Answers for "map interface in java"

create map java

Map<String, Integer> map = new HashMap<>();

map java

import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;


public class Main {
   public static void main(String[] args) {

      //La fameuse syntaxe en diamant de Java 7
      Map<Integer, String> hm = new HashMap<>();
      hm.put(10, "1");
      hm.put(20, "2");
      hm.put(30, "3");
      hm.put(40, "4");
      hm.put(50, "5");
      //Ceci va écraser la valeur 5
      hm.put(50, "6");
      
      System.out.println("Parcours de l'objet HashMap : ");
      Set<Entry<Integer, String>> setHm = hm.entrySet();
      Iterator<Entry<Integer, String>> it = setHm.iterator();
      while(it.hasNext()){
         Entry<Integer, String> e = it.next();
         System.out.println(e.getKey() + " : " + e.getValue());
      }
      
      System.out.println("Valeur pour la clé 8 : " + hm.get(8));
      
      Map<Integer, String> lhm = new LinkedHashMap<>();
      lhm.put(10, "1");
      lhm.put(20, "2");
      lhm.put(30, "3");
      lhm.put(40, "4");
      lhm.put(50, "5");
      
      System.out.println("Parcours de l'objet LinkedHashMap : ");      
      Set<Entry<Integer, String>> setLhm = lhm.entrySet();
      Iterator<Entry<Integer, String>> it2 = setLhm.iterator();
      while(it2.hasNext()){
         Entry<Integer, String> e = it2.next();
         System.out.println(e.getKey() + " : " + e.getValue());
      }
   }
}

map in java

MAP : is a (key-value format) 
      and keys are always unique, 
      and value can be duplicated. 
- HashTable don't have null key, sychronized(thread-safe)
- LinkedHashMap can have null key, keeps order
- HasHMap can have null key, order is not guaranteed
- TreeMap doesn't have null key and keys are sorted

Java The Map Interface

//The Map interface maps unique keys to values. A key is an object that you use to retrieve a value at a later date.

Given a key and a value, you can store the value in a Map object. After the value is stored, you can retrieve it by using its key.
Several methods throw a NoSuchElementException when no items exist in the invoking map.
A ClassCastException is thrown when an object is incompatible with the elements in a map.
A NullPointerException is thrown if an attempt is made to use a null object and null is not allowed in the map.
An UnsupportedOperationException is thrown when an attempt is made to change an unmodifiable map.
Example of List, Set, Map
import java.util.*; // All the classes and interfaces are part of the util package
public class CollectionsDemo {

   public static void main(String[] args) {
      // ArrayList 
      List a1 = new ArrayList();
      a1.add("Zara");
      a1.add("Mahnaz");
      a1.add("Ayan");
      System.out.println(" ArrayList Elements");
      System.out.print("\t" + a1);

      // LinkedList
      List l1 = new LinkedList();
      l1.add("Zara");
      l1.add("Mahnaz");
      l1.add("Ayan");
      System.out.println();
      System.out.println(" LinkedList Elements");
      System.out.print("\t" + l1);

      // HashSet
      Set s1 = new HashSet(); 
      s1.add("Zara");
      s1.add("Mahnaz");
      s1.add("Ayan");
      System.out.println();
      System.out.println(" Set Elements");
      System.out.print("\t" + s1);

      // HashMap
      Map m1 = new HashMap(); 
      m1.put("Zara", "8");
      m1.put("Mahnaz", "31");
      m1.put("Ayan", "12");
      m1.put("Daisy", "14");
      System.out.println();
      System.out.println(" Map Elements");
      System.out.print("\t" + m1);
   }
}