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In other cases, multiple methods have the same name, same return type, and same formal argument list (overridden methods) .

Three distinct forms of polymorphism

From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java:

  • Method overloading
  • Method overriding through inheritance
  • Method overriding through the Java interface

I covered method overloading as one form of polymorphism in a previous module.

We need to backtrack

In this module, I will backtrack a bit and discuss the conversion of references from one type to another.

I will begin the discussion of polymorphism through method overriding and inheritance in the next module. I will cover interfaces in a future module.

Assignment compatibility and type conversion

As a background for polymorphism, you need to understand something about assignment compatibility and type conversion .

A value of a given type is assignment compatible with another type if

  • a value of the first type
  • can be successfully assigned to a variable of the second type.

Type conversion and the cast operator

In some cases, type conversion happens automatically. In other cases, type conversion must be forced through the use of a cast operator .

A cast operator is a unary operator, which has a single right operand. The physical representation of the cast operator is the name of a type inside a pair of matching parentheses, as in:

(int)

Applying a cast operator

Applying a cast operator to the name of a variable doesn't actually change the type of the variable. However, it does cause the contents of the variable to be treated as a different type for the evaluation of the expression in which the cast operator is contained. Thus, the application of a cast operator is a short-term operation.

Primitive values and type conversion

Assignment compatibility issues come into play for both primitive types and reference types.

Values of type boolean can only be assigned to variables of type boolean (you cannot change the type of a boolean ) .

Otherwise, a primitive value can be assigned to any variable of a type

  • whose range is as wide or wider
  • than the range of the type of the value.

In that case, the type of the value is automatically converted to the type of the variable.

(For example, types byte and short can be assigned to a variable of type int without the requirement for a cast because type int has a wider range than either type byte or type short .)

Conversion to narrower range

On the other hand, a primitive value of a given type cannot be assigned to a variable of a type with a narrower range than the type of the value, unless the cast operator is used to force a type conversion.

Oftentimes, such a conversion will result in the loss of data, and that loss is the responsibility of the programmer who performs the cast.

Assignment compatibility for references

Assignment compatibility, with respect to references, doesn't involve range issues, as is the case with primitives. Instead, the reference to an object instantiated from a given class can be assigned to:

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, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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