Java™ Platform
Standard Ed. 6

javax.imageio.stream
Interface ImageInputStream

All Superinterfaces:
DataInput
All Known Subinterfaces:
ImageOutputStream
All Known Implementing Classes:
FileCacheImageInputStream, FileCacheImageOutputStream, FileImageInputStream, FileImageOutputStream, ImageInputStreamImpl, ImageOutputStreamImpl, MemoryCacheImageInputStream, MemoryCacheImageOutputStream

public interface ImageInputStream
extends DataInput

A seekable input stream interface for use by ImageReaders. Various input sources, such as InputStreams and Files, as well as future fast I/O sources may be "wrapped" by a suitable implementation of this interface for use by the Image I/O API.

See Also:
ImageInputStreamImpl, FileImageInputStream, FileCacheImageInputStream, MemoryCacheImageInputStream

Method Summary
 void close()
          Closes the stream.
 void flush()
          Discards the initial position of the stream prior to the current stream position.
 void flushBefore(long pos)
          Discards the initial portion of the stream prior to the indicated postion.
 int getBitOffset()
          Returns the current bit offset, as an integer between 0 and 7, inclusive.
 ByteOrder getByteOrder()
          Returns the byte order with which data values will be read from this stream as an instance of the java.nio.ByteOrder enumeration.
 long getFlushedPosition()
          Returns the earliest position in the stream to which seeking may be performed.
 long getStreamPosition()
          Returns the current byte position of the stream.
 boolean isCached()
          Returns true if this ImageInputStream caches data itself in order to allow seeking backwards.
 boolean isCachedFile()
          Returns true if this ImageInputStream caches data itself in order to allow seeking backwards, and the cache is kept in a temporary file.
 boolean isCachedMemory()
          Returns true if this ImageInputStream caches data itself in order to allow seeking backwards, and the cache is kept in main memory.
 long length()
          Returns the total length of the stream, if known.
 void mark()
          Marks a position in the stream to be returned to by a subsequent call to reset.
 int read()
          Reads a single byte from the stream and returns it as an integer between 0 and 255.
 int read(byte[] b)
          Reads up to b.length bytes from the stream, and stores them into b starting at index 0.
 int read(byte[] b, int off, int len)
          Reads up to len bytes from the stream, and stores them into b starting at index off.
 int readBit()
          Reads a single bit from the stream and returns it as an int with the value 0 or 1.
 long readBits(int numBits)
          Reads a bitstring from the stream and returns it as a long, with the first bit read becoming the most significant bit of the output.
 boolean readBoolean()
          Reads a byte from the stream and returns a boolean value of true if it is nonzero, false if it is zero.
 byte readByte()
          Reads a byte from the stream and returns it as a byte value.
 void readBytes(IIOByteBuffer buf, int len)
          Reads up to len bytes from the stream, and modifies the supplied IIOByteBuffer to indicate the byte array, offset, and length where the data may be found.
 char readChar()
          Equivalent to readUnsignedShort, except that the result is returned using the char datatype.
 double readDouble()
          Reads 8 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as a double.
 float readFloat()
          Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as a float.
 void readFully(byte[] b)
          Reads b.length bytes from the stream, and stores them into b starting at index 0.
 void readFully(byte[] b, int off, int len)
          Reads len bytes from the stream, and stores them into b starting at index off.
 void readFully(char[] c, int off, int len)
          Reads len chars (unsigned 16-bit integers) from the stream according to the current byte order, and stores them into c starting at index off.
 void readFully(double[] d, int off, int len)
          Reads len doubles (64-bit IEEE double-precision floats) from the stream according to the current byte order, and stores them into d starting at index off.
 void readFully(float[] f, int off, int len)
          Reads len floats (32-bit IEEE single-precision floats) from the stream according to the current byte order, and stores them into f starting at index off.
 void readFully(int[] i, int off, int len)
          Reads len ints (signed 32-bit integers) from the stream according to the current byte order, and stores them into i starting at index off.
 void readFully(long[] l, int off, int len)
          Reads len longs (signed 64-bit integers) from the stream according to the current byte order, and stores them into l starting at index off.
 void readFully(short[] s, int off, int len)
          Reads len shorts (signed 16-bit integers) from the stream according to the current byte order, and stores them into s starting at index off.
 int readInt()
          Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as an int.
 String readLine()
          Reads the next line of text from the input stream.
 long readLong()
          Reads 8 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as a long.
 short readShort()
          Reads two bytes from the stream, and (conceptually) concatenates them according to the current byte order, and returns the result as a short value.
 int readUnsignedByte()
          Reads a byte from the stream, and (conceptually) converts it to an int, masks it with 0xff in order to strip off any sign-extension bits, and returns it as a byte value.
 long readUnsignedInt()
          Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order, converts the result to a long, masks it with 0xffffffffL in order to strip off any sign-extension bits, and returns the result as an unsigned long value.
 int readUnsignedShort()
          Reads two bytes from the stream, and (conceptually) concatenates them according to the current byte order, converts the resulting value to an int, masks it with 0xffff in order to strip off any sign-extension buts, and returns the result as an unsigned int value.
 String readUTF()
          Reads in a string that has been encoded using a modified UTF-8 format.
 void reset()
          Returns the stream pointer to its previous position, including the bit offset, at the time of the most recent unmatched call to mark.
 void seek(long pos)
          Sets the current stream position to the desired location.
 void setBitOffset(int bitOffset)
          Sets the bit offset to an integer between 0 and 7, inclusive.
 void setByteOrder(ByteOrder byteOrder)
          Sets the desired byte order for future reads of data values from this stream.
 int skipBytes(int n)
          Moves the stream position forward by a given number of bytes.
 long skipBytes(long n)
          Moves the stream position forward by a given number of bytes.
 

