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§2.5 Class DataInputStream
public class java.io.DataInputStream
extends java.io.FilterInputStream (I-§2.11)
implements java.io.DataInput (I-§2.24)
{
// Constructors
public DataInputStream(InputStream in); §2.5.1
// Methods
public final int read(byte b[]); §2.5.2
public final int read(byte b[], int off, int len); §2.5.3
public final boolean readBoolean(); §2.5.4
public final byte readByte(); §2.5.5
public final char readChar(); §2.5.6
public final double readDouble(); §2.5.7
public final float readFloat(); §2.5.8
public final void readFully(byte b[]); §2.5.9
public final void readFully(byte b[], int off, int len); §2.5.10
public final int readInt(); §2.5.11
public final String readLine(); §2.5.12
public final long readLong(); §2.5.13
public final short readShort(); §2.5.14
public final int readUnsignedByte(); §2.5.15
public final int readUnsignedShort(); §2.5.16
public final String readUTF(); §2.5.17
public final static String readUTF(DataInput in); §2.5.18
public final int skipBytes(int n); §2.5.19
}
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
(I-§2.6) to write data which 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-81 All characters in the range '\u0001' to '\u007F' are represented
by a single byte:
The null character '\u0000' and characters in the range '\u0080' to '\u07FF' are represented by
a pair of bytes:
Characters in the range '\u0800' to '\uFFFF' are represented by three bytes:
The two differences between this format and the "standard" UTF-8 format are the following:
DataInputStream
public DataInputStream(InputStream in)
- Creates a new data input stream to read data from the specified input
stream.
- Parameters:
in
-
the input stream
read
public final int read(byte b[])
throws IOException
- Reads up to byte.length bytes of data from this data input stream into an
array of bytes. This method blocks until some input is available.
- The read method of DataInputStream calls the the read method (I-§2.13.8) of
its underlying input stream (I-§2.11.1) with the three arguments b, 0, and
b.length, and returns whatever value that method returns.
- Parameters:
b
-
the buffer into which the data is read
- Returns:
- the total number of bytes read into the buffer, or -1 is there is no more
data because the end of the stream has been reached.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
- Overrides:
- read in class FilterInputStream (I-§2.11.8).
read
public final int read(byte b[], int off, int len)
throws IOException
- Reads up to len bytes of data from this data input stream into an array of
bytes. This method blocks until some input is available.
- The read method of DataInputStream calls the read method (I-§2.13.8) of its
underlying input stream (I-§2.11.1) with the same arguments and returns
whatever value that method returns.
- 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 is there is no more
data because the end of the stream has been reached.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
- Overrides:
- read in class FilterInputStream (I-§2.11.9).
readBoolean
public final boolean readBoolean()
throws IOException
- Reads a boolean from this data input stream. This method reads a single
byte from the underlying input stream (I-§2.11.1). A value of 0 represents
false. Any other value represents true. This method blocks until either the
byte is read, the end of the stream is detected, or an exception is thrown.
- Returns:
- the boolean value read.
- Throws
- EOFException (I-§2.24)
- If this input stream has reached the end.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readByte
public final byte readByte()
throws IOException
- Reads a signed 8-bit value from this data input stream. This method reads
a byte from the underlying input stream (I-§2.11.1). If the byte read is b,
where , then the result is
readChar
public final char readChar()
throws IOException
- Reads a Unicode character from this data input stream. This method reads
two bytes from the underlying input stream (I-§2.11.1). If the bytes read,
in order, are b1 and b2, where , then the result is equal to
readDouble
public final double readDouble()
throws IOException
- Reads a double from this data input stream. This method reads a long value
as if by the readLong method (I-§2.5.13) and then converts that long to a double using the long-Bits-To-Double method (I-§1.6.18) in class Double.
- This method blocks until either the eight bytes are read, the end of the
stream is detected, or an exception is thrown.
- Returns:
- the next eight bytes of this input stream, interpreted as a double.
- Throws
- EOFException (I-§2.24)
- If this input stream reaches the end before reading eight bytes.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readFloat
public final float readFloat()
throws IOException
- Reads a float from this data input stream. This method reads an int value as
if by the readInt method (I-§2.5.11) and then converts that int to a float using
the intBitsToFloat method (I-§1.7.14) in class Float. This method blocks until
either the four bytes are read, the end of the stream is detected, or an
exception is thrown.
- Returns:
- the next four bytes of this input stream, interpreted as a float.
- Throws
- EOFException (I-§2.24)
- If this input stream reaches the end before reading four bytes.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readFully
public final void readFully(byte b[])
throws IOException
- Reads b.length bytes from this data input stream into the byte array. This
method reads repeatedly from the underlying stream (I-§2.11.1) until all
the bytes are read. This method blocks until either all the bytes are read,
the end of the stream is detected, or an exception is thrown.
