Java 8 Convert Map to List using Streams API

6 months ago codedestine 0

Java 8 Convert Map to List :- In this tutorial, we will learn to convert map to list using Stream API.

Java 8 Convert Map to List

Problem Statement :-

Given a map of Integer as a key and String as a Value convert it to the list, containing all the values of Map.

Let’s see the implementation of above problem in java 7 and in java 8.

Java 7 :-  To implement this, iterate through the set of map’s Entry object and add it’s value to newly created List object.

  public static void main(String[] args){
 
    Map<Integer,String> map = new HashMap<Integer,String>();
    map.put(1,"Robert");
    map.put(2,"Martin");
    map.put(3,"Jack");
 
    List<String> list = new ArrayList<String>();
 
    Set<Entry<Integer,String>> set = map.entrySet();
    Iterator<Entry<Integer,String>> iterate = set.iterator();
    while(iterate.hasNext()){
      list.add(iterate.next().getValue());
    }
    for(String s : list){
      System.out.println(s);
    }
  }

Java 8 :- To implement this, we will use stream’s map() method.

  public static void main(String[] args){
 
    Map<Integer,String> map = new HashMap<Integer,String>();
    map.put(1,"Robert");
    map.put(2,"Martin");
    map.put(3,"Jack");
 
    List<String> list = map.entrySet().stream().map( v -> v.getValue()).collect(Collectors.toList());
    list.forEach( v -> System.out.println(v)); 
  }

Result :- 

Robert
Martin
Jack

Reference :-  Stream’s map() JavaDocs 

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