<< Chapter < Page Chapter >> Page >
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

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Principles of object-oriented programming. OpenStax CNX. May 10, 2013 Download for free at http://legacy.cnx.org/content/col10213/1.37
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Principles of object-oriented programming' conversation and receive update notifications?