Chapter 6: Graphical User Interface (GUI) and Object-Oriented Design (OOD)

1
Chapter 6 Graphical User Interface (GUI) and
Object-Oriented Design (OOD)

• Java Programming
• From Problem Analysis to Program Design,
• Second Edition

2
Chapter Objectives

• Learn about basic GUI components.
• Explore how the GUI components JFrame, JLabel,
  JTextField, and JButton work.
• Become familiar with the concept of event-driven
  programming.

3
Chapter Objectives

• Discover events and event handlers.
• Explore object-oriented design.
• Learn how to identify objects, classes, and
  members of a class.

4
Graphical User Interface (GUI) Components

• View inputs and outputs simultaneously.
• One graphical window.
• Input values in any order.
• Change input values in window.
• Click buttons to get output.

5
Java GUI Components
6
Graphical User Interface (GUI) Components

• GUI components placed in content pane.
• GUI components
• Windows
• Labels
• Text areas
• Buttons

7
GUI Components

• Added to content pane of window.
• Not added to window itself.
• Pixel A picture element.

8
Windows

• Can be created using a Frame object.
• The class Frame provides various methods to
  control attributes of a window.
• Measured in pixels of height and width.
• Attributes associated with windows
• Title
• Width
• Height

9
class JFrame

• GUI window instance created as instance of Frame.
• Provides various methods to control window
  attributes.

10
Methods Provided by the class JFrame
11
Methods Provided by the class JFrame
12
Two Ways to Create a Window

• First way
• Declare object of type JFrame.
• Instantiate object.
• Use various methods to manipulate window.
• Second way
• Create class-containing application program by
  extending definition of class JFrame.
• Utilize mechanism of inheritance.

13
Content Pane

• Inner area of GUI window (below title bar, inside
  border).
• To access content pane
• Declare reference variable of type Container.
• Use method getContentPane of class JFrame.

14
Methods Provided by the class Container
15
class JLabel

• Labels Objects of a particular class type.
• class JLabel Used to create labels.
• Label attributes
• Title
• Width
• Height
• To create a label
• Instantiate object of type JLabel.
• Modify attributes to control display of labels.

16
Methods Provided by the class JLabel
17
Methods Provided by the class JLabel
18
class JTextField

• Text fields Objects belonging to class
  JTextField.
• To create a text field
• Declare reference variable of type JTextField.
• Instantiate object.

19
Methods Provided by the class JTextField
20
class JButton

• Provided to create buttons in Java.
• To create a button
• Use the same technique that is used to create
  JLabel and JTextField.

21
Methods Provided by the class JButton
22
Methods Provided by the class JButton
23
Handling an Event

• Action event An event created when JButton is
  clicked.
• Event listener An object that receives a message
  when JButton is clicked.
• In Java, you must register the listener.

24
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 the actionPerformed method.

25
Rectangle Program Sample Run
26
Programming Example Temperature Conversion

• Input Temperature in Fahrenheit or Celsius.
• Output Temperature in Celsius if input is
  Fahrenheit temperature in Fahrenheit if input is
  Celsius.

27
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.

28
Sample Run for TempConversion
29
Object-Oriented Design

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

30
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.
• Nouns
• Length, width, rectangle, perimeter, area.

31
class Rectangle with Data Members and Operations
32
Object-Oriented Design Example 2

• A place to buy candy is 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 of which is 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.

33
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.

34
Object-Oriented Design Example 2
35
Object-Oriented Design Example 2
36
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).

37
The class Integer
38
The class Integer
39
The class Integer
Integer num num new Integer(86)
40
The class Integer
int x Integer num num 25
This statement is equivalent to the statement
num new Integer(25) The expression
num 25 is referred to as autoboxing of the
int type.
41
The class Integer
int x Integer num The
statement x num This statement is
equivalent to the statement x num.intValue()
This statement is referred to as auto
unboxing of the int type.
42
The class Integer

• To compare the values of two Integer objects, you
  can use the method compareTo.
• If you want to compare the values of two Integer
  objects only for equality, then you can use the
  method equal.

43
The class IntClass
44
The class IntClass
45
Chapter Summary

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

46
Chapter Summary

• A class is a collection of data members and
  methods associated with those members.
• Object-oriented design (OOD)
• Starts with a problem statement.
• Identifies required classes with nouns in problem
  statement.
• Identifies required methods with verbs in problem
  statement.