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I will teach you the meaning of the consistent with equals requirement and show you how to satisfy that requirement for a new class definition.

Finally, I will show you how to define a new class whose objects are eligible for inclusion in a TreeSet collection.

Discussion and sample code

Generics

The code in this module is written with no thought given to Generics . As a result, if you copy and compile this code, you will probably get a warning about unchecked or unsafe operations .

While you will ultimately need to understand how to use Generics, that is a very complex topic. An understanding of Generics is beyond the scope of thiscourse. Therefore, for purposes of this course, you can simply ignore those warnings.

Begin with a quiz

Let's begin with a quiz to test your prior knowledge of the Collections Framework.

What output is produced by the program shown in Listing 1 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. 44321
  • D. 4321
  • E. 1234
  • F. 12344
  • G. None of the above.
Listing 1 . The program named Comparable04.
//File Comparable04.java import java.util.*;public class Comparable04{ public static void main(String args[]){ new Worker().doIt();}//end main() }//end class Comparable04class Worker{ public void doIt(){Iterator iter; Collection ref;ref = new TreeSet(); Populator.fillIt(ref);iter = ref.iterator(); while(iter.hasNext()){System.out.print(iter.next()); }//end while loopSystem.out.println(); }//end doIt()}// end class Worker class Populator{public static void fillIt(Collection ref){ ref.add(new MyClass(4));ref.add(new MyClass(4)); ref.add(new MyClass(3));ref.add(new MyClass(2)); ref.add(new MyClass(1));}//end fillIt() }//end class Populatorclass MyClass{ int data;MyClass(){ data = 0;}//end noarg constructor MyClass(int data){this.data = data; }//end parameterized constructorpublic String toString(){ return "" + data;}//end overridden toString() }//end MyClass

If your answer was B. Runtime Error , you were correct.

What caused the runtime error?

The runtime error was caused by the code shown in Listing 2 .

Listing 2 . The code with the problem.
class Populator{ public static void fillIt(Collection ref){ref.add(new MyClass(4));

Why did this code produce a runtime error?

This code produced a runtime error for the following reasons.

The incoming parameter of the fillIt method is a reference to an object of type TreeSet but it is received as type Collection . The TreeSet class implements the Collection , Set , and SortedSet interfaces. (In this module, we will be primarily interested in the Set and SortedSet interfaces.)

The contract for the add method of the Set interface reads partially as follows:

"Adds the specified element to this set if it is not already present ... If this set already contains the specified element, the call leaves this setunchanged and returns false. ... this ensures that sets never contain duplicate elements."

What does this mean?

This means that whenever the add method is called on a Set object, the add method must have a way of determining if the element being added is a duplicate of an element that already exists in the collection.This means that it must be possible for the add method to compare the new element with all of the existing elements to determine if the newelement is a duplicate of any of the existing elements.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
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.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit 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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