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JavaIO

Work out examples while studying for Java Professional Cert.

 

Some Learning Notes

Java I/O

  • A stream is a sequence of data.
  • The data source and data destination can be anything that holds, generates, or consumes data.
    It can be disk files, another program, a peripheral device, a network socket, or an array.

 

Byte Stream: InputStream, OutputStream

  • Top level: abstract class InputStream
    abstract int read() --> Reads the next byte
    int read (byte[] b) --> Reads some number of bytes from the input stream and stores them into the buffer array b.
  • Byte streams perform input and output of 8-bit bytes.
  • int read() will read the next byte, and convert it to an int (0-255), and return that int.
  • void close(): close() of InputStream class does nothing. The children override this method.
  • Top level: abstract class OutputStream
  • void write(int b): write a byte to output stream. the int is range 0-255.
  • void close(): close () of OutputStream does nothing. Its children override it.
  • void flush(): forces any buffered output bytes to be written out.
    flush() of OutputStream does nothing.
    Buffer children override it.

 

Byte Stream: FileInputStream, FileOutputStream

  • class FileInputStream extends InputStream
    It is file I/O byte stream
  • Read: returns the next byte it reads.
    The byte can be from 0 to 255.
    returns -1 if no byte is available / the end of the stream is reached.
    This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.
  • Blocking methods in Java are those methods which block the executing thread until their operation finished.
    A famous example of blocking method is InputStream read() method which blocks until all data from InputStream has been read completely.
  • class FileOutputStream extends OutputStream
  • Will create file if file does not exist.
    By default will override the file.
    If want to append only: use FileOutputStream(String name, boolean append) constructor.

 

Character Stream: Reader, Writer

  • Byte stream is low-level I/O. Byte streams should only be used for the most primitive I/O.
  • If a file contains character data, the best approach is to use character streams.
  • Unicode: a character is represented as a code point.
  • Unicode can be implemented by different character encodings.
  • UTF-8 is a popular one among them.
  • UTF-8 uses one byte for the first 128 code points, and up to 4 bytes for other characters.
  • The first 128 Unicode code points represent the ASCII characters, which means that any ASCII text is also a UTF-8 text.
  • Top level: abstract class Reader
  • Java uses Unicode. Reader and Writer can convert between Unicode and system encoding.
  • Some notable Readers: InputStreamReader, BufferedReader, FileReader(extends InputStreamReader)
  • Top level: abstract class Writer
  • Some notable Writers: OutputStreamWriter, BufferedWriter, FileWriter(extends OutputStreamWriter), PrintWriter

 

Character Stream: InputStreamReader, FileReader

  • InputStreamReader V.S FileReader:
    1. A FileReader is an InputStreamReader
    2. An InputStreamReader is a bridge from byte streams to character streams: It reads bytes and decodes them into characters using a specified charset. Therefore it can be constructed by passing in InputStream.
    3. FileReader is a convenience class for reading character files. It can be instantiated by passing in file name.
    4. InputStreamReader can handle all input streams, not just files.
  • Difference between InputStream.read() vs InputStreamReader.read():
    1. InputStream.read(): 165 reads; InputStreamReader.read(): 155 reads
    2. InputStream.read(): Chinese characters byte by byte; InputStreamReader.read(): Chinese characters character by character.

 

Character Streams that Use Byte Streams

  • Character streams are often "wrappers" for byte streams.
  • The character stream uses the byte stream to perform the physical I/O, while the character stream handles translation between characters and bytes.
  • FileReader, for example, uses FileInputStream, while FileWriter uses FileOutputStream.

 

Buffered Streams

  • A program can convert an unbuffered stream into a buffered stream using the wrapping idiom.
  • Can be used to support line-oriented I/O.

 

Path

  • A Path is not system independent, i.e., it is system dependent.
  • You cannot compare a Path from a Solaris file system and expect it to match a Path from a Windows file system.

 

 

Useful links