User Interfaces

Xlib

(http://tronche.com/gui/x/xlib/introduction/overview.html)

The X Window System supports one or more screens containing overlapping windows or subwindows. A screen is a physical monitor and hardware, which can be either color, grayscale, or monochrome. There can be multiple screens for each display or workstation. A single X server can provide display services for any number of screens. A set of screens for a single user with one keyboard and one pointer (usually a mouse) is called a display.

Each window and pixmap has its own coordinate system. The coordinate system has the X axis horizontal and the Y axis vertical with the origin [0, 0] at the upper-left corner. Coordinates are integral, in terms of pixels, and coincide with pixel centers. For a window, the origin is inside the border at the inside, upper-left corner.

X does not guarantee to preserve the contents of windows. When part or all of a window is hidden and then brought back onto the screen, its contents may be lost. The server then sends the client program an Expose event to notify it that part or all of the window needs to be repainted. Programs must be prepared to regenerate the contents of windows on demand.

Most of the functions in Xlib just add requests to an output buffer. These requests later execute asynchronously on the X server. Functions that return values of information stored in the server do not return (that is, they block) until an explicit reply is received or an error occurs. You can provide an error handler, which will be called when the error is reported.

Java

We can extend ONLY one item, whereas multiple items can be IMPLEMENTED. I couldn't remember exactly how it's done so I'm putting the signature here: 

public class Spreadsheet
    extends Frame
    implements ActionListener, MouseListener{

....}

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Page updated on: 19-Feb-2002 03:40 PM