How can I store HashMap String ArrayList String inside a list

Question

My hashmap stores the string as key and arraylist as the values  Now  I need to embed this into a list  That is  it will be of the following form   List lt HashMap lt String  ArrayList lt String gt  gt  gt    These are the declarations I have used   Map lt String  ArrayList lt String gt  gt  map   new HashMap lt String  ArrayList lt String gt  gt     ArrayList lt String gt  arraylist   new ArrayList lt String gt     map put key arraylist   List lt String gt  list   new ArrayList lt String gt       Can anyone help me which method and how to use in the list to proceed storing my map into it

User · Answer

class Student        instance variable or data members       Map lt Integer  List lt Object gt  gt  mapp   new HashMap lt Integer  List lt Object gt  gt         Scanner s1   new Scanner System in       String name   s1 nextLine        int regno       int mark1      int mark2      int total      List lt Object gt  list   new ArrayList lt Object gt         mapp put regno list     what wrong in this part      list add mark1       list add mark2           String mark2 mapp get regno  2

User · Answer

First  let me fix a little bit your declaration   List lt Map lt String  List lt String gt  gt  gt  listOfMapOfList        new HashList lt Map lt String  List lt String gt  gt  gt       Please pay attention that I used concrete class  HashMap  only once  It is important to use interface where you can to be able to change the implementation later    Now you want to add element to the list  don t you  But the element is a map  so you have to create it   Map lt String  List lt String gt  gt  mapOfList   new HashMap lt String  List lt String gt  gt       Now you want to populate the map  Fortunately you can use utility that creates lists for you  otherwise you have to create list separately   mapOfList put  mykey   Arrays asList  one    two    three       OK  now we are ready to add the map into the list   listOfMapOfList add mapOfList     BUT   Stop creating complicated collections right now  Think about the future  you will probably have to change the internal map to something else or list to set etc  This will probably cause you to re-write significant parts of your code  Instead define class that contains you data and then add it to one-dimentional collection   Let s call your class Student  just as example    public Student       private String firstName      private String lastName      private int studentId       private Colectiuon lt String gt  courseworks   Collections emtpyList           constructors  getters  setters etc     Now you can define simple collection   Collection lt Student gt  students   new ArrayList lt Student gt       If in future you want to put your students into map where key is the studentId  do it   Map lt Integer  Student gt  students   new HashMap lt Integer  Student gt

User · Answer

Try the following   List lt Map lt String  ArrayList lt String gt  gt  gt  mapList        new ArrayList lt Map lt String  ArrayList lt String gt  gt  gt     mapList add map     If your list must be of type List lt HashMap lt String  ArrayList lt String gt  gt  gt   then declare your map variable as a HashMap and not a Map

User · Answer

Always try to use interface reference in Collection  this adds more flexibility  What is the problem with the below code   List lt Map lt String List lt String gt  gt  gt  list   new ArrayList lt Map lt String List lt String gt  gt  gt      This is the final list you need Map lt String  List lt String gt  gt  map1   new HashMap lt String  List lt String gt  gt      This is one instance of the  map you want to store in the above list  List lt String gt  arraylist1   new ArrayList lt String gt     arraylist1 add  Text1     And so on   map1 put  key1  arraylist1     And so on    list add map1    In this way you can add    You can easily do it like the above

User · Answer

First you need to define the List as    List lt Map lt String  ArrayList lt String gt  gt  gt  list   new ArrayList lt  gt       To add the Map to the List   use add E e  method    list add map

[java] How can I store HashMap<String, ArrayList<String>> inside a list?

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