Graphical User Interface (GUI) and Object-Oriented Design (OOD)

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Chapter 6

• Graphical User Interface (GUI) and
  Object-Oriented Design (OOD)

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class JButton

• Provided to create buttons in Java
• Used to create and modify JButton objects
• Button may be labeled with a text string or an
  icon
• May register a listener object to process button
  click
• To create button
• Declare reference variable of type JButton
• Instantiate object
• To add a text field to a container (display the
  label in the content pane) use the method add
  from the container class

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Methods Provided by the class JButton
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Methods Provided by the class JButton
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Handling an Event

• Action event event created when JButton is
  clicked
• Event listener object which receives message
  when JButton is clicked
• In Java, you must register the listener
• Specify the listener object for a particular
  button

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Handling an Event

• class ActionListener
• Handles action event
• Part of package java.awt.Event
• The class ActionListener is a special type of
  class (interface)
• Must contain actionPerformed method

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Rectangle Program Sample Run
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Programming Example Temperature Conversion

• Input temperature in Fahrenheit or Centigrade
• Output temperature in Centigrade if input is
  Fahrenheit temperature in Fahrenheit if input is
  Centigrade

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Programming Example Temperature Conversion

• Solution
• Create the appropriate JLabels, JTextFields,
  JButtons
• Add them to the created content pane
• Calculate the appropriate conversions when the
  buttons are clicked and an event is triggered

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Sample Run for TempConversion
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Object-Oriented Design

• Simplified methodology
• 1. Write down detailed description of problem
• 2. Identify all (relevant) nouns and verbs
• 3. From list of nouns, select objects
• 4. Identify data components of each object
• 5. From list of verbs, select operations

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Object-Oriented Design Example 1

• Problem Statement
• Write a program to input the length and width of
  a rectangle and calculate and print the perimeter
  and area of the rectangle
• Select Nouns
• Length, width, rectangle, perimeter, area
• Identify Classes
• Length, width, perimeter and area are properties
  of a rectangle
• Rectangle will be the class

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Object-Oriented Design Example 2

• Select essential attributes for the object of
  type Rectangle associated with the class
  Rectangle
• Length and width
• Perimeter and area are derived from length and
  width
• The data members of the class Rectangle are
  length and width
• Identify methods (operations) needed for the
  class Rectangle
• Extract the verbs from the problem statement
• Input, calculate, print
• List the required operations

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Object-Oriented Design Example 2

• Actions Input, calculate, print
• List the required operations
• Input setLength, setWidth
• Calculate computePerimeter, computeArea
• Print printArea, printPerimeter
• Access getLength, getWidth

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class Rectangle with Data Members and Operations
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Object-Oriented Design Example 1

• Candy may be bought from a candy machine. A
  new candy machine is bought for the gym, but it
  is not working properly. The candy machine has
  four dispensers to hold and release items sold by
  the candy machine and a cash register. The
  machine sells four products candies, chips, gum,
  and cookieseach stored in a separate dispenser.
  You have been asked to write a program for this
  candy machine so that it can be put into
  operation.

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Object-Oriented Design Example 2

• The program should do the following
• Show the customer the different products sold by
  the candy machine.
• Let the customer make the selection.
• Show the customer the cost of the item selected.
• Accept money from the customer.
• Return change.
• Release the item, that is, make the sale.

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Object-Oriented Design Example 3

• Candy may be bought from a candy machine. A
  new candy machine is bought for the gym, but it
  is not working properly. The candy machine has
  four dispensers to hold and release items sold by
  the candy machine and a cash register. The candy
  machine sells four products candies, chips, gum,
  and cookieseach stored in a separate dispenser.
  You have been asked to write a program for this
  candy machine so that it can be put into
  operation.

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Object-Oriented Design Example 4

• The program should do the following
• Show the customer the different products sold by
  the candy machine.
• Let the customer make the selection.
• Show the customer the cost of the item selected.
• Accept money from the customer.
• Return change.
• Release the item, that is, make the sale.

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Object-Oriented Design Example 2
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Identify Members of Each class

• Dispenser must contain at least one item to and
  that items cost to make the sale
• Number of items
• Cost of item
• Cash Register
• Cash on hand
• Candy Machine
• 4 dispensers name for item being held
• 1 cash register

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Object-Oriented Design Example 5

• Candy may be bought from a candy machine. A
  new candy machine is bought for the gym, but it
  is not working properly. The candy machine has
  four dispensers to hold and release items sold by
  the candy machine and a cash register. The
  machine sells four products candies, chips, gum,
  and cookieseach stored in a separate dispenser.
  You have been asked to write a program for this
  candy machine so that it can be put into
  operation.

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Object-Oriented Design Example 6

• The program should do the following
• Show the customer the different products sold by
  the candy machine.
• Let the customer make the selection.
• Show the customer the cost of the item selected.
• Accept money from the customer.
• Return change.
• Release the item, that is, make the sale.

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Object-Oriented Design Example 2
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Implementing Classes and Operations

• Algorithms are used to implement operations
• Construct and implement your own methods
• classes Integer, Double, Character, Long, Float
• Known as wrapper classes
• Provided so that values of primitive data types
  can be treated as objects
• Have limitations (cannot change value stored in
  objects)

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The class IntClass
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The class IntClass
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Chapter Summary

• Every GUI contains a window
• Various components are added to content pane of
  window
• class Frame is used to create windows
• Label is used to label GUI components and display
  information to user
• Textile is used for input/output
• JButton generates action event
• Action event is sent to action listener
• Action listener must have method called
  actionPerformed

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Chapter Summary

• class collection of data members and methods
  associated with those members
• Object-Oriented Design (OOD)
• Starts with a problem statement
• Identifies classes required with nouns in problem
  statement
• Identifies methods required with verbs in problem
  specification