Java Collection - 如何用lambda表达式初始化HashMap

import java.util.HashMap;
import java.util.concurrent.Callable;

public class Main {

  public static void main(String[] args) throws Exception {

    HashMap<Integer, Callable<String>> m = new HashMap<Integer, Callable<String>>() {
      {
        put(0, () -> {
          return "n";
        });
        put(1, () -> {
          return "m";
        });
      }
    };
    System.out.println(m.get(0).call());
  }

}