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Generics

The code in this series of modules is written with no thought given to Generics . As a result, if you copy and compile the code, you will probably get warnings 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.

Discussion and sample code

Illustration of core collection interfaces

We will begin this module with a little quiz. Take a look at the program shown in Listing 1 and see if you can answer the following question.

What output does the program in Listing 1 produce?

  • A. Compiler Error
  • B. Runtime Error
  • C. 44321 44321
  • D. 12344 12344
  • E. 1234 44321
  • F. 1234 4321
  • D. None of the above.
Listing 1 . The program named Ap401.
import java.util.TreeSet; import java.util.ArrayList;import java.util.Collection; import java.util.Iterator;public class Ap401{ public static void main(String args[]){ new Worker().doIt();}//end main() }//end class Ap401class Worker{ public void doIt(){Collection ref = new TreeSet(); Populator.fillIt(ref);Iterator iter = ref.iterator(); while(iter.hasNext()){System.out.print(iter.next()); }//end while loopSystem.out.print(" "); ref = new ArrayList();Populator.fillIt(ref); iter = ref.iterator();while(iter.hasNext()){ System.out.print(iter.next());}//end while loop System.out.println();}//end doIt() }// end class Workerclass Populator{ public static void fillIt(Collection ref){ref.add(new Integer(4)); ref.add(new Integer(4));ref.add(new Integer(3)); ref.add(new Integer(2));ref.add(new Integer(1)); }//end fillIt()}//end class populator

If you selected the following answer, then you are correct.

E. 1234 44321

The program in Listing 1 illustrates the basic purpose of the core collection interfaces in the Java Collections Framework. That purposeis to allow collections to be manipulated without regard for how the collections are implemented.

Multiple list implementations

For example, there is more than one way to implement a list. Two common ways involve arrays and linked structures. If two lists are implemented indifferent ways, but both satisfy the requirements of the core collection interfaces, they can each be manipulated the same way regardless of the detailsof their implementation.

TreeSet and ArrayList

A collection of type TreeSet and a collection of type ArrayList are instantiated in the program in Listing 1 . Each of the collections is viewed as being of the interface type Collection . A method named add is used to populate each collection with the same values in the same order.

Behavior is different but appropriate

The behavior of the add method is appropriate, and different in each of the two cases, with the final contents of each collection being determined bythe respective behavior of the add method for that type of collection.

The fillIt method

The code in the fragment shown in Listing 2 defines a static method named fillIt of the class named Populator . This is a class of my own design intended solely to illustrate the primary point of this program.

Questions & Answers

what is mutation
Janga Reply
what is a cell
Sifune Reply
how is urine form
Sifune
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mahase Reply
classification of plants, gymnosperm features.
Linsy Reply
what is the features of gymnosperm
Linsy
how many types of solid did we have
Samuel Reply
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Samuel
What is Atoms
Daprince Reply
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Merolyn
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Merolyn
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Eduek Reply
urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
onuoha Reply
State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
Jeremiah
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Konadu
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Rahma
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Diamond
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Naomi
Malaria is cause by female anopheles mosquito
Isaac
Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
Olalekan
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Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
Muhsin Reply
respiration is the process in which we breath in oxygen and breath out carbon dioxide
Achor
how are lungs work
Commander
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Achiri Reply
in the mouth
EZEKIEL
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Rashima Reply
stimulates the follicle to release the mature ovum into the oviduct
Davonte
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Chinaza
endocrine secrete hormone and regulate body process
Achor
while pituitary gland is an example of endocrine system and it's found in the Brain
Achor
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Egbodo Reply
Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
Alfreda
Biology is the study of how living organisms live and survive in a specific environment
Sifune
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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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