What does the following Java code demonstrate?

import java.util.HashMap;
import java.util.Map;
public class Main {
    public static void main(String[] args) {
        Map<String, String> capitals = new HashMap<>();
        capitals.put("USA", "Washington D.C.");
        capitals.put("Germany", "Berlin");
        capitals.remove("USA");
        System.out.println(capitals.containsKey("USA"));
    }
}