This document discusses Java collections and provides examples of ArrayList and HashMap. It introduces collections as objects that group multiple elements and describes the two main collection hierarchies - Collection and Map. It then gives code examples demonstrating common operations on ArrayList like add, remove, contains and clear. Examples are also provided for HashMap operations including put, get, containsKey and remove.

1. Chapitre 3
Les collections
Mouna Torjmen Khemakhem

2. Introduction
• Collection :
objet qui regroupe de multiples éléments dans une seule entité.
• Utilisation de collections pour
- stocker, retrouver et manipuler des données
- transmettre des données d ’une méthode à une autre
• Par exemple, un tableau est une collection
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• Par exemple, un tableau est une collection
• Le JDK fournit d’autres types de collections sous la forme de classes et
d’interfaces
• Ces classes et interfaces sont dans le paquetage java.util
•Avant le JDK 5.0, les collections peuvent contenir des objets de n’importe quel
type
• A partir du JDK 5.0, on peut indiquer le type des objets contenus dans une
collection grâce à la généricitéMouna Torjmen Khemakhem

3. Types de collections
2 hiérarchies principales :
- Collection<E>
- Map<K,V>
• Map correspond aux collections indexées par des clés:
un élément de type V d’une map est retrouvé
rapidement si on connaît sa clé de type Krapidement si on connaît sa clé de type K
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Mouna Torjmen Khemakhem
• Une classe exemple de Collection: ArrayList
import java.util.ArrayList;
• Une classe exemple de Map: HashMap
import java.util.HashMap;

4. ArrayList
import java.util.ArrayList;
import java.util.Arrays;
public class ArrayListTest {
public static void main(String args[])
ArrayList<String> list = new ArrayList<String>();
//add
list.add("Apple");
list.add("Google");
list.add("Samsung");
list.add("Microsoft");
//checking if ArrayList is empty
System.out.println(« Empty ? " +
list.isEmpty());
// removing an Object from ArrayList
System.out.println(« Before removing : " +
list);
list.remove(3); //removing fourth object
System.out.println("after removing : " + list);
// finding index of Object in List
System.out.println("What is index of Apple: "list.add("Microsoft");
//contains: use of equals method
System.out.println("Does list contains Apple :" +
list.contains("Apple"));
System.out.println("Does list contains Verizon :" +
list.contains("Verizon"));
// size
System.out.println("Size of ArrayList is : " +
list.size());
// replacing an object
System.out.println("before updating : " + list);
list.set(3, "Bank of America");
System.out.println("after update : " + list);
}
System.out.println("What is index of Apple: "
+ list.indexOf("Apple"));
// converting List to Array
String[] array = list.toArray(new String[]{});
System.out.println("Array from ArrayList : " +
Arrays.toString(array));
// removing all elements
list.clear();
System.out.println("Size of ArrayList after
clear : " + list.size());
}
4
Mouna Torjmen Khemakhem

5. Output ArrayList
/*
Does list contains Apple :true
Does list contains Verizon :false
Size of ArrayList is : 4
list before updating : [Apple, Google, Samsung, Microsoft]
list after update : [Apple, Google, Samsung, Bank of America]list after update : [Apple, Google, Samsung, Bank of America]
Does this ArrayList is empty : false
ArrayList before removing element : [Apple, Google, Samsung, Bank of
America]
ArrayList after removing element : [Apple, Google, Samsung]
What is index of Apple in this list : 0
Array from ArrayList : [Apple, Google, Samsung]
Size of ArrayList after clear : 0
*/
http://java67.blogspot.com/2012/11/java-arraylist-example-contains-add-set.htmlMouna Torjmen Khemakhem

6. HashMap
import java.util.HashMap;
import java.util.Iterator;
public class HashMapExample{
public static void main(String args[]){
HashMap hashMap = new HashMap();
// adding value into HashMap
hashMap.put("One", new Integer(1));
hashMap.put("Two", new Integer(2));
hashMap.put("Three", new Integer(3));
System.out.println("HashMap size" + hashMap.size() );
Integer one = (Integer) hashMap.get("One");
System.out.println("Value mapped with key
"One" is " + one);
System.out.println("Retrieving all keys ");
Iterator iterator = hashMap.keySet().iterator();
while(iterator. hasNext()){
System.out.println(iterator.next());
}
if(hashMap.containsValue(new Integer(1))){
System.out.println("HashMap contains 1 as value");
}else{
System.out.println("HashMap does not contain 1 as
value");
}
if( hashMap.containsKey("One") ){
System.out.println("HashMap contains One as key");
}else{
System.out.println("HashMap does not contain One
as value");
}
}
System.out.println("Retrieving all values ");
iterator = hashMap.entrySet().iterator();
while(iterator. hasNext()){
System.out.println(iterator.next());
}
System.out.println( hashMap.remove("One") + "
is removed from the HashMap.");
}
}
6
Mouna Torjmen Khemakhem

7. Output HashMap
/*
OUTPUT of the above given Java HashMap Example would be :
HashMap contains 3 key value pair.
HashMap contains 1 as value
HashMap contains One as key
Value mapped with key "One" is 1
Retrieving all keys from the HashMapRetrieving all keys from the HashMap
Three
Two
One
Retrieving all values from the HashMap
Three=3
Two=2
One=1
1 is removed from the HashMap.
*/
http://www.javadeveloper.co.in/java-example/java-hashmap-example.htmlMouna Torjmen Khemakhem