software construction lecture 10 frameworks. agenda & reading 2 topics: frameworks ...
TRANSCRIPT
Agenda & Reading
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Topics: Frameworks Extensibility Inversion of Control Java Frameworks Advantages & Disadvantages
Reading Software framework Wikipedia Frameworks in Java
Framework
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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
Extensibility
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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 loadcertain extra code in a specific format
Within the framework language: Subclassing & overriding methods Implementing interfaces Registering event handlers
Inversion of Control
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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
Inversion of Control
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Traditional Program Execution Inversion of Control
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.
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
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: 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.
Frameworks VS libraries
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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.
Advantages
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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)
Disadvantages
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Can lead to code bloat 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.
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
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
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
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
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