将值从一个Arraylist复制到另一个时，所有值均设置为在第一个Arraylist中输入的最后一个值

Question

I am having some issue writing a small program for myself. I have a class that will read from a CSV and put the data into arraylist of the class Farts (this is short for fighting arts before you ask). This works, when I test my output I can see the values read in from the csv.

 AssetManager assetManager =context.getAssets();
    ArrayList<Farts> arrayfarts = new ArrayList<Farts>();
    InputStream csvStream = null;
    System.out.println("right before try loop");

    try {
        csvStream = assetManager.open("farts.txt");
        InputStreamReader csvStreamReader = new InputStreamReader(csvStream);
        CSVReader csvreader = new CSVReader(csvStreamReader);
        Farts fdata = new Farts();
        String[] line;
        int temp=0;
        while ((line=csvreader.readNext())!=null){
            System.out.println("inside of while");
            fdata.fname=line[0];
            fdata.description=line[1];
            arrayfarts.add(temp,fdata);
            System.out.println("Array iteration " + temp + " of " + arrayfarts.size());
            System.out.println(arrayfarts.get(temp).fname + " " + arrayfarts.get(temp).description + "\n");
            temp++;
        }

    } catch (IOException e) {
        e.printStackTrace();
        System.out.println("ioexception"+e.toString());
    }
    return arrayfarts;
}

Back in my Main class I then use .addall to add what is returned from above. However the data in the Arraylist is populated by only the last value entered into it.

arrayFarts.addAll(readcsv.retrieveFarts(this));
    System.out.println(arrayFarts.get(0).fname + " " + arrayFarts.get(0).description + "\n");
    int temp=0;
        while (temp<arrayFarts.size()){
            cupboard().withDatabase(db).put(arrayFarts.get(temp));
            System.out.println("Array iteration " + temp + " of " + arrayFarts.size());
            System.out.println(arrayFarts.get(temp).fname+" "+arrayFarts.get(temp).description+"\n");
            temp++;
         }

Am I missing something?

Answer 1

The problem lies in these lines:

 fdata.fname=line[0]; fdata.description=line[1]; arrayfarts.add(temp,fdata); 

You need to create a new Farts instance each loop, not change a single instance.

As it stands, you simply add the same instance multiple times to the list, while changing its values. This means that you will see only the last parsed values after the loop completes. You will also see it multiple times, as ArrayList allows duplicates.