Cup 5: Abstract Window Toolkit

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Cup 5 Abstract Window Toolkit

• Special Topics Java

Dr. Tim Margush Department of Mathematics and
Computer Science The University of Akron
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Abstract

• Offers functions common to all window systems
• Functions are implemented by calling on native
  window system functions
• Adds an extra level of communication
• Windows and components take on the
  characteristics of the host system

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AWT Services

• Standard GUI Components
• Event handling system
• Container class
• Layout managers
• Basic graphic operations

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Component

• Root class for most display oriented objects
• Includes instance variables for location, size,
  color, font, etc.
• There are two basic types of components
• widgets (WIndows gaDGETS)
• containers (this is an abstract class)

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Component Attributes

• Position and size
• name
• foreground and background colors
• font

• cursor
• enabled
• visible
• valid

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Container

• Window - free floating object that can be
  positioned on the screen
• Panel - a container that must be placed inside
  another container
• Applet is derived from this class
• Frame - subclass of window that adds a title
  string and menu capability
• GUI application windows start here

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A Self-Centered Window

• Public class MeMyselfAndI
• final private static int WW500, WH300
• public static void main(String args)
• Frame w new Frame(Me)
• Dimension S w.getToolkit().getScreenSize()
• w.setBounds((S.width-WW)/2, (S.height-WH)/2,WW,W
  H)
• w.show()

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An Eventful Window

• public class ClosingWindow extends Frame
• ClosingWindow(String s)
• super(s)
• enableEvents(AWTEvent.WINDOW_EVENT_MASK)
• protected void processWindowEvent(WindowEvent e)
• if (e.getID()WindowEvent.WINDOW_CLOSING)
• dispose()
• System.exit(0)
• super.processWindowEvent(e)

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Filling Containers

• Container objects hold a list of Component
  objects
• int countComponents()
• Component getComponent(n),
• Components are added at runtime
• myContainer.add(aComponent)
• A LayoutManager controls the positioning of the
  Components

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Layout Manager

• An object that controls size and placement of
  components added to a container
• All containers have a default layout manager
• You may choose a specific manager by calling the
  setLayout method
• setLayout(layoutObject)

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Flow Layout

• aContainer.setLayout(new FlowLayout)
• aContainer.add(new Button(x))
• //add additional components
• Components are displayed left to right,
  additional rows are used as needed.
• Centered controls are the default but left and
  right alignment is possible
• new FlowLayout(FlowLayout.LEFT)

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Common Layout Managers

• Flow
• left to right, top to bottom
• Border
• north, south, east, west, center
• Card
• one on top of the other

• Grid
• rows and columns
• GridBag
• components occupy one or more grid cells

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Combining Layout Managers

• Each Container uses its own LayoutManager object
• Inner nested containers are arranged by the outer
  container's LayoutManager
• The contents of the inner containers are arranged
  by their respective LayoutManager

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What's on the Menu

• Menus are derived from MenuComponent
• MenuBar - attaches to a frame
• MenuItem - elements of a Menu
• Menu - pulldown MenuItem
• CheckboxMenuItem - checkable MenuItem
• setMenuBar(MenuBar) - a Frame method to set the
  active menu bar

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Menu Bar Items

• The MenuBar's add method adds a Menu object to
  the menubar
• You can also get, count, and remove Menus, and
  manipulate shortcuts
• A Menu also has an add method to add a MenuItem
  to the Menu
• sub menus are created by adding a Menu to a Menu

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MenuItems

• new MenuItem()
• new MenuItem(String)
• new menuItem(String, MenuShortcut)
• Constructors to create a MenuItem object with
  indicated caption or label
• MenuShortcut is another class that is used to
  associate a shortcut key with a MenuItem
• Important methods for a MenuItem
• setEnabled, setLabel, addActionListener

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Menu

• new Menu()
• new Menu(String)
• new Menu(String, boolean)
• 2nd argument true means this is a "tear-off" menu
  (if supported)
• Important methods
• add(MenuItem or String)
• addSeparator()

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Checkbox Menu Items

• new CheckboxMenuItem()
• new CheckboxMenuItem(String)
• new CheckboxMenuItem(String, boolean)
• the boolean specifies the initial state
• Important methods
• addItemListener, getState, setState