Chapter 16 Files and Streams 901 The DataInput (Web server type)
Chapter 16 Files and Streams 901 The DataInput interface is implemented by class DataInputStream and class RandomAccessFile (discussed later in the chapter); each needs to read primitive data types from a stream. DataInputStreams enable a program to read binary data from an InputStream. The DataInput interface includes methods read (for byte arrays), readBoolean, readByte, readChar, readDouble, readFloat, readFully (for byte arrays), readInt, readLong, readShort, readUnsignedByte, readUnsignedShort, readUTF (for strings) and skipBytes. The DataOutput interface is implemented by class DataOutputStream (a subclass of FilterOutputStream) and class RandomAccessFile; each needs to write primitive data types to an OutputStream. DataOutputStreams enable a program to write binary data to an OutputStream. The DataOutput interface includes methods flush, size, write (for a byte), write (for a byte array), writeBoolean, writeByte, writeBytes, writeChar, writeChars (for Unicode Strings), writeDouble, writeFloat, writeInt, writeLong, writeShort and writeUTF. Buffering is an I/O-performance-enhancement technique. With a BufferedOutputStream (a subclass of class FilterOutputStream), each output statement does not necessarily result in an actual physical transfer of data to the output device. Rather, each output operation is directed to a region in memory called a buffer that is large enough to hold the data of many output operations. Then, actual transfer to the output device is performed in one large physical output operation each time the buffer fills. The output operations directed to the output buffer in memory are often called logical output operations. With a BufferedOutputStream, a partially filled buffer can be forced out to the device at any time by invoking the stream object s flush method. Performance Tip 16.1 Since typical physical output operations are extremely slow compared to the speed of accessing computer memory, buffered outputs normally yield significant performance improvements over unbuffered outputs. With a BufferedInputStream (a subclass of class FilterInputStream), many logical chunks of data from a file are read as one large physical input operation into a memory buffer. As a program requests each new chunk of data, it is taken from the buffer (this is sometimes referred to as a logical input operation). When the buffer is empty, the next actual physical input operation from the input device is performed to read in the next group of logical chunks of data. Thus, the number of actual physical input operations is small compared with the number of read requests issued by the program. Performance Tip 16.2 Since typical input operations are extremely slow compared to the speed of accessing computer memory, buffered inputs normally yield significant performance improvements over unbuffered inputs. A PushbackInputStream (a subclass of class FilterInputStream) is for applications more exotic than those most programmers require. Essentially, the application reading a PushbackInputStream reads bytes from the stream and forms aggregates consisting of several bytes. Sometimes, to determine that one aggregate is complete, the application must read the first character past the end of the first aggregate. Once the program determines that the current aggregate is complete, the extra character is pushed
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