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Such a conversion will often result in the loss of data, and that loss is the responsibility of the programmerwho performs the cast.

Assignment compatibility for references

Assignment compatibility for references doesn't involve range issues, as is the case with primitives. Rather, the reference to an object instantiated from agiven class can be assigned to (is assignment-compatible with):

  1. Any reference variable whose type is the same as the class from which the object was instantiated.
  2. Any reference variable whose type is a superclass of the class from which the object was instantiated.
  3. Any reference variable whose type is an interface that is implemented by the class from which the object was instantiated.
  4. Any reference variable whose type is an interface that is implemented by a superclass of the class from which the object was instantiated.
  5. A couple of other cases involving interfaces that extend other interfaces.

In this module, we are interested only in cases 1 and 2 above. We will be interested in the other cases in future modules involving interfaces.

Such an assignment does not require the use of a cast operator.

Type Object is completely generic

As mentioned earlier, a reference to any object can be assigned to a reference variable of the type Object , because the Object class is a superclass of every other class.

Converting reference types with a cast

Assignments of references, other than those listed above, require the use of a cast operator to purposely change the type of the reference.

However, it is not possible to perform a successful cast to convert the type of a reference to another type in all cases.

Generally, a cast can only be performed among reference types that fall on the same ancestral line of the class hierarchy, or on an ancestral line of aninterface hierarchy. For example, a reference cannot be successfully cast to the type of a sibling or a cousin in the class hierarchy.

Downcasting

When we cast a reference along the class hierarchy in a direction away from the root class Object toward the leaves , we often refer to it as a downcast .

While it is also possible to cast in the direction from the leaves to the root , this conversion happens automatically, and the use of a cast operator is not required.

Preview

A sample program is provided that illustrates much of the detail involved in type conversion, method invocation, and casting with respect to referencetypes.

Discussion and sample code

The program named Polymorph02 , shown in Listing 11 near the end of the module illustrates the use of the cast operator with references.

When you examine that program, you will see that two classes named A and C each extend the class named Object . Hence, we might say that they are siblings in the class hierarchy.

Another class named B extends the class named A . Thus, we might say that A is a child of Object , and B is a child of A .

The class named A

The definition of the class named A is shown in Listing 1 . This class implicitly extends the class named Object by default.

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, Xna game studio. OpenStax CNX. Feb 28, 2014 Download for free at https://legacy.cnx.org/content/col11634/1.6
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