java如何从地图的元素创建对象

Question

所以我现在有：

  public static JavaFact register(JavaFact jf){
    Scanner input = new Scanner(System.in);
    Map<String, Activity> activities = new HashMap<String, Activity>();
    Map<String, Activity> companyActivities = new HashMap<String, Activity>();

    activities = jf.getAllActivities //this is just to get all the existent 
   // activities into the Map activities

    System.out.println("How many activities is the user envolved in?");
    int count = input.nextInt();
    for(int i = 0; i<count; i++){
         System.out.println("Insert activity code");
         String code = input.nextLine();
         Activity a = activities.get(code);
         companyAcitivities.put(code, a.clone()); //the error refers to this line
    }
}

在main上运行之后，我得到了一个NullPointerException。我该怎么解决这个问题？我想让用户插入Activity的代码，然后将Activity添加到companyActivities中，其中将包含与所讨论的Company对应的所有活动的Map

Answer 1

要避免出现NullPointerException，请按照其他人在上面的评论中的建议，尝试以下方法：

for(int i = 0; i<count; i++){
     System.out.println("Insert activity code");
     String code = input.nextLine();
     Activity a = activities.get(code);

     if(a != null) {
         companyAcitivities.put(code, a.clone()); //the error refers to this line
     }
}