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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


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.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
analytical skills graphene is prepared to kill any type viruses .
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.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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