Save ArrayList<String> to text file

Question

longlat files:

101.2425101.2334103.345 

The coding have algorithm like this:

ArrayList<String> getDifferenceList(String filePath) {
    File f = new File("longlat.txt");

    String line, x1 = null, x2= null, x3 = null;

BufferedReader buffreader = null;

try {
    buffreader = new BufferedReader(new FileReader(f));
    while (( line = buffreader.readLine()) != null) {
        String[] parts = line.split("");
        x1 = (parts[0]);   
        x2 = (parts[1]);  
        x3 = (parts[2]); 
    }
} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

ArrayList<String> ret = new ArrayList<String>();
FileWriter writer;




if (x1 == null || x1.isEmpty()
        || x2 == null || x2.isEmpty()
        || x3 == null || x3.isEmpty()) {

    ret.add(x1);
    ret.add(x2);
    ret.add(x3);

    return ret;
}

int index = 0;

while (index < x1.length()
        && index < x2.length()
        && index < x3.length()) {
    if (x1.charAt(index) != x2.charAt(index)
            || x1.charAt(index) != x3.charAt(index)) {
        break;
    }
    index++;
}

ret.add(x1.substring(index, x1.length()));
ret.add(x2.substring(index, x2.length()));
ret.add(x3.substring(index, x3.length()));


return ret;


}

The values need to be stored into text file are inside the arraylist of ret.

I've tried :

FileWriter writer = new FileWriter("lalala.txt");
     for(String str: ret) {
        writer.write(str);         
      } writer.close();

I put the above coding at the top of :

ret.add(x1.substring(index, x1.length()));

Problem : Nothing shown when I click a button "Show lalala text".

and also tried :

 try {
      OutputStreamWriter out = new OutputStreamWriter(openFileOutput ("lalala.txt",MODE_APPEND));       
              String text =(ret);
              out.write(text);
              out.write('\n');             
              out.close();
                    } 
        catch (java.io.IOException e) {
        Toast.makeText(this,"Sorry Text could't be added",Toast.LENGTH_LONG).show
();}
                                   }

I put the above coding at the top of :

ret.add(x1.substring(index, x1.length()));

Problem : Error at 'ret'. It said "Type mismatch: cannot convert from ArrayList to String"

I don't know how to take the arraylist and stored them into text file. Please give me some ideas, thanks.

Answer 1

You are writing file before writing to your array List ret

    I put the above coding at the top of :
ret.add(x1.substring(index, x1.length()));

Your ret is empty before this line. Your if-condition evaluates true then it actually returns from there. if-condition evaluates false. then you have empty array list.

There fore write to file after you have fully filled your arrayList.

i.e. just before return statement.

  return ret;

Answer 2

ArrayList<String> cannot be cast to String.

You can write the content of the ArrayList to a file in this way:

PrintWriter out = null;
try {
    out = new PrintWriter(new FileWriter("lalala.txt"));
    for (String text : ret) {
        out.writeln(text);
    }             
} catch (IOException e) {
    System.err.println("Caught IOException: " +  e.getMessage());

} finally {
    if (out != null) {
        out.close();
    }
}