Tuesday, 25 February 2014



Concept of window and advanced components in java

   The AWT defines windows according to a class hierarchy that adds functionality and specificity with each level. The two most common windows are those derived from Panel, which is used by applets, and those derived from Frame, which creates a standard window. Much of the functionality of these windows is derived from their parent classes.


         At the top of the AWT hierarchy is the Component class. Component is an abstract class that encapsulates all of the attributes of a visual component. All user interface elements that are displayed on the screen and that interact with the user are subclasses of Component. It defines over a hundred public methods that are responsible for managing events, such as mouse and keyboard input, positioning and sizing the window, and repainting. A Component object is responsible for remembering the current foreground and background colors and the currently selected text font.


     The Container class is a subclass of Component. It has additional methods that allow other Component objects to be nested within it. Other Container objects can be stored inside of a Container (since they are themselves instances of Component). This makes for a multileveled containment system. A container is responsible for laying out (that is, positioning) any components that it contains. 


     The Panel class is a concrete subclass of Container. It doesn’t add any new methods; it simply implements Container. Panel is the superclass for Applet. When screen output is directed to an applet, it is drawn on the surface of a Panel object. APanel is a window that does not contain a title bar, menu bar, or border. When you run an applet using an applet viewer, the applet viewer provides the title and border. Other components can be added to a Panel object by its add( ) method inherited from Container. Once these components have been added, you can position and resize them manually using the setLocation( ), setSize( ), or setBounds( ) methods defined by Component.


      The Window class creates a top-level window. A top-level window is not contained within any other object; it sits directly on the desktop. Generally, we don’t create

Window objects directly. Instead, we use a subclass of Window called Frame.


     Frame encapsulates what is commonly thought of as a “window.” It is a subclass of Window and has a title bar, menu bar, borders, and resizing corners. 


      It is not part of the hierarchy for applet or frame windows. Canvas encapsulates a blank window upon which you can draw. 

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