Java Append input to File

Question

my teacher got me this exercise to create a calculator which can store operations to a file and read them out later. I got the writer and I got the calculator; but the writer somehow overwrites everything in the file instead of adding. I tried bufferedWrtier append and now I am trying the Printwriter.

Debugging shows that my list is getting filled properly; yet the result is, that the saved file only contains the last input number and the last input operator.

public class Rechnung {
static Scanner scanner = new Scanner(System.in);
static double zahl1, zahl2, ergebnis;
static String op;
static boolean abbruch = true;
static File fileName = new File("Therme.txt");
static String numbers1;
static String eingabe;

public static void eingabe() {

    while (abbruch) {
        System.out.println("Geben Sie eine Zahl ein: ");
        Listen.numbersDouble.add(scanner.nextDouble());
        System.out.println("Bitte entscheiden Sie sich für '+', '-', '/', '*', '=': ");
        op = scanner.next();
        Listen.operators.add(op);

        if (op.equals("=")) {
            for (int i = 0; i < Listen.operators.size(); i++)
            {
            Writer.write(String.valueOf(Listen.numbersDouble.get(i)), Listen.operators.get(i));
            }
            abbruch = false;

        }

        else {
        }

    }
    System.out.println(ausgabe());
}

public static double rechnen(String op, double zahl1, double zahl2)

{

    switch (op) {
    case "+":
        ergebnis = zahl1 + zahl2;
        return ergebnis;
    case "-":
        ergebnis = zahl1 - zahl2;
        return ergebnis;
    case "/":
        ergebnis = zahl1 / zahl2;
        return ergebnis;
    case "*":
        ergebnis = zahl1 * zahl2;
        return ergebnis;
    }
    return ergebnis;
}

public static double ausgabe() {

    zahl1 = Listen.numbersDouble.get(0);

    for (int i = 1; i <= Listen.numbersDouble.size(); i++)

    {
        op = Listen.operators.get(i - 1);

        if(op.equals("=")) 
                {
            return zahl1;
                }
        zahl2 = Listen.numbersDouble.get(i);
        zahl1 = Rechnung.rechnen(op, zahl1, zahl2);


    }
    return -80085;
}

}

public class Writer {

public static void write(String string, String op) {
final String FILENAME = "C:\\Users\\nowackan\\eclipse-workspace\\Test.txt"; {


    BufferedWriter bw = null;
    FileWriter fw = null;

    try {

        fw = new FileWriter(FILENAME);
        bw = new BufferedWriter(fw);
        PrintWriter out = new PrintWriter(bw);
        out.println(String.valueOf(string));
        out.println(op);


        System.out.println("Done");

    } catch (IOException e) {

        e.printStackTrace();

    } finally {

        try {

            if (bw != null)
                bw.close();

            if (fw != null)
                fw.close();

        } catch (IOException ex) {

            ex.printStackTrace();

        }

    }

}

}

Please note that I have barely a few weeks of programming experience and do not know any programming conventions.

Possible duplicate of [Trouble with filewriter overwriting files instead of appending to the end](https://stackoverflow.com/questions/10804286/trouble-with-filewriter-overwriting-files-instead-of-appending-to-the-end) — Rob, Nov 21 '18 at 13:43

Ryuzaki L · Accepted Answer · 2018-11-21T13:51:19.377

2

To append content to an existing file, open file writer in append mode by passing second argument as true.

 fw = new FileWriter(FILENAME,true);
 bw = new BufferedWriter(fw);
 PrintWriter out = new PrintWriter(bw);
 out.println(String.valueOf(string));
 out.println(op);

edited Nov 21 '18 at 13:51

answered Nov 21 '18 at 13:42

Ryuzaki L

37,302
12
68
98

score 2 · Answer 2 · answered Nov 21 '18 at 13:43

2

You need to use the constructor of FileWriter(File, boolean append) in your Writer class.

answered Nov 21 '18 at 13:43

Krzysztof Cichocki

6,294
1
16
32

score 2 · Answer 3 · answered Nov 21 '18 at 13:55

2

You need to use the "append" parameter in the Filewriter constructor, which the valued must be true.

FileWriter fwr = new FileWriter(FILEN,true);

answered Nov 21 '18 at 13:55

score 1 · Answer 4 · answered Nov 21 '18 at 13:51

Use this constructor instead of the one you are using to create the FileWriter, new FileWriter(FILENAME, true);

This is the java doc for this constructor and please read the append parameter of it,

/**
 * Constructs a FileWriter object given a file name with a boolean
 * indicating whether or not to append the data written.
 *
 * @param fileName  String The system-dependent filename.
 * @param append    boolean if <code>true</code>, then data will be written
 *                  to the end of the file rather than the beginning.
 * @throws IOException  if the named file exists but is a directory rather
 *                  than a regular file, does not exist but cannot be
 *                  created, or cannot be opened for any other reason
 */

Java Append input to File

4 Answers4