Retrieve all values from HashMap keys in an ArrayList Java

Question

Good day  this is kind of confusing me now brain freeze   and seem to be missing something  Have an ArrayList which i populate with a HashMap  now i put in my HashMap and arraylist    Map put DATE  value1    Map put VALUE  value2     arraylist put Map     Since am parsing a JSON  the arraylist increases in significant size  now my question is how do you get the values from both map keys in the arraylist   i have tried this    if  list isEmpty          list is an ArrayList              for int k   0  k  lt  list size    k                     map    HashMap list get k                                     Log d TAG   map size is    map size              String    keys   new String map size             String    date value   new String map size              String    value values   new String map size              int i   0          Set entries   map entrySet            Iterator iterator   entries iterator             while iterator hasNext                  Map Entry mapping    Map Entry iterator next                keys i    mapping getKey   toString                 date value i    map get keys i                 if keys i  equals DATE                    date value i    map get keys i                   else if keys i  equals VALUE                    value values i    map get keys i                                      i                         But i can t seem to get all the values  the Map size always return a value of 2  which is just the elements  how can i get all the values from the Map keys in the ArrayList  Thanks

User · Answer

Suppose I have Hashmap with key datatype as KeyDataType and value datatype as ValueDataType

HashMap<KeyDataType,ValueDataType> list;

Add all items you needed to it. Now you can retrive all hashmap keys to a list by.

KeyDataType[] mKeys;
mKeys=list.keySet().toArray(new KeyDataType[list.size()]);

So, now you got your all keys in an array mkeys[]

you can now retrieve any value by calling

 list.get(mkeys[position]);

User · Answer

Try it this way     I am considering the HashMap with key and value of type String  HashMap lt String String gt   HashMap lt String String gt  hmap   new HashMap lt String String gt      hmap put  key1   Val1    hmap put  key2   Val2     ArrayList lt String gt  arList   new ArrayList lt String gt      for Map Entry lt String String gt  map   hmap entrySet           arList add map getValue

User · Answer

List constructor accepts any data structure that implements Collection interface to be used to build a list   To get all the keys from a hash map to a list   Map lt String  Integer gt  map   new HashMap lt String  Integer gt     List lt String gt  keys   new ArrayList lt  gt  map keySet       To get all the values from a hash map to a list   Map lt String  Integer gt  map   new HashMap lt String  Integer gt     List lt Integer gt  values   new ArrayList lt  gt  map values

User · Answer

Java 8 solution for produce string like  key1  value1 key2  value2       private static String hashMapToString HashMap lt String  String gt  hashMap         return hashMap keySet   stream                map  key  - gt  key          hashMap get key                collect Collectors joining             and produce a list simple collect as list  private static List lt String gt  hashMapToList HashMap lt String  String gt  hashMap         return hashMap keySet   stream                map  key  - gt  key          hashMap get key                collect Collectors toList

User · Answer

Why do you want to re-invent the wheel  when you already have something to do your work  Map keySet   method gives you a Set of all the keys in the Map   Map lt String  Integer gt  map   new HashMap lt String  Integer gt      for  String key  map keySet          System out println  key       key       System out println  value       map get key        Also  your 1st for-loop looks odd to me  -     for int k   0  k  lt  list size    k                 map    HashMap list get k          You are iterating over your list  and assigning each element to the same reference - map  which will overwrite all the previous values   All you will be having is the last map in your list   EDIT  -  You can also use entrySet if you want both key and value for your map  That would be better bet for you  -      Map lt String  Integer gt  map   new HashMap lt String  Integer gt          for Entry lt String  Integer gt  entry  map entrySet              System out println entry getKey             System out println entry getValue             P S   -  Your code looks jumbled to me  I would suggest  keep that code aside  and think about your design one more time  For now  as the code stands  it is very difficult to understand what its trying to do

User · Answer

It has method to find all values from map  Map lt K  V gt  map getMapObjectFromXyz    Collection lt V gt  vs  map values           Iterate over vs to do some operation

User · Answer

This is incredibly old  but I stumbled across it trying to find an answer to a different question      my question is how do you get the values from both map keys in the arraylist    for  String key   map keyset        list add key         map get key           the Map size always return a value of 2  which is just the elements   I think you may be confused by the functionality of HashMap  HashMap only allows 1 to 1 relationships in the map   For example if you have   String TAG FOO    FOO   String TAG BAR    BAR     and attempt to do something like this   ArrayList lt String gt  bars   ArrayList lt  gt   bar   Bar   bAr   baR    HashMap lt String String gt  map   new HashMap lt  gt     for  String bar   bars      map put TAG BAR  bar       This code will end up setting the key entry  BAR  to be associated with the final item in the list bars   In your example you seem to be confused that there are only two items  yet you only have two keys recorded which leads me to believe that you ve simply overwritten the each key s field multiple times

User · Answer

Put i   somewhere at the end of your loop    In the above code  the 0 position of the array is overwritten because i is not incremented in each loop   FYI  the below is doing a redundant search   if keys i  equals DATE                        date value i    map get keys i                    else if keys i  equals VALUE                     value values i    map get keys i                      replace with   if keys i  equals DATE                        date value i    mapping getValue      else if keys i  equals VALUE                     value values i    mapping getValue        Another issue is that you are using i for date value and value values  This is not valid unless you intend to have null values in your array

User · Answer

Create an ArrayList of String type to hold the values of the map  In its constructor call the method values   of the Map class  Map  lt String  Object gt  map  List lt Object gt  list   new ArrayList lt Object gt  map values

[java] Retrieve all values from HashMap keys in an ArrayList Java

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