stream reaches the end before skipping all the bytes.
IOException if an I/O error occurs.

jboolean java::io::DataInput::readBoolean (  ) 

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

virtual jbyte java::io::DataInput::readByte (  )  [virtual]

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

jint java::io::DataInput::readUnsignedByte (  ) 

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

virtual jshort java::io::DataInput::readShort ( jboolean  littleEndian = false  )  [virtual]

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

jint java::io::DataInput::readUnsignedShort ( jboolean  littleEndian = false  ) 

Reads two input bytes 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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

virtual jchar java::io::DataInput::readChar ( jboolean  littleEndian = false  )  [virtual]

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

jint java::io::DataInput::readInt ( jboolean  littleEndian = false  ) 

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

virtual jlong java::io::DataInput::readLong ( jboolean  littleEndian = false  )  [virtual]

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

virtual jfloat java::io::DataInput::readFloat ( jboolean  littleEndian = false  )  [virtual]

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

jdouble java::io::DataInput::readDouble ( jboolean  littleEndian = false  ) 

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.
Exceptions:
EOFException if this stream reaches the end before reading all the bytes.
IOException if an I/O error occurs.

Ref<String> java::io::DataInput::readLine (  ) 

Reads the next line of text from the input stream.

It reads successive bytes, converting each byte separately into a character, until it encounters a line terminator or end of file; the characters read are then returned as a String. Note that because this method processes bytes, it does not support input of the full Unicode character set.

If end of file is encountered before even one byte can be read, then null is returned. Otherwise, each byte that is read is converted to type char by zero-extension. If the character '
'
is encountered, it is discarded and reading ceases. If the character '' is encountered, it is discarded and, if the following byte converts &#32;to the character '
'
, then that is discarded also; reading then ceases. If end of file is encountered before either of the characters '
'
and '' is encountered, reading ceases. Once reading has ceased, a String is returned that contains all the characters read and not discarded, taken in order. Note that every character in this string will have a value less than &#92;u0100, that is, (char)256.

Returns:
if this stream reaches the end before reading all the bytes.
Exceptions:
IOException if an I/O error occurs.

Ref<String> java::io::DataInput::readUTF (  ) 

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.
Exceptions:
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.


The documentation for this class was generated from the following file:
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