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Graphical User Interfaces

By: Abu Bakar. Graphical User Interfaces. GUI. What is GUI Support for GUI in java Java.awt package Javax.swing package GUI classes vs. Non-GUI Support Classes JButton, JFrame & JRadioButton etc Layout managers & Event handling classes etc. java.awt package. Abstract Windowing Toolkit

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Graphical User Interfaces

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  1. By: Abu Bakar Graphical User Interfaces

  2. GUI • What is GUI • Support for GUI in java • Java.awt package • Javax.swing package • GUI classes vs. Non-GUI Support Classes • JButton, JFrame & JRadioButton etc • Layout managers & Event handling classes etc

  3. java.awt package • Abstract Windowing Toolkit • tied directly to local platform’s GUI capabilities • often called Heavy Weight Components

  4. javax.swing package • Swing components are written, manipulated and displayed completely in java • allow the programmer to specify a uniform look and feel across all platforms • often referred to as Light Weight Components

  5. Class Hierarchy

  6. GUI Creation Steps • import required packages • import java.awt.* and/or javax.swing.* package • Setup the top level containers • allows other components to be nested inside it • Methods: add and setLayout • classified into two broad categories • Top Level containers  JFrame, Dialog and Applet etc • General Purpose Containers  JPanel, Toolbar and ScrollPane etc

  7. GUI Creation Steps –Cont.. • JFrameframe = new JFrame(); • Get the component area of the top level container • JFrameis a frame is a window. So, it can be interpreted as JFrameis a window • Every window has two areas. System Area & Component Area • The programmer cannot add/remove components to the System Area • Conntainercon = frame.getContentPane();

  8. GUI Creation Steps - Cont.. • Apply layout to component area • The layout of components in a container is usually governed by Layout Managers. • con.setLayout( new FlowLayout( ) ); • We can also write: FlowLayout layout = new FlowLayout(); con.setLayout(layout);

  9. GUI Creation Steps - Cont.. • Create and Add components • JTextField tf = new JTextField(10); • JButton button = new JButton (“My Button”); • c.add(tf); • con.add(button);

  10. GUI Creation Steps - Cont.. • Set size of frame and make it visible • frame.setSize(200, 300) ; • frame.setVisible(true) ; • frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  11. Code it & Run

  12. Layout Managers 1. Flow Layout 2. Grid Layout 3. Border Layout 4. Box Layout 5. Card Layout 6. GridBag Layout and so on

  13. Flow Layout • Position components on line by line basis. Each time a line is filled, a new line is started. • c.setLayout( new FlowLayout( ) );

  14. Grid Layout • Splits the panel/window into a grid (cells) with given number of rows and columns • c.setLayout( new GridLayout( 3 , 2 ) );

  15. Border Layout • Divides the area into five regions. North, South, East, West and Center • c.setLayout( new BorderLayout( ); • c.add( b1 , BorderLayout.NORTH ); • c.add( b2 , BorderLayout.SOUTH );

  16. GUI Creation Approaches

  17. More Complex GUI • Try this one also:

  18. More Swing Components

  19. To do • Try different GUI components and see how they look • But, do not forget to follow those steps, taught at the start of the lecture • And also do not forget the basics of java, you have learnt so far.

  20. Questions

  21. Events • GUIs generate events when the user interacts with GUI. For example, • Clicking a button • Moving the mouse • Closing Window etc

  22. Events – cont.. • In java, events are represented by Objects • These objects tells us about event and its source. Examples are • ActionEvent (Clicking a button) • WindowEvent (Doing something with window e.g. closing , minimizing) • Both AWT and swing components (not all) generate events • java.awt.event.*; • javax.swing.event.*;

  23. Event Handling Model • Common for both AWT and Swing components • Event Delegation Model • Processing of an event is delegated to a particular object (handlers ) in the program • Publish-Subscribe • Separate UI code from program logic

  24. Event Handling Steps • For a programmer the event Handling is a three step process in terms of code • Step 1 • Create components which can generate events • Step 2 • Build component (objects) that can handle events (Event Handlers) • Step 3 • Register handlers with generators

  25. Event Handling Process [1]Event Generators • You have already seen alot of event generators • Buttons • Mouse • Key • Window etc • JButton b1 = new JButton(“Hello”); • Now b1 can generate events

