How to get specific value from ArrayList in POJO in java

Question

Key : 22 Value: Abey
Key : 22 Value : Dawn
Key : 22 Value : Sherry
Key : 22 Value : Sherry
Key : 22 Value : Sherry

I want to print only Keys with Sherry only,how to do it using Java?

Changing title of question because HashMap doesn't store duplicate Keys

Answer 1

HashMap doesn't accept duplicate keys. Only duplicate values. In your approach you can't be able to store all the records as you are showing. for example:

Map<Integer, String> map = new HashMap<>();
map.put(22, "Abey");
map.put(22, "Dawn");
map.put(22, "Sherry");
map.put(22, "Sherry");
map.put(22, "Sherry");

when you print the output of the HashMap. You only get one output because the same key will replace to latest value.

output:

{22=Sherry}

If you really want to store duplicate keys, Learn more about how to store duplicate keys in HashMap.

Answer 2

You can use the below method from JDK1.8 and above to complete the task.

List<Integer> keys = hashMap.entrySet().stream()
            .filter((entry) -> entry.getValue().equals("Sherry"))
            .map(entry -> entry.getKey())
            .collect(Collectors.toList());

Answer 3

I think you need to loop through the map. There is no specific function to do this

map.forEach((k,val) -> {
  if (val.equals("Sherry") {
    keys.add(k);
  }
});

where map is the HashMap and keys is a list

Answer 4

You can use the following code.

static < K, V > List < K > getAllKeysForValue(Map < K, V > mapOfWords, V value) {
    List < K > listOfKeys = null;
    //Check if Map contains the given value
    if (mapOfWords.containsValue(value)) {
        // Create an Empty List
        listOfKeys = new ArrayList < > ();
        // Iterate over each entry of map using entrySet
        for (Map.Entry < K, V > entry: mapOfWords.entrySet()) {
            // Check if value matches with given value
            if (entry.getValue().equals(value)) {
                // Store the key from entry to the list
                listOfKeys.add(entry.getKey());
            }
        }
    }
    // Return the list of keys whose value matches with given value.
    return listOfKeys;
}

Answer 5

Maybe you can use the reverse map, having Sherry, Dawn and Abey as keys, and 22 as the value of list. You can have something like:

Map<String , Set<String> > reverseMap;

Now you can store the keys like 22 in the set and have the key of this map as the name.