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Inner classes do not have to be anonymous as shown in the above examples. They can be named as well.

Access specifier

Just like any other class, a class defined inside of another class can be public , protected , package private, or private .

Extensibility specifier

Just like a regular class, a final nested/inner class cannot extended.

Abstract specifier

Just like a regular class, an abstract nested/inner class cannot be instantiated.

Inheritance specifier

Just like a regular class, an nested/inner can extend any non-final class and implement any number of interfaces that are within its scope.

Usage

Nested classes are used mostly to avoid name clash and to promote and enforce information hiding. For example the specialized double precision geometric point class, Point2D.Double is defined as an nested class of Point2D which is in turn a nested class of Point . In such, it has access to all the functionality of its parent plus it avoids the name clash with the double precision number class, Double

Inner classes are used to create (at run-time) objects that have direct access to the internals of the outer object and perform complex tasks that simple methods cannot do. Most of the time, they are defined anonymously. For examples, " event listeners " for Java GUI components are implemented as inner classes. The dynamic behavior and versatility of these "listeners" cannot be achieved by the addition of a set of fixed methods to a GUI component. We shall study Java event handling soon!

An inner object can be thought as an extension of the outer object.

6. closure

In functional programming, the closure of a function ( lamdba ) consists of the function itself and an environment in which the function is well-defined. In Java, a function is replaced by a class. An inner class is only defined in the context of its outer object (and the outer object of the outer object, etc...). An inner class together with its nested sequence of outer objects in which the inner class is well-defined is the equivalent of the notion of closure in functional programming. Such a notion is extremely powerful. Just like knowing how to effectively use lambda expressions and higher order functions is key to writing powerful functional programs in Scheme, effective usage of anonymous inner classes is key to writing powerful OO programs in Java.

Some important points to remember about closures and inner classes:

  • An object's closure is defined at the time of its creation.
  • An object "remembers" its closure for its entire lifetime.
  • An inner object's closure includes any local variables that are declared as final , plus all fields of the enclosing object, including private ones.
  • Every time a factory method is run, where a new anonymous object is created, a new closure for that object is created. This is because the local variables could change between calls.
  • Closures enable decoupled communication because an inner class can communicate with its outer class through its closure.

One of the most important ways in which we will use anonymous inner classes it to take advantage of their closure properties. Anonymous inner classes are the only objects in Java that can be instantiated in such a manner that the variables in their environments (closures) can be dynamically defined. That is, since an anonymous inner class can reference a local variable (that is declared final ) and since local variables are created every time a method is called, then every the anonymous inner class object created has a different set of dynamically created variables that it is referencing. This means that we can make unique objects with unique behaviors at run time.

Questions & Answers

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
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
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
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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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