J2Me学习输入流DataInputStream

java.io
Class DataInputStream

java.lang.Object
  extended byjava.io.InputStream
      extended byjava.io.DataInputStream

All Implemented Interfaces:
    DataInput

public class DataInputStream
extends InputStream
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.

Since:
    JDK1.0, CLDC 1.0
See Also:
    DataOutputStream

Field Summary
protected  InputStream in
          The input stream.

Constructor Summary
DataInputStream(InputStream in)
          Creates a DataInputStream and saves its argument, the input stream in, for later use.

Method Summary
int available()
          Returns the number of bytes that can be read from this input stream without blocking.
void close()
          Closes this input stream and releases any system resources associated with the stream.
void mark(int readlimit)
          Marks the current position in this input stream.
boolean markSupported()
          Tests if this input stream supports the mark and reset methods.
int read()
          Reads the next byte of data from this input stream.
int read(byte[] b)
          See the general contract of the read method of DataInput.
int read(byte[] b, int off, int len)
          Reads up to len bytes of data from this 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.
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.
void reset()
          Repositions this stream to the position at the time the mark method was last called on this input stream.
long skip(long n)
          Skips over and discards n bytes of data from the input stream.
int skipBytes(int n)
          See the general contract of the skipBytes method of DataInput.

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait


Field Detail
in

protected InputStream in

    The input stream.

Constructor Detail
DataInputStream

public DataInputStream(InputStream in)

    Creates a DataInputStream and saves its argument, the input stream in, for later use.

Parameters:
    in - the input stream.

Method Detail
read

public int read()
         throws IOException

    Reads the next byte of data from this 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.

    This method simply performs in.read() and returns the result.

    Specified by:
        read in class InputStream

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

read

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

    See the general contract of the read method of DataInput.

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

    Overrides:
        read in class InputStream

    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:
        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 this input stream into an array of bytes. This method blocks until some input is available.

    This method simply performs in.read(b, off, len) and returns the result.

    Overrides:
        read in class InputStream

    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:
        InputStream.read()

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.
    Since:
        CLDC 1.1
    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.
    Since:
        CLDC 1.1
    See Also:
        readLong(), Double.longBitsToDouble(long)

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.
    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 UTF-8 encoding of a Unicode string.
    See Also:
        readUnsignedShort()

skip

public long skip(long n)
          throws IOException

    Skips over and discards n bytes of data from the input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. The actual number of bytes skipped is returned.

    This method simply performs in.skip(n).

    Overrides:
        skip in class InputStream

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

available

public int available()
              throws IOException

    Returns the number of bytes that can be read from this input stream without blocking.

    This method simply performs in.available() and returns the result.

    Overrides:
        available in class InputStream

    Returns:
        the number of bytes that can be read from the input stream without blocking.
    Throws:
        IOException - if an I/O error occurs.

close

public void close()
           throws IOException

    Closes this input stream and releases any system resources associated with the stream. This method simply performs in.close().

    Overrides:
        close in class InputStream

    Throws:
        IOException - if an I/O error occurs.

mark

public void mark(int readlimit)

    Marks the current position in this input stream. A subsequent call to the reset method repositions this stream at the last marked position so that subsequent reads re-read the same bytes.

    The readlimit argument tells this input stream to allow that many bytes to be read before the mark position gets invalidated.

    This method simply performs in.mark(readlimit).

    Overrides:
        mark in class InputStream

    Parameters:
        readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.
    See Also:
        InputStream.reset()

reset

public void reset()
           throws IOException

    Repositions this stream to the position at the time the mark method was last called on this input stream.

    This method simply performs in.reset().

    Stream marks are intended to be used in situations where you need to read ahead a little to see what's in the stream. Often this is most easily done by invoking some general parser. If the stream is of the type handled by the parse, it just chugs along happily. If the stream is not of that type, the parser should toss an exception when it fails. If this happens within readlimit bytes, it allows the outer code to reset the stream and try another parser.

    Overrides:
        reset in class InputStream

    Throws:
        IOException - if the stream has not been marked or if the mark has been invalidated.
    See Also:
        InputStream.mark(int), IOException

markSupported

public boolean markSupported()

    Tests if this input stream supports the mark and reset methods. This method simply performs in.markSupported().

    Overrides:
        markSupported in class InputStream

    Returns:
        true if this stream type supports the mark and reset method; false otherwise.
    See Also:
        InputStream.mark(int), InputStream.reset()