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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

how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
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what is nano technology
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what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele 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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