java programming: from problem analysis to program design, 3e chapter 6 graphical user interface...

Java Programming: From Problem Analysis to Program Design, 3e

Chapter 6

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

2Java Programming: From Problem Analysis to Program Design, 3e

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


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 (continued)

• 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 JFrame object• The class JFrame provides various

methods to control attributes of a window• Measured in pixels of height and width• Attributes associated with windows

– Title– Width– Height


class JFrame

• GUI window instance created as instance of JFrame

• Provides various methods to control window attributes


Methods Provided by the class JFrame


Methods Provided by the class Jframe (continued)


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– 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 JFrame


Methods Provided by the class Container


class JLabel

• Labels: objects of 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


class Jlabel (continued)


class JTextField

• Text fields: objects belonging to class JTextField

• To create text field– Declare reference variable of type JTextField

– Instantiate object


class JTextField (continued)


class JButton

• Provided to create buttons in Java

• To create button– Same technique as creating JLabel and JTextField


class Jbutton (continued)


Handling an Event

• Action event: event created when JButton is clicked

• Event listener: object that receives message when JButton is clicked

• In Java, you must register the listener


Handling an Event (continued)

• 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 Celsius

• Output: temperature in Celsius if input is Fahrenheit; temperature in Fahrenheit if input is Celsius


Programming Example: Temperature Conversion (continued)

• 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 methodology1. 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

• An inoperable candy machine has a cash register and four dispensers to hold and release items sold by the machine

• The machine sells: candies, chips, gum, and cookies

• Write a program for this candy machine so that it can be put into operation


Object-Oriented Design Example 2 (continued)

• 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


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 Integer


The class Integer (continued)



Integer num; num = new Integer(86)



int x; Integer num;

num = 25;

For the most part, this statement is similar to the statement:

num = new Integer(25);

The expression:

num = 25;

is referred to as autoboxing of the int type



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



• 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 equals


Chapter Summary• Every GUI contains a window• Various components are added to content pane of

window• class JFrame 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


Chapter Summary (continued)• Action listener must have method called actionPerformed

• 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

java programming: from problem analysis to program design, 3e chapter 6 graphical user interface...

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