Method Detail

setByteOrder

void setByteOrder(ByteOrder byteOrder)
Sets the desired byte order for future reads of data values from this stream. For example, the sequence of bytes '0x01 0x02 0x03 0x04' if read as a 4-byte integer would have the value '0x01020304' using network byte order and the value '0x04030201' under the reverse byte order.

The enumeration class java.nio.ByteOrder is used to specify the byte order. A value of ByteOrder.BIG_ENDIAN specifies so-called big-endian or network byte order, in which the high-order byte comes first. Motorola and Sparc processors store data in this format, while Intel processors store data in the reverse ByteOrder.LITTLE_ENDIAN order.

The byte order has no effect on the results returned from the readBits method (or the value written by ImageOutputStream.writeBits).

Parameters:
byteOrder - one of ByteOrder.BIG_ENDIAN or java.nio.ByteOrder.LITTLE_ENDIAN, indicating whether network byte order or its reverse will be used for future reads.
See Also:
ByteOrder, getByteOrder(), readBits(int)

getByteOrder

ByteOrder getByteOrder()
Returns the byte order with which data values will be read from this stream as an instance of the java.nio.ByteOrder enumeration.

Returns:
one of ByteOrder.BIG_ENDIAN or ByteOrder.LITTLE_ENDIAN, indicating which byte order is being used.
See Also:
ByteOrder, setByteOrder(java.nio.ByteOrder)

read

int read()
         throws IOException
Reads a single byte from the stream and returns it as an integer between 0 and 255. If the end of the stream is reached, -1 is returned.

The bit offset within the stream is reset to zero before the read occurs.

