Introduction to Input and Output

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Introduction to Input and Output
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Layers (or Tiers) of an Application

• Software in the real world normally takes the
  form of a number of independent classes, like
  lego blocks, that can be stuck together in
  whatever form the designer wishes.
• Programmers thus write sections or components of
  a solution and put them together as they go along.

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Layers (or Tiers) of an Application

• The structure, where a solution is made out of
  connected classes, is called a layered or tiered
  approach.
• Distinct parts of a solution are organized into
  distinct groups and these are then put together
  to form layers.
• There are usually 3 distinct layers
• The user interface
• The logic layer
• The data layer

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Layer/ Tiers

• There are usually three distinct layers
• The user interface layer is intended to contain
  all the statements necessary to supply
  information to and obtain information from the
  user. The user interface layer may not
  necessarily process the information or store that
  information, for these functions it can pass the
  information to an application layer.
• The application layer, sometimes called the
  business logic or logic layer, is usually
  responsible for managing the information and
  performing operations on it, for example
  retrieving information, computing results,
  applying rules.
• The data layers responsibility is to store or
  retrieve the data on disk, in memory or in a
  database.

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Tier Example - Bank

• For example imagine that you were asked to write
  an Information System for a bank.
• The structure for a bank you meet the teller
  when you go in the door, they take your
  particular request and then defer to a manager.
  The manager then looks up your file to see if you
  can be granted your request, passes their
  decision to the teller who will notify you.

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Tier Example - Bank

• To computerise this would require a User
  Interface to the system that the tellers could
  use to create new accounts and to lodge and
  withdraw money from accounts. This User Interface
  would use another part of the program which would
  manage accounts. The layer which manages accounts
  would effectively replace the manager and
  therefore carries out business logic. Account
  information could be stored as objects in the
  data layer.
• Therefore we have three distinct sections for our
  problem, a Graphical User Interface layer, a
  Business Logic layer and a Data layer.

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Bank
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Developing Layers

• Each layer must be debugged before use
• Layers should be as independent as possible

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Layers
GUI
Enter Data
Login User
Handle data input
Logic
Data
DataBase
Account Manager
Account Object
Account Object
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Scenario

• We want to write a file to maintain an array of
  person objects.
• The user can add to, delete from or modify Person
  objects in the array.
• To make this practical, we must save data to a
  file
• If data was saved to a file then the program can
  read them back from the file and rebuild the array

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File I/O

• The most basic of Input/Output with Java is done
  with streams.
• Think of a stream as a flow of data, which can be
  an input stream or an output steam
• The stream commands enable you to write to a disk
  or to the output screen.

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File I/O

• A common term in programming is persistence.
• How can you make data persist, or still be
  available, from one run of a program to the next?
• You have 2 main choices-
• Write/Read from files
• Write/Read from database

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File I/O

• No matter where the data is coming from or going
  to and no matter what type its type, the
  mechanism for sequentially reading and writing
  data are basically the same.

READING WRITING
open a stream open a stream
while more information while more information
read information write information
close the stream close the stream
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File and FileDialog Objects

• Suppose we want to read the contents of a file
  sample.data. Before we begin the actual operation
  of reading data from this file, we must create a
  File object (from the java.io package) and
  associate it to the file.
• We call the File constructor
• File inFile new File (sample.data)
• File inFile new File (c\\JavaProjects,
  xyz.data)

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File and FileDialog

• A file MUST be opened before performing any file
  access operation.
• Since the user can select a file from a directory
  different from the current directory, we should
  use directoryPath in creating a file object
• File inFile new File (directoryPath, filename)

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Streams

• A Stream is simply a sequence of data items,
  usually eight-bit bytes.
• Java has 2 types of streams
• An input stream
• An output stream
• An input stream has a source from where the data
  items come and an output stream has a destination
  to where the data items are going.
• To read/write data items from/to a file, we
  attach one of the Java input/output stream
  objects to the file.
• The basic classes for Java I/0 are
  FileInputStream and FileOutputStream