Comprog H1

• Types of Storage Device

  • Volatile storage
  • Non-volatile storage
• Volatile storage


  Temporary. Volatile values (stored in variables) are lost when the computer loses its power.
• Non-volatile storage


  Permanent. A Java program that is saved on a disk uses a non-volatile storage.
• Computer file


  A collection of data stored on a non-volatile device.
• Categories of File


  • Text file
  • Binary file
• Text file


  Consists of data that can be read in a text editor. Data in a text file is encoded using a scheme like ASCII or Unicode.
• Binary file


  Contains data that is not encoded as text. This file has contents in binary format, which means they cannot be understood by viewing them in a text editor.
• The common characteristics of a text file and binary file are size, name, and date and time of creation.
• Permanent files are commonly stored in the main directory or the root directory.
• Folders or directories


  Used to organize stored files.
• Path


  The complete list of the disk drive plus the hierarchy of directories in which the file is located.
• In the Windows operating system, the backslash (\) is the path delimiter – the special character used to separate path components.
• Path class


  Creates objects that contain information about files and directories, such as sizes, locations, creation dates, and is used to check whether a file or directory exists.
• Files class


  Performs operations on files and directories, such as determining their attributes, creating input and output streams, and deleting them.
• Absolute path


  A complete path; it does not require any other information to locate a file on a system.
• Relative path


  Depends on other path information.
• Path Methods


  • toString()
  • getFileName()
  • getNameCount()
  • getName(int)
• To convert a relative path to an absolute path, the toAbsolutePath() method is used.
• Arguments of the checkAccess() Method


  • None
  • READ
  • WRITE
  • EXECUTE
• The delete() method of the Files class accepts a Path parameter and removes the last element (file or directory) in a path or throws an exception if the deletion is unsuccessful.
• Examples of Exceptions


  • NoSuchFileException
  • DirectoryNotEmptyException
  • SecurityException
  • IOException
• The deleteIfExists() method can also be used to remove a file without encountering an exception if the file does not exist.
• To retrieve useful information about a file, the readAttributes() method of the Files class is used.
• BasicFileAttributes Methods


  • size()
  • creationTime()
  • lastModifiedTime()
  • compareTo()
• Character


  The smallest useful piece of data, which can be any letter, number, or other special symbol.
• Field


  A group of characters that has some meaning.
• Record


  A collection of fields that contain data about an entity.
• File


  Consists of related records.
• Sequential access file


  A data file where each record is accessed one after another in the order in which it was stored.
• Comma-separated values


  Values in a record that are separated by commas.
• Stream


  A flow of data. An input stream is data taken from a source (such as a file or the keyboard) and delivered into a program. An output stream is data delivered from a program to a destination (such as a file or the screen).
• Buffer


  A memory location into which you can write data, which you can read again later.
• Flushing


  Clears any bytes that have been sent to a buffer for output but have not yet been displayed on a hardware device.
• Input and Output Classes

  • InputStream
  • FileInputStream
  • BufferedInputStream
  • OutputStream
  • FileOutputStream
  • BufferedOutputStream
  • PrintStream
  • Reader
  • BufferedReader
  • BufferedWriter
• Common Methods of the OutputStream Class

  • close()
  • flush()
  • write(byte[] b)
  • write(byte[] b, int off, int len)
• StandardOpenOption Arguments


  • WRITE
  • APPEND
  • TRUNCATE_EXISTING
  • CREATE_NEW
  • CREATE
  • DELETE_ON_CLOSE
• The newInputStream() method of the Files class is used to open a file for reading.
• Common Methods of the BufferedReader Class

  • close()
  • read()
  • read(char[] buffer, int off, int len)
  • readLine()
  • skip(long n)
• BufferedWriter Methods


  • close()
  • flush()
  • newline()
  • write(String s, int off, int len)
  • write(char[] array, int off, int len)
  • write(int c)
• CAI - MGNDA