Computer Programming 2

• Exception


  An event that occurs during the execution of a program that disrupts the normal flow of instructions
• Exception handling


  The process used to change the normal flow of code execution if a specified exception occurs

  
• Checked exceptions


  • ClassNotFoundException
  • IllegalAccessException
  • InstantiationException
  • NoSuchMethodException
• Unchecked (runtime) exceptions


  • ArithmeticException
  • ArrayIndexOutOfBoundsException
  • ArrayStoreException
  • InputMismatchException
  • NullPointerException
  • NumberFormatException
  • StringIndexOutOfBoundsException
• try block


  A block of code that might throw an exception that can be handled by a matching catch block
• catch block


  A segment of code that can handle an exception that might be thrown by the try block that precedes it
• The getMessage() method can be used to determine Java's message about the exception

  
• Only one (1) try block is accepted in a program but there can be multiple catch blocks
• User-defined exception


  Created by extending the Exception class

  
• finally block


  Contains statements which are executed whether or not an exception is thrown
• There can only be one (1) finally block after a try-catch structure but it is not required
• A throw statement sends an exception out of a block or a method so it can be handled elsewhere
• Volatile storage


  Temporary. Volatile values (stored in variables) are lost when the computer loses its power. The Random Access Memory (RAM) is being used when a Java program stores a value in a variable.
• 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.
• Types of files

  • 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. The most common schemes are ASCII and Unicode. Examples are program files and application files.
• 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. Examples are images, music, and the .class extension files which are created after compiling Java programs.
• The common characteristics of a text file and binary file are size, name, and date and time of creation.
• Permanent files


  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.
• To verify if a file exists and if a program can access it when needed

  The checkAccess() method is used.
• Arguments of the checkAccess() method


  • None
  • READ
  • WRITE
  • EXECUTE
• To remove a file

  The delete() method of the Files class is used.
• Examples of exceptions that can be thrown when deleting a file: NoSuchFileException, DirectoryNotEmptyException, SecurityException, IOException.
• To remove a file without encountering an exception if the file does not exist

  The deleteIfExists() method can be used.
• 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. A character can be any letter, number, or other special symbol (such as punctuation mark) that makes up data.
• 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.