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The equals method

The equals method is defined in the Object class, and can be overridden in subclasses of Object . It is the responsibility of the author of the subclass to override the method so as to implement thatauthor's concept of "equal" insofar as objects of the class are concerned.

The overridden equals method

The reason that the equals method returned true in this case was that the author of the String class provided an overridden version of the equals method.

The default equals method

If the author of the class does not override the equals method, and the default version of the equals method inherited from Object is called on an object of the class, then according to Sun:

"for any reference values x and y, this method returns true if and only if x and y refer to the same object (x==y has the value true)"

In other words, the default version of the equals method inherited from the class Object provides the same behavior as the == operator when applied to object references.

Back to Question 2

Answer 1

C. Joe Joe false

Explanation 1

The identity operator

This program illustrates the behavior of the == operator (sometimes referred to as the identity operator) when used to compare references to objects.

Two String objects with identical contents

As shown in the following fragment, this program instantiates two objects of the String class containing identical character strings.

class Worker{ void doIt(){char[] anArray = {'J','o','e'};String Str1 = new String(anArray); String Str2 = new String(anArray);

The fact that the two String objects contain identical character strings is confirmed by:

  • Both objects are instantiated using the same array object of type char as input.
  • When the toString representations of the two objects are displayed later, the display of each object produces Joe on thecomputer screen.

Compare object references using identity (==)

The references to the two String objects are compared using the == operator, and the result of that comparison is displayed. This comparison will produceeither true or false. The code to accomplish this comparison is shown in the following fragment.

System.out.println( Str1 + " " + Str2 + " " +(Str1 == Str2));

The statement in the above fragment produces the following display:

Joe Joe false

How can this be false?

We know that the two objects are of the same type ( String ) and that they contain the same character strings. Why does the == operator return false?

Doesn't compare the objects

The answer lies in the fact that the above statement doesn't really compare the two objects at all. Rather, it compares the values stored in the referencevariables referring to the two objects. That is not the same as comparing the objects.

References are not equal

Even though the objects are of the same type and contain the same character string, they are two different objects, located in different parts of memory.Therefore, the contents of the two reference variables containing references to the two objects are not equal.

The correct answer is false

The == operator returns false as it should. The only way that the == operator could return true is if both reference variables refer to the same object, (which is not the case) .

The bottom line is ...

The == operator cannot be used to compare two objects for equality. However, it can be used to determine if two reference variables refer to the same object.

Back to Question 1

-end-

Questions & Answers

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
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket 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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