将文件中的值添加到带有Map的HashMap中

Question

I'm trying to read from a package of txt files and adding the values to my HashMap. I'm trying to split the values using split(","). Then depending if the gender value is F or M to add to the right Map.

girlsByYear.put(number, (name, value)); This code gives me a compile error saying "The Field String.value is not visible", which I don't understand because it seems to be able to see number and name. I'm also new to using HashMaps and other sorts of Sets. I'm not even sure if that is the right syntax to put values into a map inside of a HashMap.

These are the HashMaps I'm using:

HashMap<String, Map<String, Integer>> girlsByYear = new HashMap<String, Map<String, Integer>>();
HashMap<String, Map<String, Integer>> boysByYear = new HashMap<String, Map<String, Integer>>();

public void load() throws FileNotFoundException {

    File dir = new File("src/data");
    File [] files = dir.listFiles();

    // for each file in the directory...
    for (File f : files)
    {   
        Scanner input = new Scanner(f);
        while (input.hasNext()) {

              String line = input.next();
              String [] details = line.split(",");

              String name = details[0];
              String gender = details[1];
              String value = details[2];

              if(gender == "F") {
                  girlsByYear.put(number, (name, value));
              }
              else {
                  boysByYear.put(number, (name, value));
              }

            }

        number++;

    }
}

Answer 1

First you need to check if the nested map exists and if not, create it. Then you can add the value by retrieving the nested map and putting an object inside of that map. eg:

if (!girlsByYear.containsKey(number)) {
    girlsByYear.put(number, new HashMap<>());
}
girlsByYear.get(number).put(name, value);

Answer 2

I want to improve @flake answer, if you use Java 8 you can you this:

girlsByYear.putIfAbsent(number, new HashMap<>());
girlsByYear.get(number).put(name, value);

Or you can try Guava library (a widely used library from Google), it has a data structure called Table:

Table<String, String, Integer> girlsByYear = HashBasedTable.create();
//...
girlsByYear.put(number, name, value);

You can check tutorial how to use Table here https://www.baeldung.com/guava-table