try

ArrayList<HashMap<String, String>> test = new ArrayList<HashMap<String, String>>();
HashMap<String, String> n = new HashMap<String, String>();
n.put("a", "a");
n.put("b", "b");
test.add(n);

HashMap<String, String> m = test.get(0);//it will get the first HashMap Stored in array list 

String strArr[] = new String[m.size()];
int i = 0;
for (HashMap<String, String> hash : test) {
    for (String current : hash.values()) {
        strArr[i] = current;
        i++;
    }
}

Your code is nota completed so I can't know what is test an thearchive. But let's create an example:

HashMap<String, ArrayList<String>> list = new HashMap<String, ArrayList<String>>();
ArrayList<String> anotherlist = new ArrayList<String>();
anotherlist.add("Brazil");
anotherlist.add("USA");
list.put("Augusto", anotherlist);

I hope it helps.

Always try to use interface reference in Collection, this adds more flexibility.
What is the problem with the below code?

List<Map<String,List<String>>> list = new ArrayList<Map<String,List<String>>>();//This is the final list you need
Map<String, List<String>> map1 = new HashMap<String, List<String>>();//This is one instance of the  map you want to store in the above list.
List<String> arraylist1 = new ArrayList<String>();
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.

I think what you need is a Map of Map of List.ie.,

Map< String, Map< String, List< String>>>

Sample code below:

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class Test {
public static void main(String[] args) throws IOException {

    Map<String,Map<String,List<String>>> scheduleMap=new HashMap<>();

    //Adding
    addSchedule(scheduleMap, "1111", "Engineering", "Tue3");
    addSchedule(scheduleMap, "1111", "Engineering", "Wed2");
    addSchedule(scheduleMap, "1111", "Math", "Wed4");
    addSchedule(scheduleMap, "1111", "Physics", "Fri10");
    addSchedule(scheduleMap, "2222", "Engineering", "Wed2");
    addSchedule(scheduleMap, "2222", "Chemistry ", "Wed4");

    //Printing
    printSchedule(scheduleMap);

}

private static void printSchedule(Map<String, Map<String, List<String>>> scheduleMap) {
    //Sample printing
    for(Entry<String, Map<String, List<String>>> staff : scheduleMap.entrySet()) {
        for(Entry<String,List<String>> subject:staff.getValue().entrySet()) {
            StringBuilder sb=new StringBuilder();
            sb.append(staff.getKey()).append(" : ").append(subject.getKey()).append(" : ");
            for(String sessionTime: subject.getValue()) {
                sb.append(sessionTime).append(", ");
            }
            sb.setLength(sb.length()-2);
            System.out.println(sb.toString());
        }
    }
}

public static void addSchedule(Map<String,Map<String,List<String>>> scheduleMap, String id,String subject,String sessionTime) {
    if(!scheduleMap.containsKey(id)) {
        scheduleMap.put(id, new HashMap<String,List<String>>());
    }
    if(!scheduleMap.get(id).containsKey(subject)) {
        scheduleMap.get(id).put(subject, new ArrayList<String>());
    }
    scheduleMap.get(id).get(subject).add(sessionTime);
}
}

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

Given...

public ArrayList<HashMap<String, String>> xmlFileNames = new ArrayList<>();

then something like this should do it.

HashMap<String, String> nhm = new HashMap<>();
for (HashMap xmlFileHm : xmlFileNames ) {
  nhm.putAll(xmlFileHm);
}

but be aware if you have duplicate keys in your hashmaps they will get overwritten.

You should also think about coding to interfaces. Take a look at Map and List rather than typing your collections to implementations (ArrayList and HashMap). Take a look at this thread which is quite interesting What does it mean to "program to an interface"?

Depending on what you are trying to do as well you might consider a MultiMap as this might server your purposes better

Edit After update to the question...

A multimap would be better here with one key and multiple values. Although arguably if the key never changes then you could just store the values in a list. For multiamps you can use Google's guava library or do one yourself. For example (not checked for compilation errors as Im doing this from my head)

Map<String, List<String>> m = new HashMap<>();
if (m.containsKey("key")) {
   m.get("key").add("new value");
}
else {
  List<String> l = new ArrayList<>();
  l.add("new value");
  m.put("key", l);
}

Try this way,hope this will help you to solve your problem.

public class PendingAdapter extends BaseAdapter {

    private List<Map<String, Object>> mPendingItemList;

    public PendingAdapter() {
        mPendingItemList = DataModel.getInstance().getPendingItemList();
    }

    @Override
    public int getCount() {
        return mPendingItemList.size();
    }

    @Override
    public Object getItem(int position) {
        return mPendingItemList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (null == convertView) {

            convertView = LayoutInflater.from(getActivity()).inflate(
                    R.layout.pending_item, null);
            holder = new ViewHolder();

            holder.tv_title = (TextView) convertView
                    .findViewById(R.id.pi_tv_title);
            holder.tv_content = (TextView) convertView
                    .findViewById(R.id.pi_tv_content);
            holder.tv_counter = (TextView) convertView
                    .findViewById(R.id.pi_tv_counter);
            holder.tv_ongoing = (TextView) convertView
                    .findViewById(R.id.pi_tv_ongoing);
            holder.tv_type = (TextView) convertView
                    .findViewById(R.id.pi_tv_type);
            holder.tv_date = (TextView) convertView
                    .findViewById(R.id.pi_tv_date);
            convertView.setTag(holder);
        }else {
            holder = (ViewHolder) convertView.getTag();
        }

        @SuppressWarnings("unchecked")
        HashMap<String, String> itemDataHashMap = (HashMap<String, String>) getItem(position);

        holder.tv_title.setText(itemDataHashMap.get("planet"));
        holder.tv_content.setText(itemDataHashMap.get("content"));
        holder.tv_counter.setText(itemDataHashMap.get("counter"));
        holder. tv_type.setText(itemDataHashMap.get("type"));
        holder.tv_ongoing.setText(itemDataHashMap.get("ongoing"));
        holder.tv_date.setText(itemDataHashMap.get("date"));

        convertView.setTag(holder);
        return convertView;
    }

    static class ViewHolder {
        TextView tv_title;
        TextView tv_content;
        TextView tv_counter;
        TextView tv_ongoing;
        TextView tv_type;
        TextView tv_date;
    }
}