W3Schools Tryit Editor

import java.io.FileOutputStream;
import java.io.IOException;
public class Main {
 public static void main(String[] args) {
 try {
 FileOutputStream output = new FileOutputStream("filename.txt");
 output.write("Hello".getBytes());
 output.close(); // must close manually
 System.out.println("Successfully wrote to the file.");
 } catch (IOException e) {
 System.out.println("Error writing file.");
 }
 }
}