EventDriven Programming and GUIs

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TOPIC 13
Window Interfaces Using Swing Objects

• Event-Driven Programming and GUIs
• Swing Basics and a Simple Demo Program
• Layout Managers
• Buttons and Action Listeners
• Container Classes
• Text I/O for GUIs
• Inner Classes

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Event-Driven Programming

• Programs with GUIs often use Event-Driven
  Programming
• Program waits for events to occur and then
  responds
• Examples of events
• Clicking a mouse button
• Dragging the mouse
• Pressing a key on the keyboard
• Firing an event when an object generates an
  event
• Listener object that waits for events to occur
• Event handler method that responds to an event

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A New Approach to Programming

• Previous Style of Programming
• List of instructions performed in order
• Next thing to happen is next thing in list
• Program performed by one agentthe computer

• Event-Driven Style of Programming
• Objects that can fire events and objects that
  react to events (listener objects)
• Next thing to happen depends on next event
• Program is interaction between user and computer

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Java GUI Components
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Graphical User Interface (GUI) Components

• GUI components
• Windows
• Labels
• Text areas
• Buttons
• GUI components placed in content pane
• Added to content pane of window
• Not added to window itself

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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

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class JFrame

• Provides various methods to control window
  attributes
• JFrame(String title)
• constructor for creating a JFrame with a title
• Container getContentPane()
• returns the content pane of the JFrame, which has
  the add method for adding components
• void setBackgroundColor(Color c)
• void setForegroundColor(Color c)
• void setSize(int width, int height)
• void setVisible(boolean b)
• void setTitle (String title)

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Methods Provided by the class JFrame
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Methods Provided by the class JFrame
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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

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Container class METHODS
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class JLabel

• Labels objects of particular class type
• Label attributes (i.e. every label has a )
• title
• width
• height
• To create a label
• Instantiate object of type JLabel
• Must be added to the pane
• Modify attributes to control display of labels

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Methods Provided by the class JLabel
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Methods Provided by the class JLabel
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• //Java program to create a window and place four
• // labels.
• import javax.swing.
• import java.awt.
• public class RectangleProgramTwo extends JFrame
• private static final int WIDTH 400
• private static final int HEIGHT 300
• private JLabel lengthL, widthL,
• areaL, perimeterL

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• public RectangleProgramTwo()
• setTitle("Area and Perimeter of a
  Rectangle")
• lengthL new JLabel("Enter the length,
  SwingConstants.RIGHT)
• widthL new JLabel("Enter the width ",
• SwingConstants.RIGHT)
• areaL new JLabel("Area ",
• SwingConstants.RIGHT)
• perimeterL new JLabel("Perimeter ",
• SwingConstants.RIGHT)
• Container pane getContentPane()
• pane.setLayout(new GridLayout(4,1))

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• pane.add(lengthL)
• pane.add(widthL)
• pane.add(areaL)
• pane.add(perimeterL)
• setSize(WIDTH, HEIGHT)
• setVisible(true)
• setDefaultCloseOperation(EXIT_ON_CLOSE)
• public static void main(String args)
• RectangleProgramTwo rectProg
• new RectangleProgramTwo()

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class JTextField

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

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Methods Provided by the class JTextField
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