Java input output package

Java input output package

• 1.
  java.io Package Sujit Kumar ZenolocityLLC Copyright 2012-2024 @
• 2.
  java.io Package • Thejava.io package contains a fairly large number of classes that deal with Java input & output. Most of the classes consist of: • Byte streams : that are subclasses of the abstract classes InputStream or OutputStream • Character streams : that are subclasses of the abstract classes Reader and Writer • The methods for reading & writing data from byte streams and character streams are similar.
• 3.
  java.io Package (contd…) •The Reader and Writer classes read and write 16-bit Unicode characters. • The InputStream and OutputStream classes read and write 8-bit bytes respectively. • Derived classes of the above 4 abstract classes add additional responsibilities using the Decorator pattern.
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  How to choosethe correct implementation (derived class)? • • • • What is your format: text or binary ? Do you want random access to a file ? Are you using objects or non-objects ? What are your sources and sinks of data (like sockets, files, strings or array of characters) ? • Do you need to use filtering techniques like buffering, checksumming ?
• 5.
  Byte Stream AbstractClasses InputStream — byte reader • • • • read() a single byte or an array of bytes skip() bytes mark() and reset() position close() the stream (always in finally block) OutputStream —byte writer • write() a single byte or an array of bytes • flush() the stream (in case it is buffered) • close() the stream (always in finally block)
• 6.
  Character Stream AbstractClasses Reader — character reader • • • • read() a single char or into a char array skip() chars mark() and reset() position close() the stream (always in finally block) Writer — character writer • write() a single char or from a char array • flush() the stream (in case it is buffered) • close() the stream (always in finally block)
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  Byte Stream Concreteclasses • • • • • • • • FileInputStream, FileOutputStream BufferedInputStream, BufferedOutputStream ByteArrayInputStream, ByteArrayOutputStream DataInputStream, DataOutputStream FilterInputStream, FilterOutputStream ObjectInputStream, ObjectOutputStream PipedInputStream, PipedOutputStream LineNumberInputStream • PrintStream
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  Character Stream Concreteclasses • • • • • • • • FileReader, FileWriter BufferedReader, BufferedWriter CharArrayReader, CharArrayWriter InputStreamReader, InputStreamWriter FilterReader, FilterWriter ObjectReader, ObjectWriter PipedReader, PipedWriter StringReader, StringWriter • LineNumberReader • PrintWriter
• 9.
  Applying the DecoratorPattern • Example: Read each line from a file • BufferedReader => InputStreamReader => FileInputStream • Wrap an InputStreamReader over a FileInputStream. • Then, wrap a BufferedReader over the InputStreamReader.
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  Applying the DecoratorPattern (contd…) • BufferedReader => Reads text from a characterinput stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines. • FileInputStream => obtains input bytes from a file in a file system. • InputStreamReader => bridge from byte streams to character streams. It reads bytes and decodes them into characters using a specified charset.
• 11.
  Exception Handling • Theconstructors and methods of I/O classes can throw a checked exception. • The base class for I/O exceptions is java.io.IOException. Some methods can throw a subclass of IOException. For example, the constructors of FileInputStream, FileOutputStream and FileReader can throw FileNotFoundException. • The call to close() should always occur in a finally block (ensures that the I/O channel is closed properly even if an exception occurs).