diff --git a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverter.java b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverter.java
index 936a9d4..6075200 100644
--- a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverter.java
+++ b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverter.java
@@ -1,23 +1,73 @@
 package edu.ntnu.idi.idatt2003.g40.mappe;
 
-import java.io.IOException;
 import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Converts stock objects to/from string format for file handling.
+ *
+ * <p style ="font-weight: bold;">Responsibilities:</p>
+ * <ul>
+ *   <li>Turn a valid list of stock string elements to a
+ *   list of {@link Stock} objects.</li>
+ *
+ *   <li>Turn a list of stock objects to a
+ *     list of string elements.</li>
+ * </ul>
+ *
+ * <p>Used with {@link FileParser}</p>
+ *
+ * @see FileParser
+ * @author tohja
+ * @version 1.0.0
+ *
+ * */
 public class FileConverter {
 
-  public List<Stock> getStocksFromFile(FileParser fileParser) throws IOException {
-    List<String> strings = fileParser.readFile();
+  /**
+   * Turns a list of valid string representations
+   * of stock objects to a list of stock objects.
+   *
+   * @param validStocks list of string elements properly
+   *                    representing stock objects.
+   *
+   * @return {@link List<Stock>}
+   * */
+  public List<Stock> getStocksFromStrings(final List<String> validStocks) {
     List<Stock> stocksFromFile = new ArrayList<>();
+    List<String> stockSymbols = new ArrayList<>();
 
-    strings.forEach(s -> {
+    validStocks.forEach(s -> {
       String[] lineElements = s.split(",");
       String stockSymbol = lineElements[0].trim();
       String stockName = lineElements[1].trim();
       BigDecimal stockPrice = new BigDecimal(lineElements[2].trim());
-      stocksFromFile.add(new Stock(stockSymbol, stockName, stockPrice));
+      // TODO: try-catch
+      Stock stockObject = new Stock(stockSymbol, stockName, stockPrice);
+      if (!stockSymbols.contains(stockSymbol)) {
+        stockSymbols.add(stockSymbol);
+        stocksFromFile.add(stockObject);
+      }
     });
     return stocksFromFile;
   }
+
+  /**
+   * Converts a list of stocks to string representations of that stock.
+   *
+   * <p>format: SYMBOL, NAME, PRICE</p>
+   *
+   * @param stocks a list of {@link Stock} objects.
+   *
+   * @return a list of string representation of the stock objects.
+   * */
+  public List<String> stocksToStrings(final List<Stock> stocks) {
+    ArrayList<String> stringList = new ArrayList<>();
+    stocks.forEach(s ->
+            stringList.add(s.getSymbol().trim() + "," + s.getCompany().trim()
+                    + "," + s.getSalesPrice().toString())
+    );
+    return stringList;
+  }
 }
diff --git a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParser.java b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParser.java
index 23c8f8a..d0d0279 100644
--- a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParser.java
+++ b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParser.java
@@ -1,23 +1,74 @@
 package edu.ntnu.idi.idatt2003.g40.mappe;
 
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
 import java.io.IOException;
 import java.math.BigDecimal;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
 import java.util.List;
 import java.util.function.Predicate;
 
+/**
+ * Class used to parse (filter) valid stocks from a .txt file.
+ *
+ * <p style ="font-weight: bold;">Responsibilities:</p>
+ * <ul>
+ *   <li>Read file and return a filtered list of string elements,
+ *   where each element represents a valid stock line.</li>
+ *
+ *   <li>Write a list of string representations of stock objects
+ *   to file, each stock separated by a line.</li>
+ * </ul>
+ *
+ * <p>Used with {@link FileConverter}</p>
+ *
+ * @see FileConverter
+ * @author tohja
+ * @version 1.0.0
+ * */
 public class FileParser {
 
+  /** The path name this parser is using.*/
   private final String pathName;
 
