Transcript Lecture 10

Software Construction
Lecture 10
Frameworks
Agenda & Reading
Topics:
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Frameworks
Extensibility
Inversion of Control
Java Frameworks
Advantages & Disadvantages
Reading
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Software framework Wikipedia
Frameworks in Java
Framework
Generic software platform for a certain type of
applications
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Consists of parts that are found in many apps of that type
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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:
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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
Framework Examples
Web Application Frameworks
GUI
Toolkits
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Extensibility
All frameworks can be extended to cater for app-specific
functionality.
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A framework is intended to be extended to meet the needs of
a particular application
Common ways to extend a framework:
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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:
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Subclassing & overriding methods
Implementing interfaces
Registering event handlers
Inversion of Control
A framework employs an inverted flow of control
between itself and its clients.
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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.
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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
Inversion of Control
Traditional Program Execution
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The app has control over the
execution flow, calling library
code when it needs to.
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Inversion of Control
The framework has control over
the execution flow, calling app
code for app-specific behavior.
Inversion of Control
Example: Java Applets
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What is Java Frameworks?
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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
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It is a unified architecture for representing and manipulating collections
It contains Interfaces, Implementations and algorithms
Collections Framework
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The Java Collections Framework provides the following
benefits:
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Reduces programming effort
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Increases program speed and quality
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It provides high-performance, high-quality implementations of useful
data structures and algorithms
Fosters software reuse
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Concentrate on the important parts of your program rather than on
the low-level "plumbing" required to make it work.
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.
Frameworks VS libraries
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Framework uses your code because it is usually the
framework that is in control.
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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.
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Advantages
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Reuse can save cost and time
Higher level of abstraction
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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)
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Disadvantages
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Can lead to code bloat
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Cost of learning a framework
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Framework may contain lots of unused code
May need to use several frameworks
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.
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GUI Programming Concepts
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conventional programming:
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sequence of operations is determined
by the program
what you want to happen, happens when you want it
event-driven programming:
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sequence of operations is determined
by the user’s interaction with the application’s interface
anything that can happen, happens at any time
GUI Design Concepts
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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
GUI Programming Concepts in Java
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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
Java GUI history: the AWT
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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
Swing in Java
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Swing(Java 2, JDK 1.2+)
lightweight components that do not rely on the
native GUI or OS
“look and feel” of Swing components
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are identical on different platforms
can be customized
Swing inherits from AWT
AWT still used for events, layouts
Swing Components in Java
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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.