CODEWITHSUNDEEP
javacollectionsjava-8hashmapjava-stream
Lucifer Morningstar
Lucifer Morningstar

Reputation: 139

Non-static method cannot be referenced from a static context when flattening map java 8

I have a Map<Integer, Map<String, List< String >>. I want to flatten it to Map<String, String> where the key is the inner map's key and the value is the inner map's lists first element using java 8.

Here is what I have so far

public static void main(String[] args) {
    Map<Integer, Map<String, List<String>>> ip = new HashMap<>();
    Map<String, List<String>> iip1 = new HashMap<>();
    List<String> ilp1 = new ArrayList<>();
    ilp1.add("Uno");
    ilp1.add("Dos");
    ilp1.add("Tres");
    iip1.put("Alpha", ilp1);

    Map<String, List<String>> iip2 = new HashMap<>();
    List<String> ilp2 = new ArrayList<>();
    ilp2.add("One");
    ilp2.add("Two");
    ilp2.add("Three");
    iip2.put("Beta", ilp2);

    Map<String, List<String>> iip3 = new HashMap<>();
    List<String> ilp3 = new ArrayList<>();
    ilp3.add("Eins");
    ilp3.add("Zwei");
    ilp3.add("Drei");
    iip3.put("Gamma", ilp3);

    ip.put(1, iip1);
    ip.put(2, iip2);
    ip.put(3, iip3);
    
    
    Map<String, String> op = 
       ip.values().stream().collect(Collectors.toMap(Map.Entry::getKey, e -> 
       e.values().stream().map(ele -> ele.get(0))));
    System.out.println(op);
}

However, I get an error for Map.Entry::getKey saying Non-static method cannot be referenced from a static context.

Not sure what is the issue here, Any help is much appreciated.

Upvotes: 1

Views: 555

Answers (1)

Youcef LAIDANI
Youcef LAIDANI

Reputation: 60045

You have to use flatMap first to get all the entrySet, and then you can use Collectors.toMap, like this:

Map<String, String> op = ip.values().stream()
        .flatMap(e -> e.entrySet().stream())
        .collect(Collectors.toMap(Map.Entry::getKey, e -> e.getValue().get(0)));

Upvotes: 5

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