+  /**
+   * Rule set for validating lines and strings.
+   *
+   * <p>Uses predicates.</p>
+   * */
   private enum ParserRuleSet {
+
+    /**
+     * Rule for whether string is empty or not.
+     * */
     NOT_EMPTY(s -> !s.trim().isEmpty()),
+
+    /**
+     * Rule for if string is comment or not.
+     * */
     NOT_COMMENT(s -> !s.startsWith("#")),
+
+    /**
+     * Rule for if line is in valid format.
+     * */
     VALID_FORMAT(NOT_EMPTY.rule.and(NOT_COMMENT.rule)),
+
+    /**
+     * Rule for if string is considered a valid company symbol.
+     * */
     VALID_CODE(s -> s.matches("[A-Z]{4}")),
+
+    /**
+     * Rule for if string is a valid company name.
+     * */
     VALID_NAME(s -> s.matches(".*")),
+
+    /**
+     * Rule for if string can be parsed to a {@link BigDecimal} object.
+     * */
     CAN_PARSE_TO_BIG_DECIMAL(s -> {
       try {
         new BigDecimal(s);
@@ -26,9 +77,20 @@ private enum ParserRuleSet {
         return false;
       }
     }),
+
+    /**
+     * Rule for if string is in a valid price format.
+     * */
     VALID_PRICE_FORMAT(s -> s.matches("[^a-zA-Z]+")),
+
+    /**
+     * Rule for if string is a valid price.
+     * */
     VALID_PRICE(VALID_PRICE_FORMAT.rule.and(CAN_PARSE_TO_BIG_DECIMAL.rule));
 
+    /**
+     * The constants' rules as predicates with input of type string.
+     * */
     private final Predicate<String> rule;
 
     ParserRuleSet(final Predicate<String> rule) {
@@ -36,15 +98,35 @@ private enum ParserRuleSet {
     }
   }
 
+  /**
+   * Constructor.
+   *
+   * @param pathName the file path name to read.
+   * */
   public FileParser(final String pathName) {
     this.pathName = pathName;
   }
 
+  /**
+   * Reads the file and returns a list element of all valid stocks as strings.
+   *
+   * <p>Uses {@link BufferedReader} for opening a file stream. </p>
+   *
+   * @return {@link List<String>} object of all valid stock strings in file.
+   *
+   * @throws IOException if path cannot be read.
+   *
+   * @see Path
+   * */
+
   public List<String> readFile() throws IOException {
-    try {
-      Path path = Paths.get(pathName);
-      List<String> allLines = Files.readAllLines(path);
-      List<String> readableLines = allLines.stream().filter(ParserRuleSet.VALID_FORMAT.rule).toList();
+    Path path = Paths.get(pathName);
+    try (BufferedReader bufferedReader = Files.newBufferedReader(path)) {
+
+      List<String> allLines = bufferedReader.readAllLines();
+      List<String> readableLines =
+              allLines.stream()
+                      .filter(ParserRuleSet.VALID_FORMAT.rule).toList();
 
       // Valid lines (following the correct regular expressions)
       return readableLines.stream().filter(s -> {
@@ -54,9 +136,14 @@ public List<String> readFile() throws IOException {
           return false;
         }
 
-        boolean validCode = ParserRuleSet.VALID_CODE.rule.test(parts[0].trim());
-        boolean validName = ParserRuleSet.VALID_NAME.rule.test(parts[1].trim());
-        boolean validPrice = ParserRuleSet.VALID_PRICE.rule.test(parts[2].trim());
+        boolean validCode = ParserRuleSet
+                .VALID_CODE.rule.test(parts[0].trim());
+
+        boolean validName = ParserRuleSet
+                .VALID_NAME.rule.test(parts[1].trim());
+
+        boolean validPrice = ParserRuleSet
+                .VALID_PRICE.rule.test(parts[2].trim());
 
         return validCode && validName && validPrice;
       }).toList();
@@ -65,4 +152,33 @@ public List<String> readFile() throws IOException {
       throw new IOException("File parser could not parse file!");
     }
   }
+
+  /**
+   * Writes a given lists of stocks to the file.
+   *
+   * <p>Uses {@link BufferedWriter}.</p>
+   *
+   * @param stringList list of strings representing stocks in the format
+   *                   SYMBOL, NAME, PRICE
+   *
+   * @throws IOException if writing process throws error.
+   * */
+  public void writeStocksToFile(final List<String> stringList)
+          throws IOException {
+    Path path = Paths.get(pathName);
+
+    try (BufferedWriter writer = Files.newBufferedWriter(path,
+            StandardOpenOption.CREATE,
+            StandardOpenOption.APPEND)) {
+
+      writer.newLine();
+
+      for (String line : stringList) {
+        writer.write(line);
+        writer.newLine();
+      }
+    } catch (IOException e) {
+      throw new IOException("Error during buffered write", e);
+    }
+  }
 }