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Java GUI programming including basic event handling, adapters, and the command and null-object design patterns.

1. jframe with jbuttons and event handlers (frame2.java)

Source code for Frame2.java and the associated Frame2App.java is at the end of this module, or download the entire archive

Command design pattern

When a user clicks on a button, an ActionEvent object is delivered to the button. In order for the button to perform an application specific task, we must register an ActionEventListener to the button and program this event listener to perform the task we want. The ActionListener class is an example of what is called a " command " from the Command Design Pattern . The code to add an ActionListener to a button looks like:

myButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) {// code to perform a task goes here... }});

The example Frame2 (source code at end of the module) shows how to dynamically change the layout manager for a JFrame by calling its setLayout(...) method resulting in a dynamic re-arrangement of the GUI components in the JFrame .

2. jframe with jbuttons and adapters (frame3.java)

Source code for Frame3.java and the associated IView2World.java , Frame3controller.java and Frame3App.java is at the end of this module, or download the entire archive

Frame3 illustrates how to decouple the view from the rest of the world by having the view communicate to an interface called "adapter". A controller object, Frame3Controller connects the view Frame3 to the world by installing a concrete adapter into the view. The adapter is instantiated as anonymous inner object and has access to all of its outer object. The view does not and should not know anything about the world to which it is connected. This adds flexibility to the design.

Null-object pattern

In much of the current programming practice, the special value null is often used as a flag to represent a gamut of different and often disconnected concepts such as emptiness and falseness. This can result in a lot of confusion and complex control structures in the code. In our view, null should only be used to denote the non-existence of an object. null is not an object and has no "intelligence" (i.e. behavior) for other objects to interact with. Therefore, whenever we work with a union of objects and discover that one or more of these objects may be referencing a null value, we almost always have to write code to distinguish null as a special case. To avoid this problem, we should think of adding a special object, called the null object , to the union with appropriate behavior that will allow us to treat all object references in a consistent and uniform way, devoid of special case consideration. This design pattern is called the null object pattern. We have used the null object pattern in one occasion: the EmptyNode to represent the empty state of a (mutable) list ( LRStruct ).

In Frame3 , the view adapter, _v2wAdapter , is initialized to an (anonymous) IView2World object. It is there to guarantee that _ v2wAdapter is always referencing a concrete IView2World object, and , since setV2WAdapter(...) only allows a non-null assignment, we can always call on _ v2WAdapter to perform any method without checking for null .

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Principles of object-oriented programming. OpenStax CNX. May 10, 2013 Download for free at http://legacy.cnx.org/content/col10213/1.37
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