java: Store HashMap<String, String> in ArrayList<Object>

Question

ArrayList<Object> parameters = new ArrayList<Object>();

HashMap<String, String> parameter = new HashMap<String, String>();
parameter.put("key", "value");

parameters.add(parameter);
parameters.add((String) "additionalData"); //this line is here for a reason
destinationFunction(parameters);

....

destinationFunction(ArrayList<Object> data){
     HashMap<String, String> imported = (HashMap<String, String>) data.get(0);
     String value = imported.get("key");
}

How do i achieve this? When i try i receive no errors up until like 2 of destinationFunction where i receive null pointer exception

would that prevent parameters.add("additionalData"); as the ArrayList is now of a specific object? — Simon.
– Simon., Commented May 1, 2015 at 9:00
alternative solution would be to use JSON Objects and arrays. — nafas
– nafas, Commented May 1, 2015 at 9:08

user4853610 · Accepted Answer · 2015-05-01 09:07:40Z

1

ArrayList<Object> parameters = new ArrayList<Object>();

relpace this line with what you want to store in array list like you want to store hash map then create arraylist of type hash map

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

hope this will help you

answered May 1, 2015 at 9:07

user4853610

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Comments

nafas · Accepted Answer · 2015-05-01 11:59:47Z

0

Alternative Solution would be using JsonObject and JsonArrays. they are perfect for such "scenarios" (working with String,Integer and etc with combination of List and Map).

they may also be useful for complex object(e.g. working with Images) but will be abit more difficult to implement. in such cases please refer to java_serialization

in your case use JSONArray instead of your ArrayList and JsonObject instead of HashMap.

edited May 1, 2015 at 11:59

answered May 1, 2015 at 11:24

nafas

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1 Comment

Simon. Over a year ago

This solution solves the exact problem described in the question, where as implementing just an ArrayList of HashMap<String, String> would omit the single string value also contained in the ArrayList.

amodkanthe · Accepted Answer · 2015-05-01 09:01:07Z

0

use array list of hashmap

ArrayList<HashMap<String, String>>()

answered May 1, 2015 at 9:01

amodkanthe

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Comments

Paresh · Accepted Answer · 2015-05-01 09:06:39Z

0

Try to put ArrayList<HashMap<String, String>> instead of ArrayList<Object>

create a HashMap and add into the ArrayList. For Example:-

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

HashMap<String, String> map = new HashMap<>();
map.put("KEY", "VALUE");

list.add(map); //Add the map into list

answered May 1, 2015 at 9:06

Paresh

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Comments

antonpp · Accepted Answer · 2015-05-01 09:09:20Z

0

You did not specified what type are you storing in your arrayList. But you assume in your destinationFunction that this list contains only HashMap<String, String> elements. Besides terrible code style it is okay in java to write so. But you made a mistake when put in your arrayList an element of type String which is breaking your assumptions in destinationFunction.

P.S. Try to write more type safe code and avoid generic types with Object type parameter.

answered May 1, 2015 at 9:09

antonpp

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