Abstract Windows Toolkit for Computer Science and MCA students

Write a note on Event Delegation Model.

• The event model is based on the Event Source and Event Listeners.
• Event Listener is an object that receives the messages / events. The Event Source is any object which creates the message / event.
• The Event Delegation model is based on - The Event Classes, The Event Listeners, Event Objects.
There are three participants in event delegation model in Java:

1. Event Source : the class which broadcasts the events.
2. Event Listeners : the classes which receive notifications of events.
3. Event Object : the class object which describes the event.
• An event occurs (like mouse click, key press, etc) which is followed by the event is broadcasted by the event source by invoking an agreed method on all event listeners.
• The event object is passed as argument to the agreed-upon method. Later the event listeners respond as they fit, like submit a form, displaying a message / alert etc.

• Event-delegation model allows a separation between a component's design and its use as it enables event handling to be handled by objects other than the ones that generate the events.
• As event-delegation model does not have to repeatedly process unhandled events, it performs much better in applications where many events are generated. This is unlike the event inheritance model.

Write a note on Layout Managers.

• A layout manager organizes the objects in a container.
• Layout manager is an object that is used to implement an interface which determines the size and position of the component that is used inside a container.
• Components can provide the size and the alignments regarding the container's layout.

• It has five areas for holding components: north, east, west, south and center.
• When there are only 5 elements to be placed, border layout is the right choice.

• Default layout manager.
• It lays out the components from left to right.

• Different components at different times are laid out.
• Controlled by a combo box, determining which panel the Card layout displays.

• A group of components are laid out I equal size and displays them in certain rows and columns.

• Flexible layout for placing components within a grid of cells
• Allows certain components to span more than one cell.
• The rows of the grid are not of the same height and height.