import java.util.*;

public class TestImmutable {
    public static void main(String[] args) {
        HashMap<Integer, Integer> map = new HashMap<>();
        Map<Integer, Integer> immutableMap = Collections.unmodifiableMap(map);
        try {
            immutableMap.put(0, 0);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}