Write ArrayList to textfile

Question

Does anyone know the best way to use the Formatter method to write an ArrayList? An example of code would be much appreciated to get me on the right track! I've never used the Formatter method before so i'm a little new to it and how to use it and an ArrayList at the same time!

Answer 1

This example is not simple, it uses generics which you would not encounter early in java learning (use it at your own risk :) ).

package javaformatterexample;

import java.util.Formatter;
import java.util.List;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Arrays;

public class TextFileFormatter<T>
{

    Formatter formatter;
    String    format;
    public TextFileFormatter(Formatter formatter, String format)
    {
        this.formatter = formatter;
        this.format    = format   ;
    }

    public Formatter getFormatter()
    {
        return formatter;
    }

    public String getFormat()
    {
        return format;
    }

    public void writeList(List<T> list)
    {
        for (T element : list)
        {
            getFormatter().format(getFormat(),element);
        }        
    }

    public void close()
    {
        getFormatter().close();
    }

    public static void main(String[] args)
    {
        System.out.println("Shows how to use the class Formatter");
        try
        {   
            File file = new File("out.txt");
            //formatter that writes doubles to a file
            TextFileFormatter<Double> formatter = new TextFileFormatter<>(
                    new Formatter(file), "%f");
            // writes a list of doubles
            formatter.writeList(Arrays.asList(2.0, 2.1, -15.3));
            formatter.close();
        }
        catch (FileNotFoundException e)
        {
            System.out.println("File not found");
        }
    }

}