Java 集合 检查HashMap是否为空

用于检查HashMap是否为空的程序。我们使用HashMap类的isEmpty()方法来执行此检查。

程序

import java.util.HashMap;
class HashMapIsEmptyExample{

  public static void main(String args[]) {

    // Create a HashMap
    HashMap<Integer, String> hmap = new HashMap<Integer, String>(); 

    // Checking whether HashMap is empty or not
    /* isEmpty() method signature and description -
     * public boolean isEmpty(): Returns true if this map 
     * contains no key-value mappings.
     */
    System.out.println("Is HashMap Empty? "+hmap.isEmpty());

    // Adding few elements
    hmap.put(11, "Jack");
    hmap.put(22, "Rock");
    hmap.put(33, "Rick");
    hmap.put(44, "Smith");
    hmap.put(55, "Will");

    // Checking again
    System.out.println("Is HashMap Empty? "+hmap.isEmpty());
  } 
}

输出：

Is HashMap Empty? true
Is HashMap Empty? false