hashmap cannot be cast to list

The error "hashmap cannot be cast to list" occurs when you try to assign or convert a HashMap object to a List object directly, but they are incompatible types.

HashMap is a key-value pair data structure that implements the Map interface, while List is an ordered collection of elements that allows duplicates and implements the List interface.

To resolve this issue, you need to convert the HashMap into a List by extracting the values or keys from the HashMap and adding them to the List. Here's an example:

import java.util.*;

public class Example {
    public static void main(String[] args) {
        HashMap<Integer, String> hashMap = new HashMap<>();
        hashMap.put(1, "One");
        hashMap.put(2, "Two");
        hashMap.put(3, "Three");

        List<String> list = new ArrayList<>(hashMap.values());        // OR
        // List<Integer> list = new ArrayList<>(hashMap.keySet());

        System.out.println(list);
    }
}

In this example, we extract the values from the HashMap using the `values()` method and create a new ArrayList with those values. Alternatively, you can use `keySet()` method to extract the keys and add them to the List.

Make sure to choose the appropriate data type for your List based on the values or keys you want to extract from the HashMap.