How to add HashMap to ArrayList

Question

Can someone please tell me why the code below overwrites every element in the ArrayList with the most recent entry into the ArrayList? Or how to correctly add new elements of hashmaps to my ArrayList?

ArrayList<HashMap<String, String>> prodArrayList = new ArrayList<HashMap<String, String>>();

HashMap<String, String> prodHashMap = new HashMap<String, String>();

public void addProd(View ap)
{
    // test arraylist of hashmaps
    prodHashMap.put("prod", tvProd.getText().toString());

    prodArrayList.add(prodHashMap);

    tvProd.setText("");

    // check data ///

    Log.e("myLog","Data prodArrayList in ADD Method Size = "+prodArrayList.size());

    for(int i=0; i< prodArrayList.size();i++)
    {
         Log.e("myLog","Data prodArrayList in ADD Method = "+prodArrayList.get(i).toString());
    }
}

Rod_Algonquin · Accepted Answer · 2014-08-13 18:06:48Z

19

problem:

prodHashMap.put("prod", tvProd.getText().toString());

You are using the same key each time you are adding an element to the the arraylist with the same reference to the HashMap thus changing its values.

Solution:

create a new instance of HashMap each time you want to add it to the ArrayList to avoid changing its values upon calling addProd

public void addProd(View ap)
{
    // test arraylist of hashmaps
    HashMap<String, String> prodHashMap = new HashMap<String, String>();
    prodHashMap.put("prod", tvProd.getText().toString());

    prodArrayList.add(prodHashMap);

    tvProd.setText("");

    // check data ///

    Log.e("myLog","Data prodArrayList in ADD Method Size = "+prodArrayList.size());

    for(int i=0; i< prodArrayList.size();i++)
    {
         Log.e("myLog","Data prodArrayList in ADD Method = "+prodArrayList.get(i).toString());
    }
}

answered Aug 13, 2014 at 18:06

Rod_Algonquin

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1 Comment

AhabLives Over a year ago

I see. I get it now. Thank you for the explanation. I will mark as correct in ten min. Thanks again.

f.khantsis · Accepted Answer · 2019-02-23 20:15:11Z

0

This is for adding multiple maps to List

Map<String,Object> map1=new HashMap<>();
map1.  // add required items

Map<String,Object> map2=new HashMap<>();
map2.  // add required items

Map<String,Object> map3=new HashMap<>();
map3.  // add required items

List<String,Object> list=new ArrayList<>();

list.add(map1);

list.add(map2);

list.add(map3);

edited Feb 23, 2019 at 20:15

f.khantsis

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answered Feb 23, 2019 at 16:53

umamaheshwar g

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1 Comment

pragman Over a year ago

use 4 spaces at the beginning of any line of code to format your code better

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