Chapter 6
Graphical User Interface (GUI) and
Object-Oriented Design (OOD)
class JButton


Provided to create buttons in Java
Used to create and modify JButton objects



To create button



Button may be labeled with a text string or an icon
May register a listener object to process button click
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
Methods Provided by the class JButton
Methods Provided by the class
JButton
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
button
the listener object for a particular
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
Rectangle Program:
Sample Run
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
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
Sample Run for TempConversion
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
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
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
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
class Rectangle with Data Members
and Operations
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 cookies—each
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.
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.
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 cookies—
each 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.
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.
Object-Oriented Design
Example 2
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
 Candy
4
on hand
Machine:
dispensers: name for item being held
 1 cash register
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 cookies—each
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.
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.
Object-Oriented Design
Example 2
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)
The class IntClass
The class IntClass
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
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