Java Collection - 如何获取HashMap的大小

import java.util.HashMap;

public class Main {
  public static void main(String[] args) {
    HashMap<String,String> hMap = new HashMap<String,String>();

    System.out.println("Size of HashMap : " + hMap.size());

    hMap.put("1", "One");
    hMap.put("2", "Two");
    hMap.put("3", "Three");

    System.out.println("Size of HashMap after addition : " + hMap.size());

    // remove one element from HashMap
    System.out.println(hMap.remove("2"));
  }
}