Map and HashMap difference

Difference

  • Map is an interface but HashMap is a class. So you cannot create an object of a Map but you can create an object of a HashMap
 Map <String, Integer> empIds = new Map<>(); // This will give a compile time error
 Map <String, Integer> empIds = new HashMap<>(); // This is allowed
  • Map contains unique key value pairs but HashMap can have duplicate values.
  • Map interface can be implemented by using its implementing class. Whereas HashMap class implements the Map interface.
  • Map is used to create, Hashmap and TreeMap. While HashMap implements Map interface and extends AbstractMap class.
  • There is no difference between the objects of Map and HashMap. Both of them maintains an insertion order.
  • You are not allowed to use primitive data types (int, float, double, char) to define a Map or a HashMap. You have to use non-primitive data types (Integer, Float, Double, Character, String, Objects) to define a Map or HashMap. 
Example of Map
 public class Maps {
    public static void main(String[] args) {
        Map <String, Integer> empIds = new HashMap<>();
        empIds.put("Shirley", null);
        empIds.put("Raaj", 24372);
        empIds.put("Abhishek", 10082);
        empIds.put("Rahul", 10032);

        System.out.println(empIds);
        System.out.println(empIds.get("Abhishek"));
        System.out.println(empIds.containsKey("Ravi"));
        System.out.println(empIds.containsValue(10032));
        System.out.println(empIds.putIfAbsent("Raaj", 24373));
        System.out.println(empIds.replace("", 24389));
        empIds.remove("Rahul");
        System.out.println(empIds);
    }
 }
Example of HashMap
 public class Maps {
    public static void main(String[] args) {
        HashMap <String, Integer> empIds = new HashMap<>();
        empIds.put("Shirley", null);
        empIds.put("Raaj", 24372);
        empIds.put("Abhishek", 10082);
        empIds.put("Rahul", 10032);

        System.out.println(empIds);
        System.out.println(empIds.get("Abhishek"));
        System.out.println(empIds.containsKey("Ravi"));
        System.out.println(empIds.containsValue(10032));
        System.out.println(empIds.putIfAbsent("Raaj", 24373));
        System.out.println(empIds.replace("", 24389));
        empIds.remove("Rahul");
        System.out.println(empIds);
    }
 }


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