How to Write an Arraylist of Strings into a Text File

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

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

How to write an ArrayList into a text file in Android App

You can use google gson.

    class Four {
    String first,second;
    int third,fourth;
    public Four()
    {

    }
}
 //save_array(your_context,"MyData.txt",your_array)
void save_array(Context contxt,String file_name,ArrayList<Four> testes)
{
    Gson gson = new Gson();
    String json = gson.toJson(testes);
    String root = contxt.getExternalFilesDir(null).getAbsolutePath() + "/arrays";

    File file = new File(root);
    file.mkdirs();
    try {
        File out_file = new File(file, file_name);
        if(out_file.exists()){
            out_file.delete();
        }
        FileWriter writer = new FileWriter(out_file,true);
        writer.append(json);
        writer.flush();
        writer.close();
    }catch (Exception ex)
    {

    }
}
ArrayList<Four> saved_array(Context contxt, String file_name) throws IOException {
    String path = contxt.getExternalFilesDir(null).getAbsolutePath() + "/arrays/"+file_name;

    Gson gson = new Gson();
    BufferedReader br = new BufferedReader(new FileReader(path));
    return gson.fromJson(br, new TypeToken<List<Four>>(){}.getType());

}

you can call as
Remember to request for storage permissions

Insert line by line data in txt file with arraylist

Use :

outStream.write(contactsinformations.get(i) + "\n");

Here \n signifies the new line.

Writing into text file from ArrayList that has multiple values per ArrayList object (java)

BufferedWriter has a newLine() method, you may use that if you declare output as a BufferedWriter .

private static void saveFile(ArrayList<Vehicle> vehs){
    File fileName = new File("VehicleList.txt"); 

    try {
        FileWriter fw = new FileWriter(fileName);
        BufferedWriter output = new BufferedWriter(fw);

        for (int i = 0; i < vehs.size(); i++){
            output.write(vehs.get(i).toString());
            output.newLine();
        }

        output.close();

    } catch (Exception e) {
        JOptionPane.showMessageDialog(null, "I cannot create that file");
    }
}

Also for the javadoc of the method :

Writes a line separator. The line separator string is defined by the
system property line.separator, and is not necessarily a single
newline ('\n') character.

Saving ArrayList to Text File

There are two changes:

Your class need to implement CharSequence to be eligible to be passed to Files.write.

You need to over-ride toString method to specify how your contents look like when saved.
I can see output after above two changes.

    class Animals implements CharSequence {

        public int id;
        public String type, vertebrate, aclass;

public Animals(int id,String type,String vertebrate,String aclass) {
this.id = id;
this.type = type;
this.vertebrate = vertebrate;
            this.aclass = aclass;
        }

        public int getID() {
            return id;
        }

        public String getType() {
            return type;
        }

        public String getVert() {
            return vertebrate;
        }

        public String getaclass() {
            return aclass;
        }

        @Override
        public int length() {
            return toString().length();
        }

        @Override
        public char charAt(int index) {
            return toString().charAt(index);
        }

        @Override
        public CharSequence subSequence(int start, int end) {
            return toString().subSequence(start, end);
        }

        /* (non-Javadoc)
         * @see java.lang.Object#toString()
         */
        @Override
        public String toString() {
            return "Animals [id=" + id + ", type=" + type + ", vertebrate=" + vertebrate + ", aclass=" + aclass + "]";
        }

        }