Returns:
a byte value from the stream, as an int, or -1 to indicate EOF.
Throws:
IOException - if an I/O error occurs.

read

int read(byte[] b)
         throws IOException
Reads up to b.length bytes from the stream, and stores them into b starting at index 0. The number of bytes read is returned. If no bytes can be read because the end of the stream has been reached, -1 is returned.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
b - an array of bytes to be written to.
Returns:
the number of bytes actually read, or -1 to indicate EOF.
Throws:
NullPointerException - if b is null.
IOException - if an I/O error occurs.

read

int read(byte[] b,
         int off,
         int len)
         throws IOException
Reads up to len bytes from the stream, and stores them into b starting at index off. The number of bytes read is returned. If no bytes can be read because the end of the stream has been reached, -1 is returned.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
b - an array of bytes to be written to.
off - the starting position within b to write to.
len - the maximum number of bytes to read.
Returns:
the number of bytes actually read, or -1 to indicate EOF.
Throws:
NullPointerException - if b is null.
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than b.length.
IOException - if an I/O error occurs.

readBytes

void readBytes(IIOByteBuffer buf,
               int len)
               throws IOException
Reads up to len bytes from the stream, and modifies the supplied IIOByteBuffer to indicate the byte array, offset, and length where the data may be found. The caller should not attempt to modify the data found in the IIOByteBuffer.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
buf - an IIOByteBuffer object to be modified.
len - the maximum number of bytes to read.
Throws:
IndexOutOfBoundsException - if len is negative.
NullPointerException - if buf is null.
IOException - if an I/O error occurs.

readBoolean

boolean readBoolean()
                    throws IOException
Reads a byte from the stream and returns a boolean value of true if it is nonzero, false if it is zero.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readBoolean in interface DataInput
Returns:
a boolean value from the stream.
Throws:
EOFException - if the end of the stream is reached.
IOException - if an I/O error occurs.

readByte

byte readByte()
              throws IOException
Reads a byte from the stream and returns it as a byte value. Byte values between 0x00 and 0x7f represent integer values between 0 and 127. Values between 0x80 and 0xff represent negative values from -128 to /1.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readByte in interface DataInput
Returns:
a signed byte value from the stream.
Throws:
EOFException - if the end of the stream is reached.
IOException - if an I/O error occurs.

readUnsignedByte

int readUnsignedByte()
                     throws IOException
Reads a byte from the stream, and (conceptually) converts it to an int, masks it with 0xff in order to strip off any sign-extension bits, and returns it as a byte value.

Thus, byte values between 0x00 and 0x7f are simply returned as integer values between 0 and 127. Values between 0x80 and 0xff, which normally represent negative bytevalues, will be mapped into positive integers between 128 and 255.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readUnsignedByte in interface DataInput
Returns:
an unsigned byte value from the stream.
Throws:
EOFException - if the end of the stream is reached.
IOException - if an I/O error occurs.

readShort

short readShort()
                throws IOException
Reads two bytes from the stream, and (conceptually) concatenates them according to the current byte order, and returns the result as a short value.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readShort in interface DataInput
Returns:
a signed short value from the stream.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
getByteOrder()

readUnsignedShort

int readUnsignedShort()
                      throws IOException
Reads two bytes from the stream, and (conceptually) concatenates them according to the current byte order, converts the resulting value to an int, masks it with 0xffff in order to strip off any sign-extension buts, and returns the result as an unsigned int value.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readUnsignedShort in interface DataInput
Returns:
an unsigned short value from the stream, as an int.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
getByteOrder()

readChar

char readChar()
              throws IOException
Equivalent to readUnsignedShort, except that the result is returned using the char datatype.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readChar in interface DataInput
Returns:
an unsigned char value from the stream.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
readUnsignedShort()

readInt

int readInt()
            throws IOException
Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as an int.

The bit offset within the stream is ignored and treated as though it were zero.

Specified by:
readInt in interface DataInput
Returns:
a signed int value from the stream.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
getByteOrder()

readUnsignedInt

long readUnsignedInt()
                     throws IOException
Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order, converts the result to a long, masks it with 0xffffffffL in order to strip off any sign-extension bits, and returns the result as an unsigned long value.

The bit offset within the stream is reset to zero before the read occurs.

