Java GUI

1
Java GUI

2
Graphical User Interface (GUI)
a text field
a label
a button
checkbox
combo box
a list
3
Graphical User Interfaces

• GUIs, AWT, and Swing
• AWT (Abstract Window Toolkit) is the original
  Java classes used for GUI development.
• Java 2 includes an improved toolkit, named Swing,
  to improve on AWT.
• Swing components are easier to use, more
  portable, and provide more functionality than
  older AWT components.

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Inheritance Helps

• Since Swing was designed as an improvement of
  AWT, it made sense not to start from scratch when
  designing the Swing components.
• To differentiate them, Swing components have
  names that begin with the letter J.

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Graphical User Interfaces

• GUIs and the Java Swing components
• JComponent is the ancestor of many Swing classes.
  Here are some descendants of the Jcomponent
  class.
• JButton
• JPanel
• JLabel
• JTextArea

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Windows

• We will use the class JFrame to create GUI
  windows.
• javax.swing.JFrame inherits from java.awt.Frame
• Every JFrame object has a content pane
  associated with it.
• Content panes are of type java.awt.Container

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What to Import

• When we design GUI programs, there are three
  packages we will need to import
• java.awt.
• java.awt.event.
• javax.swing.
• The java.awt.event package provides us with the
  capability to respond to user interface events,
  such as the pushing of a button.

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Displaying a Window

• The most common form of a window displayed via
  Swing is a JFrame.
• Next, we will see several example programs that
  will
• display JFrames
• place Swing objects in frames
• Exhibit event-driven programming
• Listeners will be used to respond to mouse
  events.

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Example GUIone

• Creating a JFrame
• new JFrame()
• Setting the size of our frame.
• setSize()
• Displaying the frame
• setVisible(true)

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FirstFrame.java
import javax.swing. class FirstFrame extends
JFrame public FirstFrame()
super("FirstFrame") setSize(300, 200)
setVisible(true) public static
void main(String args) JFrame frame new
FirstFrame() frame.setDefaultCloseOperation
(JFrame.EXIT_ON_CLOSE)
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Putting content in a GUI

• Frames constitute GUI real estate
• Organization of space
• Via other containers
• Each container defines and manages an area within
  the GUI
• e.g. menu bars, scroll bars, tool bars, panels,
  etc.
• Containers can be nested
• Individual components added into those Containers
  
• Containers may decide on their layout (will be
  discussed later)

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LabelTest

• import javax.swing.
• import java.awt.
• public class LabelTest extends JFrame
• public LabelTest()
• setTitle("Label Test")
• JLabel helloLabel new JLabel("Hello")
• add( helloLabel)
• setSize(300, 200)
• setVisible(true)
• public static void main(String args)
• LabelTest t new LabelTest()
• t.setDefaultCloseOperation(JFrame.EXIT_ON_CL
  OSE)

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Event Handling

• Perform some functionalities when the button is
  press
• Need to have a class that implements
  ActionListener
• The functionalities needed to perform will be put
  in the actionPerformed method
• Create an instance of this type of ActionListener
  
• Register the handler with the component

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ButtonTest

• public class ButtonTest extends JFrame
• public ButtonTest()
• setTitle("Button Test")
• JButton helloButton new JButton("Hello")
• add( helloButton)
• // create an instance of inner class
  ButtonHandler to use for button event handling
• ButtonHandler handler new
  ButtonHandler()
• //register the handler
• helloButton.addActionListener( handler )
• setSize(300, 200)
• setVisible(true)
• // inner class for button event handling
• private class ButtonHandler implements
  ActionListener
• // handle button event
• public void actionPerformed( ActionEvent
  event )

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No inner class

• public class ButtonTest2 extends JFrame
  implements ActionListener
• public ButtonTest2()
• setTitle("Button Test")
• JButton helloButton new JButton("Hello")
• add( helloButton)
• helloButton.addActionListener( this )
  //register the handler (the frame itself)
• setSize(300, 200)
• setVisible(true)
• // handle button event
• public void actionPerformed( ActionEvent
  event )
• JOptionPane.showMessageDialog( null,
• "You pressed " event.getActionComma
  nd() )