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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

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
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
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
How can I make nanorobot?
Lily
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
how can I make nanorobot?
Lily
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
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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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