Difference between Java Set, List and Map Collections?

Let us see the main differences between Set,List,Map java collections..

Set (Interface)

• Set is an un-ordered collection which doesn’t allows duplicate (no-duplicate) elements
• We can iterate the values by calling iterator() method

Set s = new HashSet();
Iterator iter = s.iterator();

List (Interface)

• List is an ordered collection which allows duplicate elements
• We can iterate the values by calling iterator() method

List li = new ArrayList();
Iterator iter = li.iterator();

Map (Interface)

• In Map we used to store the data in key and value pairs, we may have duplicate values but no duplicate keys
• In Map we don’t have iterator() method, but we can get the keys by calling the method keySet()

Map m; // insert values Set s = m.keySet(); // Get Map keys into the Set and then iterate this Set object normally // m.keySet() returns Set object with Map keys Iterator iter = s.iterator();

1 2 3 4 5

Map m; // insert values Set s = m.keySet(); // Get Map keys into the Set and then iterate this Set object normally // m.keySet() returns Set object with Map keys Iterator iter = s.iterator();