Collect values from List of objects to Map

Question

I have class:

class Employee {
   private Integer id;
   private String name;
   //getters/setters
}

Also I've an Arraylist with employees:

List<Employee> employees = new Arraylist<>();

How can I extract id as a key and name as a value to HashMap (with streams)?

map.put(employee.getId(), employee.getName())

UPDATED

What if I've a custom Lists as fields?

class Employee {
   private List<Filters> filters;
   private String name;
   //getters/setters
}

class Filter {
   String name;
   String keyword;
   //getters/setters
}

And I want to put name (from Filter) as a value, and keyword as a key to map.

which name though? The one from `Employee` or the one from `Filter`? — Lino, Sep 29 '20 at 12:16
You could use `employees.stream().flatMap(e -> e.getFilters().stream()).collect(Collectors.toMap(Filter::getName, Filter::getKeyword));` — Lino, Sep 29 '20 at 12:20

score 1 · Answer 1 · answered Sep 29 '20 at 12:06

1

You can convert using streams as below:

 public Map<Integer, String> convertListToMap(List<Employee> list) {
    Map<Integer, String> map = list.stream()
      .collect(Collectors.toMap(Employee::getId, Employee:: getName));
    return map;
}

answered Sep 29 '20 at 12:06

Umesh Sanwal

681
4
13

1

You can return the stream result directly, no need to store into useless map variable. – Silviu Burcea Sep 29 '20 at 12:09
Updated my question, any tips? – takotsubo Sep 29 '20 at 12:16

score -2 · Answer 2 · answered Sep 29 '20 at 12:06

-2

Map<String,String> map=Maps.newHashMap();
employees.stream().forEach(->{
  map.put(i.getId,i.getName);
});

answered Sep 29 '20 at 12:06

GuoZG

1

`Collectors.toMap` is more elegant. – Silviu Burcea Sep 29 '20 at 12:07
Doesn't even compile, also why use `Maps.newHashMap()` instead of `new HashMap<>()`? – Lino Sep 29 '20 at 12:15

Collect values from List of objects to Map

2 Answers2