GUI

1
GUI

• component buttons, menus, etc.
• event handling system
• containers to add controls to
• layout manager
• graphics operations
• controls press, scroll, choose between

2
procedure

• declare controls
• add controls to a container
• add an event handler

3
component

• javap java.awt.Component
• location
• size
• color
• etc.
• java foundation classes - more controls

4
container

• holds scrollbar, textfields, butons, etc
• must have their size set before they will show up
  on the screen
• setSize(500,100)

5
container

• Window basic free floating window that can be
  moved
• Panel nested in some larger container
• Frame subclass of Window with title and menubar

6
public class myFrame( static Frame fnew
Frame(myFrame) public static void main(
String a) f.setSize(300,100) f.show()

7
Layout in a Container

• setLayout( new FlowLayout() )
• FlowLayout components added left to right,
  keeping them centered, starting a new line when
  necessary
• you may specify LEFT or RIGHT justified instead
  of centered
• default for applet

8
Border Layout

• five components may be added
• they are positioned at north, east, south, west
  and center
• default for Frame

9
Grid Layout

• setLayout( new GridLayout(2,3))
• this makes two rows of three components
• all components are the same size
• GridBagLayout is a much more complicated version
  of GridLayout

10
mixing layouts

• create different containers
• set different layout managers in the different
  containers
• put the different containers into another
  container where you want them

11
controls

• Checkbox on or off control
• CheckboxGroup group of checkboxs
• Choice pop-up list
• Label string, left aligned
• List select from several alternatives
• TextField can enter a single line of chars
• TextArea several lines long

12
Checkbox
Checkbox cbnew Checkbox(small) add(cb) public
void init() cb.addItemListener(new
ItemListener() public void itemStateChanged(Ite
mEvent ie) System.out.println(ie.paramString())
)
13
Menu

• Frame f new Frame(Editor)
• MenuBar mbnew MenuBar()
• Menu file new Menu(file, true)
• //true is for tearoff menu

14
public void init() file.add(new
MenuItem(new)) file.add(new
MenuItem(open)) file.add(new
MenuItem(save)) file.add(new
MenuItem(-)) file.add(new MenuItem(exit))
mb.add(file) f.setSize(500,100) f.setMenuBar(
mb) f.show()
15
file.addActionListener( new ActionListener() pu
blic void actionPerformed(ActionEvent
e) System.out.println(field is
e.getActionCommand() ) )
16
convert applet to application

• make the top level class extend Frame, not Applet
• set the layout manager to FlowLayout
• add a main routine
• if the applet read parameters, have the main read
  command line arguments
• main should instantiate an object of the class

17
applet to application

• the constructor should call start() and init()
• add a menu with an Exit item or an exit button