AWT Abstract Window Toolkit

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AWT(Abstract Window Toolkit)
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Container Classes
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Container Classes

• Window - This class defines a window with no
  title bar and no borders, not usually used by
  itself.
• Frame - Used as the basic Java application
  window.
• Has a title bar and provision for adding a menu.
  
• You can also add other components to it. You will
  usually sub-class this class to create a window
  class specific to your application.
• You can then draw in this window if you want to.

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Container Classes

• Dialog - Used to define a dialog for inputting
  data into a program.
• FileDialog - Defines a dialog designed
  specifically for selecting a file.
• Panel - Used as a container for other
  components. You cannot draw on a panel.
• Applet - This is the base class for a Java
  applet-a program designed to run embedded in a
  web page. All applets have this class as a base.
  You can draw in an Applet and add other
  components.

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Container Layout Managers
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Default Layout Managers

• Window - BorderLayout
• Frame - BorderLayout
• Dialog - BorderLayout
• FileDialog - BorderLayout
• Panel - FlowLayout
• Applet - FlowLayout

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Container bounds and inset values
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Components that are not Containers
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Canvas Class

• Most of these classes define simple user
  interface elements, but the Canvas class is a
  little bit different.
• You can use the Canvas class in two ways.
• Firstly, you can use it as a base class when you
  define your own components.
• Secondly you can draw on a Canvas object.
• The Canvas or Panel classes are usually extended
  for drawing applications.

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Component abstract class

• java.awt.Component is an abstract class that
  encapsulates the common functionality among AWT
  components.
• So much functionality is embedded in the
  Component class that it provides a whopping 120
  public methods.

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Component Attributes

• The Component class defines attributes which
  record the following information about an object
• position is stored as (x, y) coordinates in
  relation to its container.
• name of component stored as a String object
• size recorded as values for width height of
  object
• foreground background color that apply to the
  object

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More Component Attributes

• The font used by the object when text is
  displayed
• cursor for the object-defines the appearance of
  the cursor when it is over the object
• Whether the object is enabled or not-if the
  component is enabled it is active and can be
  accessed by the user
• Whether the object is visible on the screen or
  not-if an object is not marked as visible it is
  not drawn on the screen

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More Component Attributes

• Whether the object is 'valid' or not-
• if an object is not valid, layout of the entities
  that make up the object has not been determined.
• This is the case before an object is made
  visible.
• You can make a Container object invalid by
  changing its contents.
• It will then need to be validated

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java.awt.Component Properties Modifiable at
Runtime
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java.awt.Component Properties Modifiable at
Runtime cont.
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Size Position of Component
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Component Visual Characteristics

• The Look of a component is determined by two
  things
• representation of the component in the underlying
  operating system that Java uses when the
  component is displayed,
• and whatever you draw on the component.

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Drawing on Component Objects

• You can draw on a Component object by
  implementing its paint() method.
• The paint() method is called automatically when
  the component needs to be drawn, such as when
  your program requests that the area the component
  occupies should be redrawn, or the window
  containing the component is resized.

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Drawing on Component Objects

• Your implementation of the paint() method must
  include code to generate whatever you want drawn
  within the Component object.
• The component itself-the Button, Frame or
  whatever, will be drawn for you.
• You only need to override the paint() method for
  any additional stuff that you want to draw on it.

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Component Visual Characteristics
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Creating Cursors
The Cursor class contains a range of final static
constants that specify standard cursor types
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Using Containers

• You can find out about the components in a
  container object by using the following methods
  defined in the Container class

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Adding Components to a Container
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Adding a Menu to a Window

• A menu bar and menu items within it, are not
  components.
• Classes in the java.awt package that enable you
  to create a menu bar are based on the class
  MenuComponent derived from Object.

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Adding a Menu to a Window

• You can operate on menu items by using the
  following methods defined in the MenuItem class
• Since the Menu class is a sub-class of MenuItem,
  these methods also apply to Menu objects.

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Summary

• The package java.awt provides classes for
  creating a graphical user interface (GUI)
• A component is an object used to form part of the
  GUI for a program. All components have the
  class Component as a super-class
• A container is a component that can contain other
  components. A container object is created with a
  class that is a sub-class of Container. The
  classes Panel, Applet, Window, Frame, Dialog and
  FileDialog are containers.

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Summary cont.

• The class Applet is the base class for an applet.
  The Frame class is a base class for an
  application window with a title bar, borders
  and a menu
• Arrangement of components in a container
  controlled by a layout manager
• A menu bar is represented by a MenuBar object.
  Menu items can be objects of type Menu, of type
  MenuItem, or of type CheckboxMenuItem

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Looks Like Times Up!

• What so soon?