Returns:
an unsigned int value from the stream, as a long.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
getByteOrder()

readLong

long readLong()
              throws IOException
Reads 8 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as a long.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readLong in interface DataInput
Returns:
a signed long value from the stream.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
getByteOrder()

readFloat

float readFloat()
                throws IOException
Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as a float.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readFloat in interface DataInput
Returns:
a float value from the stream.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
getByteOrder()

readDouble

double readDouble()
                  throws IOException
Reads 8 bytes from the stream, and (conceptually) concatenates them according to the current byte order and returns the result as a double.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readDouble in interface DataInput
Returns:
a double value from the stream.
Throws:
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.
See Also:
getByteOrder()

readLine

String readLine()
                throws IOException
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 '\n' is encountered, it is discarded and reading ceases. If the character '\r' is encountered, it is discarded and, if the following byte converts to the character '\n', then that is discarded also; reading then ceases. If end of file is encountered before either of the characters '\n' and '\r' 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 \u0100, that is, (char)256.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readLine in interface DataInput
Returns:
a String containing a line of text from the stream.
Throws:
IOException - if an I/O error occurs.

readUTF

String readUTF()
               throws IOException
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 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 the manner of the readUnsignedShort method, using network byte order (regardless of the current byte order setting). 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 current byte order setting is ignored.

The bit offset within the stream is reset to zero before the read occurs.

Note: This method should not be used in the implementation of image formats that use standard UTF-8, because the modified UTF-8 used here is incompatible with standard UTF-8.

Specified by:
readUTF in interface DataInput
Returns:
a String read from the stream.
Throws:
EOFException - if this stream reaches the end before reading all the bytes.
UTFDataFormatException - if the bytes do not represent a valid modified UTF-8 encoding of a string.
IOException - if an I/O error occurs.

readFully

void readFully(byte[] b,
               int off,
               int len)
               throws IOException
Reads len bytes from the stream, and stores them into b starting at index off. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readFully in interface DataInput
Parameters:
b - an array of bytes to be written to.
off - the starting position within b to write to.
len - the maximum number of bytes to read.
Throws:
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than b.length.
NullPointerException - if b is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readFully

void readFully(byte[] b)
               throws IOException
Reads b.length bytes from the stream, and stores them into b starting at index 0. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:
readFully in interface DataInput
Parameters:
b - an array of bytes.
Throws:
NullPointerException - if b is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readFully

void readFully(short[] s,
               int off,
               int len)
               throws IOException
Reads len shorts (signed 16-bit integers) from the stream according to the current byte order, and stores them into s starting at index off. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
s - an array of shorts to be written to.
off - the starting position withinb to write to.
len - the maximum number of shorts to read.
Throws:
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than s.length.
NullPointerException - if s is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readFully

void readFully(char[] c,
               int off,
               int len)
               throws IOException
Reads len chars (unsigned 16-bit integers) from the stream according to the current byte order, and stores them into c starting at index off. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
c - an array of chars to be written to.
off - the starting position withinb to write to.
len - the maximum number of chars to read.
Throws:
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than c.length.
NullPointerException - if c is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readFully

void readFully(int[] i,
               int off,
               int len)
               throws IOException
Reads len ints (signed 32-bit integers) from the stream according to the current byte order, and stores them into i starting at index off. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
i - an array of ints to be written to.
off - the starting position withinb to write to.
len - the maximum number of ints to read.
Throws:
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than i.length.
NullPointerException - if i is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readFully

void readFully(long[] l,
               int off,
               int len)
               throws IOException
Reads len longs (signed 64-bit integers) from the stream according to the current byte order, and stores them into l starting at index off. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
l - an array of longs to be written to.
off - the starting position withinb to write to.
len - the maximum number of longs to read.
Throws:
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than l.length.
NullPointerException - if l is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readFully

void readFully(float[] f,
               int off,
               int len)
               throws IOException
Reads len floats (32-bit IEEE single-precision floats) from the stream according to the current byte order, and stores them into f starting at index off. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
f - an array of floats to be written to.
off - the starting position withinb to write to.
len - the maximum number of floats to read.
Throws:
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than f.length.
NullPointerException - if f is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

readFully

void readFully(double[] d,
               int off,
               int len)
               throws IOException
Reads len doubles (64-bit IEEE double-precision floats) from the stream according to the current byte order, and stores them into d starting at index off. If the end of the stream is reached, an EOFException will be thrown.

