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Let us try to override the method equals in classes BParticle and CParticle ; the method returns true if the all fields of the two objects are equal.

  • Four objects are created: two equal objects b1 and b2 of type BParticle and two unequal objects c1 and c2 of type CParticle .
  • As expected, b1.equals(b2) returns true and c1.equals(c2) returns false .
  • b1.equals(c1) returns true : since CParticle is a subclass of BParticle , the variable c1 is acceptable as a parameter to the method equals declared in BParticle . c1 is equal to b1 , because we are only comparing the first two fields inherited from BParticle and these are equal.

Exercise Explain what happens if you try to evaluate c1.equals(b1) .

Program: Inheritance07C.java

// Learning Object Inheritance07C //    equality (robust overriding)class Particle {     int position;      Particle(int p) {        position = p;     }      void newPosition(int delta) {         position = position + delta;    } }  class BParticle extends Particle {    int charge;      BParticle(int p, int c) {         super(p);        charge = c;     }}  class CParticle extends BParticle {     boolean strange;      CParticle(int p, int c, boolean s) {        super(p, c);         strange = s;    }      void newPosition(int delta) {         if (strange)            position = position * charge;     }      public boolean equals(Object obj) {        if (obj == null) return false;         if (!(obj instanceof CParticle)) return false;        CParticle c = (CParticle) obj;         return this.position == c.position && this.charge == c.charge &&               this.strange == c.strange;     }}  class Inheritance07C {     public static void main(/*String[] args*/) {         BParticle b1 = new BParticle(20, 2);        CParticle c1 = new CParticle(20, 2, false);         CParticle c2 = new CParticle(20, 2, true);        CParticle c3 = new CParticle(20, 2, false);         boolean eqc1null = c1.equals(null);        boolean eqc1b1 = c1.equals(b1);         boolean eqc1c2 = c1.equals(c2);        boolean eqc1c3 = c1.equals(c3);     }}

It would be unusual for two objects to be considered equal if they are of different types, even if one type is a subclass of another.In fact, public boolean equals(CParticle c) does not override the method equals in BParticle , because an overriding method must have the same signature as the overridden method.

The method equals is declared in the root class Object as: public boolean equals(Object obj) and this is the method that must be overridden. This program shows the correct technique:

  • Since the parameter can now be any object, a check is first made that the parameter is not null .
  • Similarly, a check is made that the parameter is of the same type as this object.
  • Now that we know that the parameter is actually of this type, it can be cast from Object to the type.
  • Only then is class-specific code performed—usually a field-by-field comparison.

Trace the execution of the program:

  • Four objects are created: one object b1 of type BParticle and three objects c1 , c2 and c3 of type CParticle .
  • Clearly, comparing c1 to null or b1 returns false .
  • Field-by-field comparisons are used if the parameter is of type CParticle : c1.equals(c2) returns false and c1.equals(c3) returns true .

Questions & Answers

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
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
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
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Learning objects for java (with jeliot). OpenStax CNX. Dec 28, 2009 Download for free at http://cnx.org/content/col10915/1.2
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