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

Chapter Objectives  Learn about classes used to build simple GUIs  Learn to use GUI components Frame, Label, Textile, and JButton  Become familiar with the concept of event-driven programming, events and event handlers  Explore object-oriented design using GUI as an one example  Learn how to identify objects, classes, and members of a class

Graphical User Interface (GUI) Components  We have already met JOptionPane from the swing library. It allowed us to use single variable text input boxes and information boxes  Now we will look at the basic components used to build User interfaces which allow us to:  view inputs and outputs simultaneously in a single window  To Input values of inputs in any order  To change input values in window  To click on buttons to initiate an action to produce an output

Java GUI Components

Graphical User Interface (GUI) Components  GUI components  Windows  Labels  Text areas  Buttons  A Window has a title, a content pane, additional GUI components can be placed on the content pane  Labels indicate what the contents of a text box is, what the purpose of a button is, etc.  A text area can be used to display and/or input data  Pushing a button is associated with an action or event

GUI Creation  First create a Window with a label indicating the purpose of the GUI. You can specify the size of the window in pixels.  Access the content pane of the window and choose the layout of the components  Add the desired GUI components (labels and text areas)  Add any buttons and handle the events associated with those buttons

Creating a Window  Create a Window by declaring an instance of a JFrame object, by using a constructor.  The class JFrame provides various methods to control attributes of a window  Attributes associated with window objects  Title  Width (measured in pixels)  Height (measured in pixels)

Methods Provided by the class Frame

Two Ways to Create a Window  First way  Declare object of type JFrame  Instantiate object  Use various methods to manipulate window  Second way  Create subclass of JFrame containing application program by extending definition of class JFrame. JFrame is a superclass of the new subclass  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  Class to create and modify JLabel objects (labels)  A label may be aligned left, center or right  A label may include text and/or an icon  To create a label  Declare and Instantiate object of type JLabel  May modify attributes to control display of labels  To add a label to a container (display the label in the content pane) use the method add from the container class

Methods Provided by the class JLabel

class JTextField  Used to create and modify JTextField objects belonging to class JTextField  Text field may accept input or display values  May specify length in characters of text field  To create text field  Declare reference variable of type JTextField  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 JTextField