java.io

Class DataInputStream

java.lang.Object

java.io.InputStream

java.io.FilterInputStream

java.io.DataInputStream

All Implemented Interfaces:

DataInput

public class DataInputStream
extends FilterInputStream
implements DataInput

A data input stream lets an application read primitive Java data types from an underlying input stream in a machine-independent way. An application uses a data output stream to write data that can later be read by a data input stream.

Data input streams and data output streams represent Unicode strings in a format that is a slight modification of UTF-8. (For more information, see X/Open Company Ltd., "File System Safe UCS Transformation Format (FSS_UTF)", X/Open Preliminary Specification, Document Number: P316. This information also appears in ISO/IEC 10646, Annex P.) Note that in the following tables, the most significant bit appears in the far left-hand column.

All characters in the range '\u0001' to '\u007F' are represented by a single byte:

	Bit Values
Byte 1	0	bits 6-0

The null character '\u0000' and characters in the range '\u0080' to '\u07FF' are represented by a pair of bytes:

	Bit Values
Byte 1	1	1	0	bits 10-6
Byte 2	1	0	bits 5-0

Characters in the range '\u0800' to '\uFFFF' are represented by three bytes:

	Bit Values
Byte 1	1	1	1	0	bits 15-12
Byte 2	1	0	bits 11-6
Byte 3	1	0	bits 5-0

The two differences between this format and the "standard" UTF-8 format are the following:

• The null byte '\u0000' is encoded in 2-byte format rather than 1-byte, so that the encoded strings never have embedded nulls.
• Only the 1-byte, 2-byte, and 3-byte formats are used.

Since:

JDK1.0

Version:

1.52 10/17/00

Author:

Arthur van Hoff

See Also:

DataOutputStream

Field Summary

Fields inherited from class java.io.FilterInputStream

in

Constructor Summary

Constructors

Constructor and Description
DataInputStream(InputStream in) Creates a DataInputStream that uses the specified underlying InputStream.

Method Summary

Methods

Modifier and Type	Method and Description
int	read(byte[] b) Reads some number of bytes from the contained input stream and stores them into the buffer array b.
int	read(byte[] b, int off, int len) Reads up to len bytes of data from the contained input stream into an array of bytes.
boolean	readBoolean() See the general contract of the readBoolean method of DataInput.
byte	readByte() See the general contract of the readByte method of DataInput.
char	readChar() See the general contract of the readChar method of DataInput.
double	readDouble() See the general contract of the readDouble method of DataInput.
float	readFloat() See the general contract of the readFloat method of DataInput.
void	readFully(byte[] b) See the general contract of the readFully method of DataInput.
void	readFully(byte[] b, int off, int len) See the general contract of the readFully method of DataInput.
int	readInt() See the general contract of the readInt method of DataInput.
String	readLine() Deprecated. This method does not properly convert bytes to characters. As of JDK 1.1, the preferred way to read lines of text is via the BufferedReader.readLine() method. Programs that use the DataInputStream class to read lines can be converted to use the BufferedReader class by replacing code of the form: DataInputStream d = new DataInputStream(in); with: BufferedReader d = new BufferedReader(new InputStreamReader(in));
long	readLong() See the general contract of the readLong method of DataInput.
short	readShort() See the general contract of the readShort method of DataInput.
int	readUnsignedByte() See the general contract of the readUnsignedByte method of DataInput.
int	readUnsignedShort() See the general contract of the readUnsignedShort method of DataInput.
String	readUTF() See the general contract of the readUTF method of DataInput.
static String	readUTF(DataInput in) Reads from the stream in a representation of a Unicode character string encoded in Java modified UTF-8 format; this string of characters is then returned as a String.
int	skipBytes(int n) See the general contract of the skipBytes method of DataInput.

Methods inherited from class java.io.FilterInputStream

available, close, mark, markSupported, read, reset, skip

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DataInputStream

public DataInputStream(InputStream in)

Creates a DataInputStream that uses the specified underlying InputStream.

Parameters:

in - the specified input stream

Method Detail

read

public final int read(byte[] b)
               throws IOException

Reads some number of bytes from the contained input stream and stores them into the buffer array b. The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown.

If b is null, a NullPointerException is thrown. If the length of b is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[0], the next one into b[1], and so on. The number of bytes read is, at most, equal to the length of b. Let k be the number of bytes actually read; these bytes will be stored in elements b[0] through b[k-1], leaving elements b[k] through b[b.length-1] unaffected.

If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed.

The read(b) method has the same effect as:

 read(b, 0, b.length) 
 

Overrides:

read in class FilterInputStream

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.

Throws:

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in, InputStream.read(byte[], int, int)

read

public final int read(byte[] b,
       int off,
       int len)
               throws IOException

Reads up to len bytes of data from the contained input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read, possibly zero. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception 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 and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

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. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k] through b[off+len-1] unaffected.

In every case, elements b[0] through b[off] and elements b[off+len] through b[b.length-1] are unaffected.

If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed.

Overrides:

read in class FilterInputStream

Parameters:

b - the buffer into which the data is read.

off - the start offset of the data.

len - the maximum number of bytes 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.

Throws:

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in, InputStream.read(byte[], int, int)

readFully

public final void readFully(byte[] b)
                     throws IOException

See the general contract of the readFully method of DataInput.

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

Specified by:

readFully in interface DataInput

Parameters:

b - the buffer into which the data is read.

