Find Keys from Both LinkedHashMap and Store in a List Alternately

Let us first create a LinkedHashMap with key-value pair −

Map<String, String>map1 = new LinkedHashMap<String, String>();
map1.put("1", "Jim");
map1.put("2", "David");
map1.put("3", "Tom");
map1.put("4", "Sam");
map1.put("5", "Steve");

Let us now create another LinkedHashMap with key-value pair −

Map<String, String>map2 = new LinkedHashMap<String, String>();
map2.put("6", "Katie");
map2.put("7", "John");
map2.put("8", "Kane");
map2.put("9", "Chris");

Now, create a new List and store the keys in it for both the above Map −

List<String>list = new ArrayList<String>();
list.addAll(map1.keySet());
list.addAll(map2.keySet());

Example

 Live Demo

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
public class Demo {
   public static void main(String[] args) {
      Map<String, String>map1 = new LinkedHashMap<String, String>();
      map1.put("1", "Jim");
      map1.put("2", "David");
      map1.put("3", "Tom");
      map1.put("4", "Sam");
      map1.put("5", "Steve");
      Map<String, String>map2 = new LinkedHashMap<String, String>();
      map2.put("6", "Katie");
      map2.put("7", "John");
      map2.put("8", "Kane");
      map2.put("9", "Chris");
      List<String>list = new ArrayList<String>();
      list.addAll(map1.keySet());
      list.addAll(map2.keySet());
      System.out.println("Keys...");
      for (String str: list) {
         System.out.println(str);
      }
   }
}

Output

Keys...
1
2
3
4
5
6
7
8
9