How to iterate through LinkedHashMap with lists as values

Question

I have following LinkedHashMap declaration   LinkedHashMap lt String  ArrayList lt String gt  gt  test1   my point is how can i iterate through this hash map  I want to do this following  for each key get the corresponding arraylist and print the values of the arraylist one by one against the key   I tried this but get only returns string   String key   iterator next   toString      ArrayList lt String gt  value    ArrayList lt String gt   test1 get key

User · Accepted Answer

for  Map Entry lt String  ArrayList lt String gt  gt  entry   test1 entrySet          String key   entry getKey        ArrayList lt String gt  value   entry getValue           now work with key and value        By the way  you should really declare your variables as the interface type instead  such as Map lt String  List lt String gt  gt

User · Answer

I m assuming you have a typo in your get statement and that it should be test1 get key    If so  I m not sure why it is not returning an ArrayList unless you are not putting in the correct type in the map in the first place   This should work      populate the map Map lt String  List lt String gt  gt  test1   new LinkedHashMap lt String  List lt String gt  gt     test1 put  key1   new ArrayList lt String gt      test1 put  key2   new ArrayList lt String gt          loop over the set using an entry set for  Map Entry lt String List lt String gt  gt  entry   test1 entrySet       String key   entry getKey      List lt String gt value   entry getValue                 or you can use      second alternative - loop over the keys and get the value per key for  String key   test1 keySet        List lt String gt value   test1 get key                You should use the interface names when declaring your vars  and in your generic params  unless you have a very specific reason why you are defining using the implementation

User · Answer

iterate over the map for Entry lt String  ArrayList lt String gt  gt  entry   test1 entrySet            iterate over each entry     for String item   entry getValue                print the map s key with each value in the ArrayList         System out println entry getKey            item

User · Answer

You can use the entry set and iterate over the entries which allows you to access both  key and value  directly   for  Entry lt String  ArrayList lt String gt  gt  entry   test1 entrySet          System out println entry getKey           entry getValue            I tried this but get only returns string   Why do you think so  The method get returns the type E for which the generic type parameter was chosen  in your case ArrayList lt String gt

User · Answer

In Java 8   Map lt String  List lt String gt  gt  test1   new LinkedHashMap lt String  List lt String gt  gt     test1 forEach  key value  - gt        System out println key     - gt      value

[java] How to iterate through LinkedHashMap with lists as values

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