How to write an ArrayList of Strings into a text file?

Question

I want to write an ArrayList<String> into a text file.

The ArrayList is created with the code:

ArrayList arr = new ArrayList();

StringTokenizer st = new StringTokenizer(
    line, ":Mode set - Out of Service In Service");

while(st.hasMoreTokens()){
    arr.add(st.nextToken());    
}

Hickey

What's your desired output for this input? – Manzanares

You code looks like it is reading a text file into an array. Is that what you actually mean? – Frond

my code is reading a file and then tokenize it and store those tokens in an arraylist. now i want to write this arraylist into a file. – Hickey

The answers all assume a different type of output. Can you give an example of how you want the output to look (or does it just need to be readable?) – Frond

@kathy: I was trying to write this arraylist in a text file. Anyways, I have done that already with the help of Andrey's code. Thanks for replying. – Hickey

Answer 1

import java.io.FileWriter;
...
FileWriter writer = new FileWriter("output.txt"); 
for(String str: arr) {
  writer.write(str + System.lineSeparator());
}
writer.close();

Politics

define your array as: ArrayList<String> arr = new ArrayList<String>(); – Politics

what do you meann by arr? – Syringomyelia

it's the name of the variable that holds reference to array – Politics

Where exactly would output.txt be situated in this case? Internal storage? - i.e. how to retrieve this file? – Pisano

in current working directory (i.e. directory from which you started your java program) – Politics

Answer 2

Java NIO

You can do that with a single line of code nowadays using Java NIO.

Create the arrayList and the Path object representing the file where you want to write into:

Path out = Paths.get("output.txt");
List<String> arrayList = new ArrayList<> ( Arrays.asList ( "a" , "b" , "c" ) );

Create the actual file, and fill it with the text in the ArrayList by calling on java.nio.file.Files utility class.

Files.write(out,arrayList,Charset.defaultCharset());

Consonant

what is Files, what package is it from? – Physicality

java.nio.file.Files, standard Java class since 1.7 – Englis

Nice and simple. – Infeasible

Answer 3

I would suggest using FileUtils from Apache Commons IO library.It will create the parent folders of the output file,if they don't exist.while Files.write(out,arrayList,Charset.defaultCharset()); will not do this,throwing exception if the parent directories don't exist.

FileUtils.writeLines(new File("output.txt"), encoding, list);

Dulcie

Answer 4

If you need to create each ArrayList item in a single line then you can use this code

private void createFile(String file, ArrayList<String> arrData)
            throws IOException {
        FileWriter writer = new FileWriter(file + ".txt");
        int size = arrData.size();
        for (int i=0;i<size;i++) {
            String str = arrData.get(i).toString();
            writer.write(str);
            if(i < size-1)**//This prevent creating a blank like at the end of the file**
                writer.write("\n");
        }
        writer.close();
    }

Dropkick

What if you open the same file and continue writing to it? I think have the last newline character is useful. – Hipped

Yes it will be useful for append mode. Just comment the if condition and will work fine. – Dropkick

Answer 5

If you want to serialize the ArrayList object to a file so you can read it back in again later use ObjectOuputStream/ObjectInputStream writeObject()/readObject() since ArrayList implements Serializable. It's not clear to me from your question if you want to do this or just write each individual item. If so then Andrey's answer will do that.

Nicolle

I just want to add each item to a file but its showing an error message of incompatible type. – Hickey

Answer 6

You might use ArrayList overloaded method toString()

String tmp=arr.toString();
PrintWriter pw=new PrintWriter(new FileOutputStream(file));
pw.println(tmp.substring(1,tmp.length()-1));

Nonetheless

Answer 7

I think you can also use BufferedWriter :

BufferedWriter writer = new BufferedWriter(new FileWriter(new File("note.txt")));

String stuffToWrite = info;

writer.write(stuffToWrite);

writer.close();

and before that remember too add

import java.io.BufferedWriter;

Levania

This answer literally has nothing to do with ArrayLists of Strings, which is what the original poster was asking about. – Longshore

@Kaiser Keister But all that's needed is to convert the ArrayLIst to a String which is easy to do in a loop with StringBuilder? – Inch

Answer 8

Write a array list to text file using JAVA

public void writeFile(List<String> listToWrite,String filePath) {

    try {
        FileWriter myWriter = new FileWriter(filePath);
        for (String string : listToWrite) {
            myWriter.write(string);
            myWriter.write("\r\n");
        }
        myWriter.close();
        System.out.println("Successfully wrote to the file.");
    } catch (IOException e) {
        System.out.println("An error occurred.");
        e.printStackTrace();
    }
}

Lactic

Are you affiliated with the site? How is this better or worse than the other answers here? – Bluma

Answer 9

    FileWriter writer = new FileWriter("output.txt");
    Arrays.asStream(arr.stream()
            .forEach(i -> {
                try{
                        writer.write(i + ",");
                }
                catch (Exception e){}
                        
            }));
    writer.close();

Spectatress