Java Collection - 如何创建不应允许更新或删除元素的最终HashMap

import java.util.Collections;
import java.util.Hashtable;
import java.util.Map;

public class Main {
  public static void main(String[] s) {
    Hashtable<String, String> table = new Hashtable<String, String>();

    table.put("1", "Sunday");
    table.put("2", "Monday");
    table.put("3", "Tuesday");
    table.put("4", "Wednesday");
    table.put("5", "Thursday");
    table.put("6", "Friday");
    table.put("7", "Saturday");

    System.out.println("Initial collection: " + table);

    Map m = Collections.unmodifiableMap(table);

    // m.put("key3", "value3");
  }
}