1. Software Construction Lecture 10 Frameworks

2. Agenda & Reading Topics: Reading Frameworks Extensibility
Inversion of Control
Java Frameworks
Advantages & Disadvantages
Reading
Software framework Wikipedia
Frameworks in Java

3. Framework Generic software platform for a certain type of applications
Consists of parts that are found in many apps of that type
Libraries with APIs (classes with methods etc.)
Ready-made extensible programs ("engines")
Sometimes also tools (e.g. for development, configuration, content)
Often evolved by developing many apps of that type and reusing code more and more
Characteristics:
Reusable: the parts can be used for many apps of that type
Extensible: developers can add their own app-specific code
Inversion of Control: framework often calls your code

4. Web Application Frameworks
Framework Examples
Web Application Frameworks
GUI Toolkits

5. Extensibility
All frameworks can be extended to cater for app-specific functionality.
A framework is intended to be extended to meet the needs of a particular application
Common ways to extend a framework:
Extension is carried out by sub-classing, overriding methods, and implementing interfaces
Plug-ins: framework can load certain extra code in a specific format
Within the framework language:
Subclassing & overriding methods
Implementing interfaces
Registering event handlers

6. Inversion of Control
A framework employs an inverted flow of control between itself and its clients.
When using a framework, one usually just implements a few callback functions or specializes a few classes, and then invokes a single method or procedure.
The framework does the rest of the work for you, invoking any necessary client callbacks or methods at the appropriate time and place.
i.e. "Don't call us, we'll call you.“, or "Leave the driving to us.“
Example: Java's Swing and AWT classes.
They have a huge amount of code to manage the user interface, and there is inversion of control because you start the GUI framework and then wait for it to call your listeners

7. Inversion of Control Traditional Program Execution
The app has control over the execution flow, calling library code when it needs to.
The framework has control over the execution flow, calling app code for app-specific behavior.

8. Inversion of Control Example: Java Applets

9. What is Java Frameworks?
Frameworks are large bodies (usually many classes) of prewritten code to which you add your own code to solve a problem in a specific domain.
In Java technology there are so many frameworks that helps the programmers to build complex applications easily. Examples:
GUI Framework: eg Java's Swing and AWT classes
Collection Framework/library
It is a unified architecture for representing and manipulating collections
It contains Interfaces, Implementations and algorithms

10. Collections Framework
The Java Collections Framework provides the following benefits:
Reduces programming effort
Concentrate on the important parts of your program rather than on the low-level "plumbing" required to make it work.
Increases program speed and quality
It provides high-performance, high-quality implementations of useful data structures and algorithms
Fosters software reuse
New data structures that conform to the standard collection interfaces are by nature reusable. The same goes for new algorithms that operate on objects that implement these interfaces.

11. Frameworks VS libraries
Framework uses your code because it is usually the framework that is in control.
It means the framework controls the sequence and logic of some operation and calls your code to provide certain details
You make use of a framework by calling its methods, inheritance, and supplying "callbacks", listeners, etc
Note: although sometimes large libraries are referred to as frameworks, this is probably not the most common use of the term.

12. Advantages Reuse can save cost and time Higher level of abstraction
Frameworks provides a standard working system through which user can develop the desired module of application or complete application instead of developing lower level details.
Developers can devote more time in developing the software requirement
Reduced maintenance cost (if the framework is maintained by someone else)

13. Disadvantages Can lead to code bloat Cost of learning a framework
Framework may contain lots of unused code
May need to use several frameworks
Cost of learning a framework
Spend more time in assessing the concept, function and its uses in developing the program.
Licensing cost (for commercial frameworks)
A generic ‘one-size-fits-all’ does not work so efficiently for any specific software. There is need to extend framework with specific code to develop any specific software.

14. GUI Programming Concepts
conventional programming:
sequence of operations is determined by the program
what you want to happen, happens when you want it
event-driven programming:
sequence of operations is determined by the user’s interaction with the application’s interface
anything that can happen, happens at any time

15. GUI Design Concepts
a wealth of information creates a poverty of attention - Herbert Simon
Principles of good GUI Design
IBM's Design concepts
Saul Greenberg's HCI pages
Tim's HCI notes

16. GUI Programming Concepts in Java
Java GUI has components
Windows GUI has controls
Unix GUI has widgets
examples: labels, buttons, check boxes, radio buttons, text input boxes, pull down lists
Swing components: JLabel, JButton, JCheckBox, JRadioButton, JTextField, JTextArea, JComboBox

17. Java GUI history: the AWT
AWT(JDK 1.0, 1.1): Abstract Window Toolkit
package: java.awt, java.awt.event
heavyweight components using native GUI system elements
used for applets until most browsers supported JRE 1.2

18. lightweight components that do not rely on the native GUI or OS
Swing in Java
Swing(Java 2, JDK 1.2+)
lightweight components that do not rely on the native GUI or OS
“look and feel” of Swing components
are identical on different platforms
can be customized
Swing inherits from AWT
AWT still used for events, layouts

19. Swing Components in Java
advanced GUI support. e.g. drag-and-drop
package names: javax.swing, javax.swing.event
components inherit from JComponent
components are added to a top-level container: JFrame, JDialog, or JApplet.