将地图的值放在列表中

Question

I have a hashmap that contains, person Id as key, and person object as value.

Map<String, Person> personMap = new HashMap<String,Person>();

The person object (map's value) contains a person Id instance variable that I'd like to compare with user input. My idea is to create an arraylist from the map's values as mentioned here - How to convert a Map to List in Java? , so I can check if the arraylist.contains(userInput).

However, I need a arraylist of strings that contains Person.getPersonId(),please help me here. Can I do it in one step? If there is a better alternative then, please suggest.

Answer 1

At first, you need to get Person values from personMap .

List<Person> persons =personMap.values();

To get arraylist of strings that contains Person.getPersonId(), you need to do following steps.

List<String> personIds=new ArrayList<>();
for(Person p: persons){ // Iterate over persons List
  if(p.getPersonId()!=null){ //Check the personId from Person
    personIds.add(p.getPersonId());
  }
}

Answer 2

Try this:

List<Person> personList = new ArrayList<>(personMap.values());
List<String> idList = personList.stream().map(Person::getPersonId).collect(Collectors.toList());