- Parameters:
b
-
the buffer into which the data is read
- Throws
- EOFException (I-§2.24)
- If this input stream reaches the end before reading all the bytes.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readFully
public final void readFully(byte b[], int off, int len)
throws IOException
- Reads exactly len bytes from this data input stream into the byte array. This
method reads repeatedly from the underlying stream (I-§2.11.1) until all
the bytes are read. This method blocks until either all the bytes are read,
the end of the stream is detected, or an exception is thrown.
- Parameters:
b
-
the buffer into which the data is read
off
-
the start offset of the data
len
-
the number of bytes to read read
- Throws
- EOFException (I-§2.24)
- If this input stream reaches the end before reading all the bytes.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readInt
public final int readInt()
throws IOException
- Reads a signed 32-bit integer from this data input stream. This method
reads four bytes from the underlying input stream (I-§2.11.1). If the bytes
read, in order, are b1, b2, b3, and b4 where , then
the result is equal to
readLine
public final String readLine()
throws IOException
- Reads the next line of text from this data input stream. This method successively reads bytes from the underlying input stream (I-§2.11.1) until it
reaches the end of a line of text.
- A line of text is terminated by a carriage return character ('\r'), a newline
character ('\n'), a carriage return character immediately followed by a newline character, or the end of the input stream. The line-terminating character(s), if any, are included as part of the string returned.
- This method blocks until either a newline character is read, a carriage
return and the byte following it are read (to see if it is a newline), the end
of the stream is detected, or an exception is thrown.
- Returns:
- the next line of text from this input stream.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readLong
public final long readLong()
throws IOException
- Reads a signed 64-bit integer from this data input stream. This method
reads eight bytes from the underlying input stream (I-§2.11.1). If the bytes
read, in order, are b1, b2, b3, b4, b5, b6, b7, and b8, where
- ,
- then the result is equal to
readShort
public final short readShort()
throws IOException
- Reads a signed 16-bit number from this data input stream. The method
reads two bytes from the underlying input stream (I-§2.11.1). If the two
bytes read, in order, are b1 and b2, where each of the two values is between
0 and 255, inclusive, then the result is equal to:
- (short)((b1 << 8) | b2)
- This method blocks until either the two bytes are read, the end of the
stream is detected, or an exception is thrown.
- Returns:
- the next two bytes of this input stream, interpreted as a signed 16-bit
number.
- Throws
- EOFException (I-§2.24)
- If this input stream reaches the end before reading two bytes.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readUnsignedByte
public final int readUnsignedByte()
throws IOException
- Reads an unsigned 8-bit number from this data input stream. This method
reads a byte from this data input stream's underlying input stream
(I-§2.11.1) and returns that byte This method blocks until either the byte is
are read, the end of the stream is detected, or an exception is thrown.
- Returns:
- the next byte of this input stream, interpreted as an unsigned 8-bit
number.
- Throws
- EOFException (I-§2.24)
- If this input stream has reached the end.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readUnsignedShort
public final int readUnsignedShort()
throws IOException
- Reads an unsigned 16-bit number from this data input stream. This
method reads two bytes from the underlying input stream (I-§2.11.1). If
the bytes read, in order, are b1 and b2, where , then the
result is equal to
readUTF
public final String readUTF()
throws IOException
- Reads in a string which has been encoded using a modified UTF-8 format
from this data input stream. This method calls readUTF(this). See the following method for a more complete description of the format.
- This method blocks until either all the bytes are read, the end of the stream
is detected, or an exception is thrown.
- Returns:
- a Unicode string.
- Throws
- EOFException (I-§2.24)
- If this input stream reaches the end before reading all the bytes.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
readUTF
public final static String readUTF(DataInput in)
throws IOException
- Reads in a string from the specified data input stream. The string has been
encoded using a modified using a modified UTF-8 format.
- The first two bytes from are read as if by readUnsignedShort (I-§2.5.16). This
values gives the number of following bytes that are in the encoded string.
(Note: not the length of the resuling string). The following bytes are then
interpreted as bytes encoding characters in the UTF-8 format (page I-225)
and are converted into characters.
- This method blocks until all the bytes are read, the end of the stream is
detected, or an exception is thrown.
- Parameters:
in
-
a data input stream
- Returns:
- a Unicode string.
- Throws
- EOFException (I-§2.24)
- If the input stream reaches the end before all the bytes.
- Throws
- UTFDataFormatException (I-§2.31)
- If the bytes do not represent a valid UTF-8 encoding of a Unicode
string.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
skipBytes
public final int skipBytes(int n)
throws IOException
- Skips exactly n bytes of input in the underlying input stream (I-§2.11.1).
This method blocks until either all the bytes are skipped, the end of the
stream is detected, or an exception is thrown.
- Parameters:
n
-
the number of bytes to be skipped
- Returns:
- the number of bytes skipped, which is always n.
- Throws
- EOFException (I-§2.24)
- If this input stream reaches the end before skipping all the bytes.
- Throws
- IOException (I-§2.29)
- If an I/O error occurs.
1
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.
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