The bit offset within the stream is reset to zero before the read occurs.

Parameters:
d - an array of doubles to be written to.
off - the starting position withinb to write to.
len - the maximum number of doubles to read.
Throws:
IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than d.length.
NullPointerException - if d is null.
EOFException - if the stream reaches the end before reading all the bytes.
IOException - if an I/O error occurs.

getStreamPosition

long getStreamPosition()
                       throws IOException
Returns the current byte position of the stream. The next read will take place starting at this offset.

Returns:
a long containing the position of the stream.
Throws:
IOException - if an I/O error occurs.

getBitOffset

int getBitOffset()
                 throws IOException
Returns the current bit offset, as an integer between 0 and 7, inclusive. The bit offset is updated implicitly by calls to the readBits method. A value of 0 indicates the most-significant bit, and a value of 7 indicates the least significant bit, of the byte being read.

The bit offset is set to 0 when a stream is first opened, and is reset to 0 by calls to seek, skipBytes, or any read or readFully method.

Returns:
an int containing the bit offset between 0 and 7, inclusive.
Throws:
IOException - if an I/O error occurs.
See Also:
setBitOffset(int)

setBitOffset

void setBitOffset(int bitOffset)
                  throws IOException
Sets the bit offset to an integer between 0 and 7, inclusive. The byte offset within the stream, as returned by getStreamPosition, is left unchanged. A value of 0 indicates the most-significant bit, and a value of 7 indicates the least significant bit, of the byte being read.

Parameters:
bitOffset - the desired offset, as an int between 0 and 7, inclusive.
Throws:
IllegalArgumentException - if bitOffset is not between 0 and 7, inclusive.
IOException - if an I/O error occurs.
See Also:
getBitOffset()

readBit

int readBit()
            throws IOException
Reads a single bit from the stream and returns it as an int with the value 0 or 1. The bit offset is advanced by one and reduced modulo 8.

Returns:
an int containing the value 0 or 1.
Throws:
EOFException - if the stream reaches the end before reading all the bits.
IOException - if an I/O error occurs.

readBits

long readBits(int numBits)
              throws IOException
Reads a bitstring from the stream and returns it as a long, with the first bit read becoming the most significant bit of the output. The read starts within the byte indicated by getStreamPosition, at the bit given by getBitOffset. The bit offset is advanced by numBits and reduced modulo 8.

The byte order of the stream has no effect on this method. The return value of this method is constructed as though the bits were read one at a time, and shifted into the right side of the return value, as shown by the following pseudo-code:

 long accum = 0L;
 for (int i = 0; i < numBits; i++) {
   accum <<= 1; // Shift left one bit to make room
   accum |= readBit();
 }
 
Note that the result of readBits(32) may thus not be equal to that of readInt() if a reverse network byte order is being used (i.e., getByteOrder() == false).

If the end of the stream is encountered before all the bits have been read, an EOFException is thrown.

Parameters:
numBits - the number of bits to read, as an int between 0 and 64, inclusive.
Returns:
the bitstring, as a long with the last bit read stored in the least significant bit.
Throws:
IllegalArgumentException - if numBits is not between 0 and 64, inclusive.
EOFException - if the stream reaches the end before reading all the bits.
IOException - if an I/O error occurs.

length

long length()
            throws IOException
Returns the total length of the stream, if known. Otherwise, -1 is returned.

Returns:
a long containing the length of the stream, if known, or else -1.
Throws:
IOException - if an I/O error occurs.

skipBytes

int skipBytes(int n)
              throws IOException
Moves the stream position forward by a given number of bytes. It is possible that this method will only be able to skip forward by a smaller number of bytes than requested, for example if the end of the stream is reached. In all cases, the actual number of bytes skipped is returned. The bit offset is set to zero prior to advancing the position.

