map in java

1Map<String, String> map = new HashMap<>();
2
3for(Entry<String, String> entry:map.entrySet()) {
4  System.out.println("key: "+entry.getKey()+" value: "+entry.getValue());
5}

1
2MAP : is a (key-value format) 
3      and keys are always unique, 
4      and value can be duplicated. 
5- HashTable don't have null key, sychronized(thread-safe)
6- LinkedHashMap can have null key, keeps order
7- HasHMap can have null key, order is not guaranteed
8- TreeMap doesn't have null key and keys are sorted

1import java.util.HashMap;
2import java.util.Iterator;
3import java.util.LinkedHashMap;
4import java.util.Map;
5import java.util.Map.Entry;
6import java.util.Set;
7
8
9public class Main {
10   public static void main(String[] args) {
11
12      //La fameuse syntaxe en diamant de Java 7
13      Map<Integer, String> hm = new HashMap<>();
14      hm.put(10, "1");
15      hm.put(20, "2");
16      hm.put(30, "3");
17      hm.put(40, "4");
18      hm.put(50, "5");
19      //Ceci va écraser la valeur 5
20      hm.put(50, "6");
21      
22      System.out.println("Parcours de l'objet HashMap : ");
23      Set<Entry<Integer, String>> setHm = hm.entrySet();
24      Iterator<Entry<Integer, String>> it = setHm.iterator();
25      while(it.hasNext()){
26         Entry<Integer, String> e = it.next();
27         System.out.println(e.getKey() + " : " + e.getValue());
28      }
29      
30      System.out.println("Valeur pour la clé 8 : " + hm.get(8));
31      
32      Map<Integer, String> lhm = new LinkedHashMap<>();
33      lhm.put(10, "1");
34      lhm.put(20, "2");
35      lhm.put(30, "3");
36      lhm.put(40, "4");
37      lhm.put(50, "5");
38      
39      System.out.println("Parcours de l'objet LinkedHashMap : ");      
40      Set<Entry<Integer, String>> setLhm = lhm.entrySet();
41      Iterator<Entry<Integer, String>> it2 = setLhm.iterator();
42      while(it2.hasNext()){
43         Entry<Integer, String> e = it2.next();
44         System.out.println(e.getKey() + " : " + e.getValue());
45      }
46   }
47}
48

1Map< String,Integer> hm =  
2                        new HashMap< String,Integer>(); 
3       hm.put("a", new Integer(100)); 
4       hm.put("b", new Integer(200)); 
5       hm.put("c", new Integer(300)); 
6       hm.put("d", new Integer(400));