How to read from a file and save to variables in Java

Question

I’m having difficulties, because in a file manipulation exercise in Java, the teacher asked us to create a program that takes the name and note 1 and note 2 of two proofs and store in a txt file as follows: name;Nota1;nota2 only that later in another exercise he asks to read from the file the data and calculate the media of the notes saving again the data in another file in the following form name;Nota1;nota2;media, as I do this reading and save the data in variable String,float, float again ???

public class LeitorComun extends Leitor {
    private String nome;
    private  double n1,n2,media;
    String linha;

    public LeitorComun(FileInputStream arquivo) {
        super(arquivo);
    }


     @Override
    public void ler() throws IOException{
        InputStreamReader isr = new InputStreamReader(this.arquivo);
        BufferedReader br = new BufferedReader(isr);
        do{
        this.linha = br.readLine();
              if(this.linha != null){
                  String [] palavras = this.linha.split(";");
                  System.out.println("nova linha ------------------------------------");
                  for(int i =0; i<palavras.length;i++){
                      System.out.println("palavra lida: "+ palavras[i]);
                  }
              }
          }while(this.linha != null);

    }
}

Answer 1

You can create a simple method for converting String for double:

private double converter(String texto) {
  return Double.parseDouble(texto);
}

And change your method ler for:

@Override
public void ler() throws IOException {
  InputStreamReader isr = new InputStreamReader(this.arquivo);
  BufferedReader br = new BufferedReader(isr);

  do {
    this.linha = br.readLine();

    if (this.linha != null) {
      double nota1;
      double nota2;
      double media;

      try {
        String[] palavras = this.linha.split(";");
        System.out.println("nova linha ------------------------------------");
        nota1 = this.converter(palavras[1]);
        nota2 = this.converter(palavras[2]);
        media = (nota1 + nota2) / 2;
        System.out.println(palavras[0] + "/ Média: " + media);
      } catch (NumberFormatException ex) {
        System.out.println("A linha \"" + this.linha + "\" contém erros");
      }
    }
  } while (this.linha != null);
}

With the following file notas.txt:

Joseph;10;9

Andrew;5;8

The result is:

nova linha ------------------------------------
José/ Média: 9.5
nova linha ------------------------------------
André/ Média: 6.5