Count distinct names saved in txt

Question

I have a txt file with a line-separated user name below:

diego
sergio
antonio
maria
diego
antonio

Notice that names can repeat, and I would like to count and list only the distinct names.

I did this method to list the entire file:

String strPath = DIRETORIO + ARQUIVO_FILE;
if (pathExists(strPath)) {
    List<String> texto = Files.readAllLines(new File(strPath).toPath());
    for (String linha : texto) {
        System.out.println(linha);
    }
} else {
    System.out.println("arquivo não existe");
}

but I’m not sure how to adapt it into another method that makes this count of different names. How do I count this?

Note: some names may come with a point separating type surname diego.felipe, but each name and/or surname is saved per line only.

Answer 1

You can use the collection HashSet, where elements are held uniquely. If you try to insert an existing element, it is not added.

The interesting thing about this collection is that the basic operations add, remove, contains and size have asymptotic complexity of O(1).

HashSet<String> nomes = new HashSet<String>();

String strPath = DIRETORIO + ARQUIVO_FILE;
if (pathExists(strPath)) 
{
    List<String> texto = Files.readAllLines(new File(strPath).toPath());
    for (String linha : texto) 
    {   
        nomes.add(linha);
    }

    System.out.println("Total de nomes: " + nomes.size());    

}
else 
{
    System.out.println("arquivo não existe");
}

Answer 2

Create a list of strings to save the names, validate if the name no longer exists inside the list before adding it, if it does not exist, add the name to the list. At the end of the iteration, use lista.size() to obtain the sum.

List<String> nomes = new ArrayList<String>();

String strPath = DIRETORIO + ARQUIVO_FILE;
if (pathExists(strPath)) 
{
    List<String> texto = Files.readAllLines(new File(strPath).toPath());
    for (String linha : texto) 
    {            
        if(!nomes.contains(linha)){
            nomes.add(linha);
        }
    }

    System.out.println("Total de nomes: " + nomes.size());    

}
else 
{
    System.out.println("arquivo não existe");
}

Answer 3

Look I don’t know how it works in Java. But in C# has a set called Hashset that does not keep repeated elements. In a way you will need to do something like this for Java.

HashSet<string> devedores = new HashSet<string>();
// Podemos adicionar elementos no conjunto utilizando o método Add
devedores.Add("victor");
devedores.Add("osni");

// Para sabermos o número de elementos adicionados, utilizamos a propriedade
// Count do conjunto. Nesse exemplo elementos guardará o valor 2
int elementos = devedores.Count;

// O conjunto não guarda elementos repetidos, então se tentarmos
// adicionar novamente a string "victor", o número de elementos
// continua sendo 2
devedores.Add("victor");

Answer 4

You can further simplify the solution with HashSet, passing to List read from the file directly to the constructor of the HashSet:

String strPath = DIRETORIO + ARQUIVO_FILE;
if (pathExists(strPath)) {
    Set<String> nomes = new HashSet<>(Files.readAllLines(new File(strPath).toPath()));
    System.out.println("Total de nomes: " + nomes.size());    
} else {
    System.out.println("arquivo não existe");
}