java 8 list to map with occurrences

In Java 8 and later, you can use the Collectors.groupingBy method of the Collectors class to create a Map that maps each element in a List to the number of occurrences of that element in the List.

To create a Map that maps elements in a List to their occurrences, you can use the Collectors.groupingBy method in combination with the Collectors.counting method, which returns a Collector that counts the number of input elements.

Here is an example of how you can use the Collectors.groupingBy and Collectors.counting methods to create a Map that maps elements in a List to their occurrences:

import java.util.List;
import java.util.Arrays;
import java.util.Map;
import java.util.stream.Collectors;

public class MyClass {
    public static void main(String[] args) {
        List<String> words = Arrays.asList("apple", "banana", "cherry", "apple", "banana");

        Map<String, Long> map = words.stream()
            .collect(Collectors.groupingBy(s -> s, Collectors.counting()));

        System.out.println(map); // Outputs {apple=2, banana=2, cherry=1}
    }
}

In this example, the wordsList contains five strings: "apple", "banana", "cherry", "apple", and "banana".

The Collectors.groupingBy method groups the elements of the List by their identity, and the Collectors.counting method counts the number of elements.