CS133: Developing Programming Principles

GUI Concepts

Everytime you want a window to appear on screen, use a JFrame.

You can extend JFrame (the way Board does) if you want instance variables or you want to make objects that all appear in their own windows.
You can just create JFrames and add to their content panes otherwise.

If you want to make a custom GUI component (with shapes) then extend JPanel.

The primitive drawing components go into the paintComponent(Graphics canvas) method. The Graphics objects has methods to draw arcs, rectangles, ellipses, etc.
These primitives mostly use the idea of a bounding box.
(0,0) is the top-left pixel of the drawing surface.

In order to get input from the mouse your GUI components must implement Listeners. Each listener reacts to user input in some way.

Each listener is an interface.
Select the methods that are relevant to your application (e.g. mouseClicked) and fill in those method bodies with code that reacts to the event.
Each listening method takes an event of some kind. Each of those events has its own methods (to get text strings, refer to objects, return pixel positions, and so on)
The listener must be implemented by some class (in this course often by the JPanel or widget subclass itself). You then need to add an instance of the listener to the appropriate widget (e.g. addMouseListener for JPanels).

Swing provides a bunch of interactive widgets you can use for building GUIs: JButtons, JTextFields, JLabels, JSliders, ...

You can add these directly to your applications or you can make a subclass that adds instance variables and other methods.
Each of these widgets has associated listeners (e.g. ActionListener)

Layout managers are used to lay out different GUI components in a JPanel. You can nest layout managers inside each other

Relevant managers:

GridLayout: Arranges components row-wise in a grid
FlowLayout: The default. Arranges components left to right with "word wrap". The layout changes as the user grows and shrinks the window.
BorderLayout: Made of five different layouts: NORTH, SOUTH, EAST, WEST, CENTER. You can put JPanels inside each of these. This is good for applications which should be surrounded by buttons.

Often we break down programs with GUIs into "Application Logic" and "User Interface". This allows us to debug each individually.
In the Calculator demo we made an abstract class called CalculatorButton which updated the display and had an abstract pressed method. Subclasses of CalculatorButton implemented operators, digits, and so on.