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

Chapter Objectives Learn about basic GUI components Explore how the GUI components Frame, Label, Textile, and JButton work Become familiar with the concept of event- driven programming

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

Graphical User Interface (GUI) Components View inputs and outputs simultaneously One graphical window Input values in any order Change input values in window Click on buttons to get output

Java GUI Components

Graphical User Interface (GUI) Components GUI components placed in content pane GUI components –Windows –Labels –Text areas –Buttons

GUI Components Added to content pane of window Not added to window itself Pixel: picture element

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

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

Methods Provided by the class Frame

Two Ways to Create a Window First way –Declare object of type Frame –Instantiate object –Use various methods to manipulate window Second way –Create class containing application program by extending definition of class Frame –Utilizes mechanism of inheritance

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 Frame

Methods Provided by the class Container

class Label Labels: objects of particular class type class Label: used to create labels Label attributes –title –width –height To create a label –Instantiate object of type Label –Modify attributes to control display of labels

Methods Provided by the class Label

class Textile Text fields: objects belonging to class Textile To create text field –Declare reference variable of type Textile –Instantiate object

Methods Provided by the class Textile

class JButton Provided to create buttons in Java To create button –Same technique as creating Label and Textile

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

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 Nouns –Length, width, rectangle, perimeter, area

class Rectangle with Data Members and Operations

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 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 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

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