HashMap null issue

Question

What is the difference between the result.

• When I have a null value with a key

• When the key itself does not exist

In the above example, both conditions result are zero. So how can I determine my key value

Map map = new HashMap();
map.put(1,null);
System.out.println(map.get(1));
System.out.println(map.get(2));

Answer:

null

null

Answer 1

While it getreturns the same result for a value nulland a nonexistent key, it containsKeydoes not:

map.containsKey(1)will return true.

map.containsKey(2)will return false.

Also, if you iterate over the keys Map(using keySet()), it 1will be there, 2not it will be.

Answer 2

Hashmap null, Value. , :

if( map.get(1) != null ){
     //
}

Answer 3

Check if the value is null to avoid zero fingerprints.

pseudo code:

//For inputting
if(object != null){
   map.put(1, object);
}
//For getting the value
if(value != null){
     map.get(value)
  }