You need to iterate over your list, here is an example

public static void main(String[] args){
    List<LinkedHashMap<String,String>> list = new ArrayList<LinkedHashMap<String, String>>();

    LinkedHashMap<String, String> test = new LinkedHashMap<String, String>();
        test.put("a","1");
        test.put("b","2");

    list.add(test);

    for(Map<String, String> map : list){
        for(String key : map.keySet()){
            System.out.println("key: " + key + " value " + map.get(key));
        }
    }

}

No - you're storing them as a list, which isn't designed to be accessed by "key" - it doesn't have any notion of a key.

It sounds like really you want something like a Map<String, String> - assuming you only need to store a single value for each key.

If you're stuck with the ArrayList (and I'd at least change the parameter type to List, if not Iterable given that that's all you need) then what you've got is fine.

The first time onChildAdded is called, there will be an exception because arraylist will only have 1 item, and you are accessing index 2 that requires 3 or more items in the list.

String specificIndexValue = arraylist.get(2);

We will need more info to solve your question it prints one value four times which lie on index "1".

It seems you might want to store in an ordered map instead of an array, with the key being the snapshot key and the value being the snapshot.

Try this to debug...

@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {

    //add keys to arraylist
    String key=dataSnapshot.getKey();
    arraylist.add(key);

    if (arraylist.size() == 3){
       Log.i("Key: " arraylist.get(2), "Index: 2");
    }
}

1. You create marks outside the loop, so the same ArrayList is being used, only ONE, you need to create a new one at each iteration.

   Also prefer Integer.parseInt(sc.nextLine()) as sc.nextInt() because of newlines you don't want to handle correctly (that is what causes empty name in your output)

    for (int j = 0; j < 2; j++) {
        System.out.print("\nEnter name " + j + " = ");
        String name = sc.nextLine();
        marks = new ArrayList<>();
        for (int i = 0; i < 3; i++) {
            System.out.print("Enter marks " + i + " = ");
            marks.add(Integer.parseInt(sc.nextLine()));
        }
        marksTable.put(name, marks);
    }
   

2. For printing, take a look at How to iterate a Map and

    Map<String, List<Integer>> marksTable = Map.of(
            "name1", Arrays.asList(1, 2, 3),
            "name2", Arrays.asList(4, 5, 6),
            "name3", Arrays.asList(7, 8, 9)
    );
   
    System.out.println("---------------------");
    for (Map.Entry<String, List<Integer>> entry : marksTable.entrySet()) {
        String values = entry.getValue().stream().map(Object::toString).collect(Collectors.joining(" | "));
        System.out.println("| " + entry.getKey() + " | " + values + " |");
    }
    System.out.println("---------------------");
   

Also prefer more generic definitions, Map instead of HashMap, List instead of ArrayList, for the definition, for the instanciation keep classes

Map<String, List<Integer>> marksTable = new HashMap<>();
List<Integer> marks;

I don't understand why you are creating a List of maps. A Map will let you put several key value pairs. Here is a way that would work:

protected Map<String, String> yaml_parse(BufferedReader filename) throws IOException{
    String result;
    Map<String, String> map = new HashMap<String, String>();
    while ((result = filename.readLine()) != null) {
        //keyValue[0] = key, keyValue[1] = value
        String[] keyValue = result.split(": "); 
        map.put(keyValue[0], keyValue[1]);
    }

    return map;
}

And you would use it like this:

Map<String, String> map = yaml_parse("myFile.yaml");
String key1Value = map.get("key1"); //Stores key1's value into key1Value

I think you might be using the wrong data structure. From your question, it seems like you want a Map only, not a List of Maps.

I guess thats what you want to do

Map<String, List<String>> map = new HashMap<String, List<String>>();
// ...some more code...
for (List<String> regexNumbers : map.values()) {
    // regexNumbers is the value
}

Since you dont use the key in your method.

But your code whould be much more readable if you create a class - thats your structure, thats what you want, and you know (!) whats in it (even in a few years):

class CountryNumbers {
    String country;
    List<String> numbers;
}

Examplecode to print every number to a country:

List<CountryNumbers> list = fillListSomehow();
for (CountryNumbers countryNumbers : list) {
    String country = countryNumbers.country;
    System.out.println("The regexes for country " + country + " are: ");
    for (String regexNumber : countryNumbers.numbers) {
        System.out.println("  " + regexNumber);
    }
}