CODEWITHSUNDEEP
javalambdajava-8
Arefe
Arefe

Reputation: 12471

Explain the lambda expression

I have a method that contains a lambda expression:

public int noOfComplementaryPairs1(int arr[], int k) {

    Map<Integer, Integer> map = new HashMap<Integer, Integer>();

    for (int i = 0; i < arr.length; i++) {
        map.merge(k - arr[i], 1, Integer::sum);
    }

    return Arrays.stream(arr).map(element -> map.getOrDefault(element, 0)).sum();
}

Can someone explain to me what the last 2 lines mean? I am not new to Java, but sometimes I get confused with some expressions like this one.

Upvotes: 2

Views: 98

Answers (1)

Eugene
Eugene

Reputation: 121068

map.merge... : the first param is the key in the map, the second param is the value in the map when this key is not present, the third one is a BiFunction that tells u how to merge two keys, since u cant have two keys with the same value inside a Map..

The last line is pretty simple too: you are streaming the array, mapping each element of that array with: map.getOrDefault(element, 0), which means get the value from the map with key = element or the default of zero if it is not present; then sum them all.

Upvotes: 3

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