Specified by:
skipBytes in interface DataInput
Parameters:
n - an int containing the number of bytes to be skipped.
Returns:
an int representing the number of bytes skipped.
Throws:
IOException - if an I/O error occurs.

skipBytes

long skipBytes(long n)
               throws IOException
Moves the stream position forward by a given number of bytes. This method is identical to skipBytes(int) except that it allows for a larger skip distance.

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

seek

void seek(long pos)
          throws IOException
Sets the current stream position to the desired location. The next read will occur at this location. The bit offset is set to 0.

An IndexOutOfBoundsException will be thrown if pos is smaller than the flushed position (as returned by getflushedPosition).

It is legal to seek past the end of the file; an EOFException will be thrown only if a read is performed.

Parameters:
pos - a long containing the desired file pointer position.
Throws:
IndexOutOfBoundsException - if pos is smaller than the flushed position.
IOException - if any other I/O error occurs.

mark

void mark()
Marks a position in the stream to be returned to by a subsequent call to reset. Unlike a standard InputStream, all ImageInputStreams support marking. Additionally, calls to mark and reset may be nested arbitrarily.

Unlike the mark methods declared by the Reader and InputStream interfaces, no readLimit parameter is used. An arbitrary amount of data may be read following the call to mark.

The bit position used by the readBits method is saved and restored by each pair of calls to mark and reset.

Note that it is valid for an ImageReader to call flushBefore as part of a read operation. Therefore, if an application calls mark prior to passing that stream to an ImageReader, the application should not assume that the marked position will remain valid after the read operation has completed.


reset

void reset()
           throws IOException
Returns the stream pointer to its previous position, including the bit offset, at the time of the most recent unmatched call to mark.

Calls to reset without a corresponding call to mark have no effect.

An IOException will be thrown if the previous marked position lies in the discarded portion of the stream.

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

flushBefore

void flushBefore(long pos)
                 throws IOException
Discards the initial portion of the stream prior to the indicated postion. Attempting to seek to an offset within the flushed portion of the stream will result in an IndexOutOfBoundsException.

Calling flushBefore may allow classes implementing this interface to free up resources such as memory or disk space that are being used to store data from the stream.

Parameters:
pos - a long containing the length of the stream prefix that may be flushed.
Throws:
IndexOutOfBoundsException - if pos lies in the flushed portion of the stream or past the current stream position.
IOException - if an I/O error occurs.

flush

void flush()
           throws IOException
Discards the initial position of the stream prior to the current stream position. Equivalent to flushBefore(getStreamPosition()).

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

getFlushedPosition

long getFlushedPosition()
Returns the earliest position in the stream to which seeking may be performed. The returned value will be the maximum of all values passed into previous calls to flushBefore.

Returns:
the earliest legal position for seeking, as a long.

isCached

boolean isCached()
Returns true if this ImageInputStream caches data itself in order to allow seeking backwards. Applications may consult this in order to decide how frequently, or whether, to flush in order to conserve cache resources.

Returns:
true if this ImageInputStream caches data.
See Also:
isCachedMemory(), isCachedFile()

isCachedMemory

boolean isCachedMemory()
Returns true if this ImageInputStream caches data itself in order to allow seeking backwards, and the cache is kept in main memory. Applications may consult this in order to decide how frequently, or whether, to flush in order to conserve cache resources.

Returns:
true if this ImageInputStream caches data in main memory.
See Also:
isCached(), isCachedFile()

isCachedFile

boolean isCachedFile()
Returns true if this ImageInputStream caches data itself in order to allow seeking backwards, and the cache is kept in a temporary file. Applications may consult this in order to decide how frequently, or whether, to flush in order to conserve cache resources.

Returns:
true if this ImageInputStream caches data in a temporary file.
See Also:
isCached(), isCachedMemory()

close

void close()
           throws IOException
Closes the stream. Attempts to access a stream that has been closed may result in IOExceptions or incorrect behavior. Calling this method may allow classes implementing this interface to release resources associated with the stream such as memory, disk space, or file descriptors.

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

Java™ Platform
Standard Ed. 6

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For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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