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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:


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

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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