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Class java.io.DataInputStream - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.io.DataInputStream

java.lang.Object
   |
   +----java.io.InputStream
           |
           +----java.io.FilterInputStream
                   |
                   +----java.io.DataInputStream

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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.)

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

0

bits 0-7

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

1	1	0	bits 6-10
1	0	bits 0-5

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

1	1	1	0	bits 12-15
1	0	bits 6-11
1	0	bits 0-5

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.

See Also:

DataOutputStream

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DataInputStream(InputStream)

Creates a new data input stream to read data from the specified input stream.

read(byte[])

Reads up to byte.length bytes of data from this data input stream into an array of bytes.

read(byte[], int, int)

Reads up to len bytes of data from this data input stream into an array of bytes.

readBoolean()

Reads a boolean from this data input stream.

readByte()

Reads a signed 8-bit value from this data input stream.

readChar()

Reads a Unicode character from this data input stream.

readDouble()

Reads a double from this data input stream.

readFloat()

Reads a float from this data input stream.

readFully(byte[])

Reads b.length bytes from this data input stream into the byte array.

readFully(byte[], int, int)

Reads exactly len bytes from this data input stream into the byte array.

readInt()

Reads a signed 32-bit integer from this data input stream.

readLine()

Reads the next line of text from this data input stream. Deprecated.

readLong()

Reads a signed 64-bit integer from this data input stream.

readShort()

Reads a signed 16-bit number from this data input stream.

readUnsignedByte()

Reads an unsigned 8-bit number from this data input stream.

readUnsignedShort()

Reads an unsigned 16-bit number from this data input stream.

readUTF()

Reads in a string that has been encoded using a modified UTF-8 format from this data input stream.

readUTF(DataInput)

Reads in a string from the specified data input stream.

skipBytes(int)

Skips exactly n bytes of input in the underlying input stream.

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 read method of its underlying input stream 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 if there is no more data because the end of the stream has been reached.

Throws: IOException

if an I/O error occurs.

Overrides:

read in class FilterInputStream

See Also:

in, read

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 of its underlying input stream 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 if there is no more data because the end of the stream has been reached.

Throws: IOException

if an I/O error occurs.

Overrides:

read in class FilterInputStream

See Also:

in, read

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 until all the bytes are read. This method blocks until 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

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

Throws: IOException

if an I/O error occurs.

See Also:

in

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 until all the bytes are read. This method blocks until 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.

Throws: EOFException

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

Throws: IOException

if an I/O error occurs.

See Also:

in

skipBytes

 public final int skipBytes(int n) throws IOException

Skips exactly n bytes of input in the underlying input stream. This method blocks until 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

if this input stream reaches the end before skipping all the bytes.

Throws: IOException

if an I/O error occurs.

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. 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

if this input stream has reached the end.

Throws: IOException

if an I/O error occurs.

See Also:

in

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. If the byte read is b, where 0 <= b <= 255, then the result is:

(byte)(b)

This method blocks until either the byte is read, the end of the stream is detected, or an exception is thrown.

Returns:

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

Throws: EOFException

if this input stream has reached the end.

Throws: IOException

if an I/O error occurs.

See Also:

in

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 and returns that byte. This method blocks until the byte is 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

if this input stream has reached the end.

Throws: IOException

if an I/O error occurs.

See Also:

in

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. 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 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

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

Throws: IOException

if an I/O error occurs.

See Also:

in

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. If the bytes read, in order, are b1 and b2, where 0 <= b1, b2 <= 255, then the result is equal to:

(b1 << 8) | b2

This method blocks until 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 an unsigned 16-bit integer.

Throws: EOFException

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

Throws: IOException

if an I/O error occurs.

See Also:

in

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. If the bytes read, in order, are b1 and b2, where 0 <= b1, b1 <= 255, then the result is equal to:

(char)((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 as a Unicode character.

Throws: EOFException

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

Throws: IOException

if an I/O error occurs.

See Also:

in

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. If the bytes read, in order, are b1, b2, b3, and b4, where 0 <= b1, b2, b3, b4 <= 255, then the result is equal to:

(b1 << 24) | (b2 << 16) + (b3 << 8) +b4

This method blocks until 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 an int.

Throws: EOFException

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

Throws: IOException

if an I/O error occurs.

See Also:

in

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. If the bytes read, in order, are b1, b2, b3, b4, b5, b6, b7, and b8, where

0 <= b1, b2, b3, b4, b5, b6, b7, b8 <= 255,

then the result is equal to:

     ((long)b1 << 56) + ((long)b2 << 48) +
        ((long)b3 << 40) + ((long)b4 << 32) +
        ((long)b5 << 24) + (b6 << 16) +
        (b7 << 8) + b8
 

This method blocks until 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 long.

Throws: EOFException

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

Throws: IOException

if an I/O error occurs.

See Also:

in

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 and then converts that int to a float using the intBitsToFloat method in class Float. This method blocks until 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

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

Throws: IOException

if an I/O error occurs.

See Also:

readInt, intBitsToFloat

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 and then converts that long to a double using the longBitsToDouble method in class Double.

This method blocks until 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

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

Throws: IOException

if an I/O error occurs.

See Also:

readLong, longBitsToDouble

readLine

 public final String readLine() throws IOException

Note: readLine() is 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));

Reads the next line of text from this data input stream. This method successively reads bytes from the underlying input stream 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 not returned as part of the string that is returned.

This method blocks until 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, or null if no bytes are read before end-of-file is reached.

Throws: IOException

if an I/O error occurs.

See Also:

readLine, in

readUTF

 public final String readUTF() throws IOException

Reads in a string that has been encoded using a modified UTF-8 format from this data input stream. This method calls readUTF(this). See readUTF(java.io.DataInput) for a more complete description of the format.

This method blocks until all the bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:

a Unicode string.

Throws: EOFException

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

Throws: IOException

if an I/O error occurs.

See Also:

readUTF

readUTF

 public static final String readUTF(DataInput in) throws IOException

Reads in a string from the specified data input stream. The string has been encoded using a modified UTF-8 format.

The first two bytes are read as if by readUnsignedShort. This value gives the number of following bytes that are in the encoded string, not the length of the resulting string. The following bytes are then interpreted as bytes encoding characters in the UTF-8 format 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

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

Throws: IOException

if an I/O error occurs.

Throws: UTFDataFormatException

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

See Also:

readUnsignedShort

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