Zarbiff Implementation Design and Details

Introduction

Our packages are a nested directory structure. The main directory contains most of the user interface objects and the main program (Zarbiff.java). Some of the most important objects are:

Zarbiff The main program at which execution starts and the master control panel window.
GraphInterface The interface between the graph data structure and the rest of the program. This interface is what is made accessible to filters when their action method is called.
GraphDispatcher A layer of indirection between GraphInterface method calls and our actual implementation of the graph. This is used to intercept actions that should occur whenever certain changes are made to the graph. For example, Coordinates must be informed whenever a vertex is added or deleted.
GraphCanvas The main surface of a GraphWindow that displays the graph. Handles mouse clicks that alter the graph.
FilterLoader Responsable for loading all filters from disk. Holds all filters in a hash table so that the same filter is not loaded more than once.

Our object model:

Events

The AWT implements an event handling system for windows, menus, mouseclicks, keypresses, etc. You can probably learn more about the way this works than we know by reading any good Java AWT book once they become available.

Component type objects are placed in an event hierarchy. The Zarbiff frame is at the top. The Toolbar and GraphWindows are its children. The GraphCanvas and Scrollbars are children of the GraphWindow. Whenever some event occurs, the handleEvent method of the deepest child that the mouse was in (at least in X/windows) is called and passed and Event object describing the event. Typically handleEvent takes some special action and/or calles super.handleEvent to obtain the default behavior.

The default handleEvent takes key and mouse presses and calls keyDown, mouseUp, etc. and these methods may also be overridden. If a handleEvent method returns true then no further processing occurs for this event. If it returns false, this means that this object has not completed all actions that need to occur to process the event. In this case, the handleEvent method of the parent of the object is called. Example: If a 'd' key click occurs when the mouse is in the main surface of a window then GraphCanvas.keyDown is called. GraphCanvas only intercepts the 'p' key click, so it returns false. Then GraphWindow.handleEvent is called and it again returns false. Finally Zarbiff.handleEvent is called. It looks for 'd' in a table of defined keys and calls the appropriate filter if an action is defined for the 'd' key. A user's customized keys, menus, and control panel buttons are defined in the '.zarbiff' file.