Throws:

EOFException - if this input stream reaches the end before reading all the bytes.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readFully

public final void readFully(byte[] b,
             int off,
             int len)
                     throws IOException

See the general contract of the readFully method of DataInput.

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

Specified by:

readFully in interface DataInput

Parameters:

b - the buffer into which the data is read.

off - the start offset of the data.

len - the number of bytes to read.

Throws:

EOFException - if this input stream reaches the end before reading all the bytes.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

skipBytes

public final int skipBytes(int n)
                    throws IOException

See the general contract of the skipBytes method of DataInput.

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

Specified by:

skipBytes in interface DataInput

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

public final boolean readBoolean()
                          throws IOException

See the general contract of the readBoolean method of DataInput.

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

Specified by:

readBoolean in interface DataInput

Returns:

the boolean value read.

Throws:

EOFException - if this input stream has reached the end.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readByte

public final byte readByte()
                    throws IOException

See the general contract of the readByte method of DataInput.

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

Specified by:

readByte in interface DataInput

Returns:

the next byte of this input stream as a signed 8-bit byte.

Throws:

EOFException - if this input stream has reached the end.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readUnsignedByte

public final int readUnsignedByte()
                           throws IOException

See the general contract of the readUnsignedByte method of DataInput.

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

Specified by:

readUnsignedByte in interface DataInput

Returns:

the next byte of this input stream, interpreted as an unsigned 8-bit number.

Throws:

EOFException - if this input stream has reached the end.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readShort

public final short readShort()
                      throws IOException

See the general contract of the readShort method of DataInput.

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

Specified by:

readShort in interface DataInput

Returns:

the next two bytes of this input stream, interpreted as a signed 16-bit number.

Throws:

EOFException - if this input stream reaches the end before reading two bytes.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readUnsignedShort

public final int readUnsignedShort()
                            throws IOException

See the general contract of the readUnsignedShort method of DataInput.

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

Specified by:

readUnsignedShort in interface DataInput

Returns:

the next two bytes of this input stream, interpreted as an unsigned 16-bit integer.

Throws:

EOFException - if this input stream reaches the end before reading two bytes.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readChar

public final char readChar()
                    throws IOException

See the general contract of the readChar method of DataInput.

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

Specified by:

readChar in interface DataInput

Returns:

the next two bytes of this input stream as a Unicode character.

Throws:

EOFException - if this input stream reaches the end before reading two bytes.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readInt

public final int readInt()
                  throws IOException

See the general contract of the readInt method of DataInput.

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

Specified by:

readInt in interface DataInput

Returns:

the next four bytes of this input stream, interpreted as an int.

Throws:

EOFException - if this input stream reaches the end before reading four bytes.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readLong

public final long readLong()
                    throws IOException

See the general contract of the readLong method of DataInput.

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

Specified by:

readLong in interface DataInput

Returns:

the next eight bytes of this input stream, interpreted as a long.

Throws:

EOFException - if this input stream reaches the end before reading eight bytes.

IOException - if an I/O error occurs.

See Also:

FilterInputStream.in

readFloat

public final float readFloat()
                      throws IOException

See the general contract of the readFloat method of DataInput.

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

Specified by:

readFloat in interface DataInput

Returns:

the next four bytes of this input stream, interpreted as a float.

Throws:

EOFException - if this input stream reaches the end before reading four bytes.

IOException - if an I/O error occurs.

See Also:

readInt(), Float.intBitsToFloat(int)

readDouble

public final double readDouble()
                        throws IOException

See the general contract of the readDouble method of DataInput.

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

Specified by:

readDouble in interface DataInput

Returns:

the next eight bytes of this input stream, interpreted as a double.

Throws:

EOFException - if this input stream reaches the end before reading eight bytes.

IOException - if an I/O error occurs.

See Also:

readLong(), Double.longBitsToDouble(long)

readLine

public final String readLine()
                      throws IOException

Deprecated. This method does not properly convert bytes to characters. As of JDK 1.1, the preferred way to read lines of text is via the BufferedReader.readLine() method. Programs that use the DataInputStream class to read lines can be converted to use the BufferedReader class by replacing code of the form:

     DataInputStream d = new DataInputStream(in);
 

with:

     BufferedReader d
          = new BufferedReader(new InputStreamReader(in));
 

See the general contract of the readLine method of DataInput.

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

Specified by:

readLine in interface DataInput

Returns:

the next line of text from this input stream.

Throws:

IOException - if an I/O error occurs.

See Also:

BufferedReader.readLine(), FilterInputStream.in

readUTF

public final String readUTF()
                     throws IOException

See the general contract of the readUTF method of DataInput.

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

Specified by:

readUTF in interface DataInput

Returns:

a Unicode string.

Throws:

EOFException - if this input 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.

See Also:

readUTF(java.io.DataInput)

readUTF

public static final String readUTF(DataInput in)
                            throws IOException

Reads from the stream in a representation of a Unicode character string encoded in Java modified UTF-8 format; this string of characters is then returned as a String. The details of the modified UTF-8 representation are exactly the same as for the readUTF method of DataInput.

Parameters:

in - a data input stream.

Returns:

a Unicode string.

Throws:

EOFException - if the input stream reaches the end before all the bytes.

IOException - if an I/O error occurs.

UTFDataFormatException - if the bytes do not represent a valid Java modified UTF-8 encoding of a Unicode string.

See Also:

readUnsignedShort()