diff --git a/.idea/checkstyle-idea.xml b/.idea/checkstyle-idea.xml
index cec0567..7fbdf32 100644
--- a/.idea/checkstyle-idea.xml
+++ b/.idea/checkstyle-idea.xml
@@ -8,6 +8,7 @@
     <option name="thirdPartyClasspath" />
     <option name="activeLocationIds">
       <option value="bundled-google-checks" />
+      <option value="bundled-sun-checks" />
     </option>
     <option name="locations">
       <list>
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
new file mode 100644
index 0000000..4723b7e
--- /dev/null
+++ b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverter.java
@@ -0,0 +1,81 @@
+package edu.ntnu.idi.idatt2003.g40.mappe;
+
+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 {
+
+  /**
+   * 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>}
+   *
+   * @throws IllegalArgumentException if stock object(s) cannot be converted.
+   *
+   * */
+  public List<Stock> getStocksFromStrings(final List<String> validStocks) {
+
+    List<Stock> stocksFromFile = new ArrayList<>();
+    List<String> stockSymbols = new ArrayList<>();
+
+    validStocks.forEach(s -> {
+      String[] lineElements = s.split(",");
+      String stockSymbol = lineElements[0].trim();
+      String stockName = lineElements[1].trim();
+      BigDecimal stockPrice = new BigDecimal(lineElements[2].trim());
+
+      try {
+        Stock stockObject = new Stock(stockSymbol, stockName, stockPrice);
+        if (!stockSymbols.contains(stockSymbol)) {
+          stockSymbols.add(stockSymbol);
+          stocksFromFile.add(stockObject);
+        }
+      } catch (IllegalArgumentException e) {
+        System.err.println("(" + s + ") is not a valid stock! Skipping...");
+      }
+
+    });
+    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
new file mode 100644
index 0000000..d0d0279
--- /dev/null
+++ b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParser.java
@@ -0,0 +1,184 @@
+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);
+        return true;
+      } catch (NumberFormatException e) {
+        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) {
+      this.rule = rule;
+    }
+  }
+
+  /**
+   * 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 {
+    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 -> {
+        String[] parts = s.trim().split(",");
+
+        if (parts.length != 3) {
+          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());
+
+        return validCode && validName && validPrice;
+      }).toList();
+
+    } catch (IOException e) {
+      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);
+    }
+  }
+}
diff --git a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Main.java b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Main.java
index b835759..186a1ba 100644
--- a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Main.java
+++ b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Main.java
@@ -1,17 +1,18 @@
 package edu.ntnu.idi.idatt2003.g40.mappe;
 
-//TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or
-// click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.
+import java.io.IOException;
+import java.util.List;
+
 public class Main {
   static void main() {
-    //TIP Press <shortcut actionId="ShowIntentionActions"/> with your caret at the highlighted text
-    // to see how IntelliJ IDEA suggests fixing it.
-    IO.println(String.format("Hello and welcome!"));
-
-    for (int i = 1; i <= 5; i++) {
-      //TIP Press <shortcut actionId="Debug"/> to start debugging your code. We have set one <icon src="AllIcons.Debugger.Db_set_breakpoint"/> breakpoint
-      // for you, but you can always add more by pressing <shortcut actionId="ToggleLineBreakpoint"/>.
-      IO.println("i = " + i);
+    FileParser parser1 = new FileParser("src/main/resources/dummydata.txt");
+    FileConverter converter1 = new FileConverter();
+    try {
+      List<Stock> stocksInFile = converter1.getStocksFromStrings(parser1.readFile());
+      parser1.writeStocksToFile(converter1.stocksToStrings(stocksInFile));
+      stocksInFile.forEach(s -> System.out.println(s.getSymbol()));
+    } catch (IOException e) {
+      System.err.println(e.getMessage());
     }
   }
 }
diff --git a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Stock.java b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Stock.java
index 6f433a1..9e44c68 100644
--- a/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Stock.java
+++ b/src/main/java/edu/ntnu/idi/idatt2003/g40/mappe/Stock.java
@@ -1,5 +1,6 @@
 package edu.ntnu.idi.idatt2003.g40.mappe;
 
+import java.io.IOException;
 import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.Comparator;
@@ -50,7 +51,7 @@ public Stock(final String symbol,
    *
    * @return the stock symbol
    */
-  public String getSymbol() {
+ public String getSymbol() {
     return symbol;
   }
 
