在存储在HashMap中的ArrayList中搜索值

Question

I am trying to figure out how to retrieve a value that is stored in an ArrayList, stored in a Hashmap.

Here's what I have:

HashMap<String, ArrayList<Record>> records = new HashMap<>();

The key in this hashmap is not what I am looking for. There is a method inside of the Record object called getRecordId() and I want to be able to evaluate whether or not this recordId , through an if statement, exists in the ArrayList.

Example:

if(records.values.exists(recordId)){ ...do something ...}

Essentially, I want to loop through all the values in the ArrayList to see if that record ID exists, and if it does, I will store the key and compute some things. How to I do this?

Edit: right after posting this question, I think I am on to something. How about this:

Set<Map.Entry<String, ArrayList<Record>>> entrySet = records.entrySet();
for(Map.Entry<String, ArrayList<Record>> data : entrySet)
{
    for(Record entry : data.getValue())
    {
        if(recordId.equals(entry.getRecordId()))
        {
            // Do something here
            return "";
        }
    }
}

I need to leave the loops if the record ID has been found, because record IDs are unique.

Answer 1

You can use here Hashmap.entrySet() to get the list of all the keys, and iterate through that key set, and check if recordId exists in the ArrayList for that particular iteration, then store the key and do your computations.

If you are not sure about the syntax and usage of entrySet then you can look into it here - https://www.geeksforgeeks.org/iterate-map-java/

Answer 2

You can use the following syntax :

records.forEach((k, v) -> {
    if (v.contains(recordId)) {
        // do something with 'k'
    }
});

Here we are iterating over the map using forEach . The k stands for the key and the v stands for the value. You can also achieve the same using the entrySet

records.entrySet().forEach(e -> {
    if (e.getValue().contains(recordId)) {
        // do something with 'e.getKey()'
    }
});

Answer 3

for (Map.Entry<String, ArrayList> data : records) {
            ArrayList list = (ArrayList) data.getValue();
            for (int i = 0; i < list.size(); i++) {
                if (list.get(i).equals(recordId)) {
                    // do something
                }
            }
        }

Answer 4

If you are using Java 8 you can use stream :

//List of keys which contains your desired Record at it's value(ArrayList)
List<String> requiredListOfKeys = records.keySet().stream()
                                                  .filter(x -> records.get(x)
                                                  .contains(record))
                                                  .collect(Collectors.toList());

Answer 5

One way to go would be to stream the map values, and for each value (which is a list), stream it and find the first Record instance that matches your search criteria. Then, if such record was found, do whatever you want to do with it:

boolean found = records.values().stream()
    .flatMap(List::stream) // or .flatMap(list -> list.stream())
    .filter(entry -> recordId.equals(entry.getRecordId()))
    .findFirst()
    .ifPresent(entry -> {
        // do something with the found record
    });