  26. Event Handling Process [2]Event Handlers/ Event Listener • First Technique - By Implementing Listener Interfaces • Java defines interfaces for every event type • If a class needs to handle an event. It needs to implement the corresponding listener interface • To handle “ActionEvent” a class needs to implement “ActionListener” • To handle “KeyEvent” a class needs to implement “KeyListener” • To handle “MouseEvent” a class needs to implement “MouseListener”

  27. Example Listeners public interface ActionListener { public void actionPerformed(ActionEvent e); } public interface ItemListener { public void itemStateChanged(ItemEvent e); } public interface ComponentListener { public void componentHidden(ComponentEvent e); public void componentMoved(ComponentEvent e); public void componentResized(ComponentEvent e); public void componentShown(ComponentEvent e); }

  28. Event Handling Process [2]Event Handlers • By implementing an interface the class agrees to implement all the methods that are present in that interface. • Inside the method the class can do what ever it wants to do with that event • Event Generator and Event Handler can be the same or different classes

  29. Event Handling Process [2]Event Handlers • To handle events generated by Button. A class needs to implement ActionListener interface. public class Test implements ActionListener{ public void actionPerformed(ActionEvent ae){ // do something } }

  30. Event Handling Process [3]Registering Handler with Generator • The event generator is told about the object which can handle its events • Event Generators have a method add______Listener(________) • b1.addActionListener(objectOfTestClass)

  31. Let’s code it • Event Handling, a Simple Example

  32. Behind the Scenes • What’s happening Behind the Scenes • ??

  33. Event Handling Participants • Event Generator / Source • Swing and awt components • For example, JButton, JTextField, JFrame etc • Generates an event object • Registers listeners with itself

  34. Event Handling Participants -- cont • Event Object • Encapsulate information about event that occurred and the source of that event • For example, if you click a button, ActionEvent object is created

  35. Event Handling Participants -- cont • Event Listener/handler • Receives event objects when notified, then responds • Each event source can have multiple listeners registered on it • Conversely, a single listener can register with multiple event sources

  36. Event Handling Participants -- cont • JVM • Receives an event whenever one is generated • Looks for the listener/handler of that event • If exist, delegate it for processing • If not, discard it (event)

  37. Event Handling Diagram

  38. Try to code • Making Small Calculator

  39. Questions

  40. Handling Mouse Events • Mouse events can be trapped for any GUI component that inherit from Component class. For example, JPanel, JFrame & JButton etc. • To handle Mouse events, two types of listener interfaces are available • MouseMotionListener • MouseListener

  41. Handling Mouse Events – cont.. • MouseMotionListener • For processing mouse motion events • Mouse motion event is generated when mouse is moved or dragged public interface MouseMotionListener { public void mouseDragged (MouseEvent me); public void mouseMoved (MouseEvent me); }

  42. Handling Mouse Events – cont.. • MouseListener • For processing “interesting” mouse events • Mouse event is generated when mouse is • Pressed • Released • clicked (pressed & released without moving the cursor) • Enter (mouse cursor enters the bounds of component) • Exit (mouse cursor leaves the bounds of component)

  43. Handling Mouse Events – cont.. public interface MouseListener { public void mousePressed (MouseEvent me); public void mouseClicked (MouseEvent me); public void mouseReleased(MouseEventme); public void mouseEntered (MouseEvent me); public void mouseExited (MouseEvent me); }

  44. Steps forHandling Mouse Motion Events • Create mouse motion events generating components • JFrame myFrame = new JFrame(); • Create Event Handler • Implement MouseMotionListener Interface • Provide implementaion for the required method public void mouseMoved (MouseEvent e) { // write your code here } • What about remaining method?

  45. Steps forHandling Mouse Motion Events • Register event generator with event handler myFrame.addMouseMotionListener (this);

  46. Let’s code it • Handling mouse motion events, a Simple Example

  47. Questions

  48. Handling Window Events • To handle window events, need to implement interface “WindowListner”. • Interface “WindowListner” contains 7 methods • We require only one i.e. windowClosing • So have to provide definitions of all methods to make concrete class

  49. Interface WindowListener public interface WindowListener { public void windowActivated (WindowEvent we); public void windowClosed (WindowEvent we); public void windowClosing (WindowEvent we); public void windowDeactivated (WindowEvent we); public void windowDeiconified (WindowEvent we); public void windowIconified (WindowEvent we); public void windowOpened (WindowEvent we); }

  50. Let’s code it • Window Exit Handler, a Simple Example

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