@@ -129,5 +130,4 @@ public BigDecimal getLatestPriceChange() {
 
     return currentPrice.subtract(previousPrice);
   }
-
 }
diff --git a/src/main/resources/dummydata.txt b/src/main/resources/dummydata.txt
new file mode 100644
index 0000000..25144a3
--- /dev/null
+++ b/src/main/resources/dummydata.txt
@@ -0,0 +1,14 @@
+#THIS IS A COMMENT.
+
+AAPL, Apple Inc., 276.43
+NVID, Nvidida Corporation, 241.591
+
+#Above me are some valid formats.
+#Below me are some invalid formats
+
+COOLI, This is a cool name, 252.2
+
+COOL, This is a cool name, 252.2a
+
+AAPL,Apple Inc.,276.43
+NVID,Nvidida Corporation,241.591
\ No newline at end of file
diff --git a/src/main/resources/testStockData.txt b/src/main/resources/testStockData.txt
new file mode 100644
index 0000000..b349d0e
--- /dev/null
+++ b/src/main/resources/testStockData.txt
@@ -0,0 +1,11 @@
+#THIS IS A COMMENT.
+
+AAPL, Apple Inc., 276.43
+NVID, Nvidida Corporation, 241.591
+
+#Above me are some valid formats.
+#Below me are some invalid formats
+
+COOLI, This is a cool name, 252.2
+
+COOL, This is a cool name, 252.2a
\ No newline at end of file
diff --git a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverterTest.java b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverterTest.java
new file mode 100644
index 0000000..6404d78
--- /dev/null
+++ b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/FileConverterTest.java
@@ -0,0 +1,74 @@
+package edu.ntnu.idi.idatt2003.g40.mappe;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.math.BigDecimal;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class FileConverterTest {
+
+  private FileConverter converter;
+
+  private String validStockAsString1;
+  private String validStockAsString2;
+  private String validStockAsString3;
+  private ArrayList<String> allStocks;
+  private String invalidStockAsString1;
+
+  @BeforeEach
+  void setUp() {
+    validStockAsString1 = "AAPL, Apple inc., 251.42";
+    validStockAsString2 = "NVID, Nvidia corp., 100.25";
+    validStockAsString3 = "SAMS, Samsung corporation, 103.21";
+
+    invalidStockAsString1 = "INVALID, This stock has an invalid code!, 100.21";
+
+    allStocks = new ArrayList<>();
+
+    allStocks.add(validStockAsString1);
+    allStocks.add(validStockAsString2);
+    allStocks.add(validStockAsString3);
+    allStocks.add(invalidStockAsString1);
+
+    converter = new FileConverter();
+  }
+
+  @Test
+  void converter_returns_valid_stock_apple() {
+
+    boolean stockIncluded = false;
+
+    List<Stock> stocksFromConverter = converter.getStocksFromStrings(allStocks);
+
+    for (Stock s : stocksFromConverter) {
+      if (s.getSymbol().equals("AAPL")) {
+        stockIncluded = true;
+        break;
+      }
+    }
+
+    Assertions.assertTrue(stockIncluded);
+  }
+
+  @Test
+  void converter_ignores_invalid_stock_representation() {
+
+    boolean stockIncluded = false;
+
+    List<Stock> stocksFromConverter = converter.getStocksFromStrings(allStocks);
+
+    for (Stock s : stocksFromConverter) {
+      if (s.getSymbol().equals("INVALID")) {
+        stockIncluded = true;
+        break;
+      }
+    }
+
+    Assertions.assertFalse(stockIncluded);
+  }
+}
\ No newline at end of file
diff --git a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParserTest.java b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParserTest.java
new file mode 100644
index 0000000..2935a30
--- /dev/null
+++ b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/FileParserTest.java
@@ -0,0 +1,60 @@
+package edu.ntnu.idi.idatt2003.g40.mappe;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class FileParserTest {
+
+  private final String testStockDataPath = "src/main/resources/testStockData.txt";
+  FileParser fileParser;
+
+  private final String validStockFromFile = "NVID, Nvidida Corporation, 241.591";
+
+  private final String invalidStockFromFile = "COOLI, This is a cool name, 252.2";
+
+  private final String commentFromFile = "#Above me are some valid formats.";
+
+  private List<String> allLines = new ArrayList<>();
+
+  private List<String> validStocks = new ArrayList<>();
+
+  @BeforeEach
+  void setUp() throws Exception {
+    fileParser = new FileParser(testStockDataPath);
+    Path path = Paths.get(testStockDataPath);
+    allLines = Files.readAllLines(path);
+    try {
+      validStocks = fileParser.readFile();
+    } catch (Exception _) {
+      throw new Exception("Test failed");
+    }
+  }
+
+  @Test
+  void parser_gets_valid_stock_from_file() {
+    assertTrue(allLines.contains(validStockFromFile));
+    assertTrue(validStocks.contains(validStockFromFile));
+  }
+
+  @Test
+  void parser_skips_comments_from_file() {
+    assertTrue(allLines.contains(commentFromFile));
+    assertFalse(validStocks.contains(commentFromFile));
+  }
+
+  @Test
+  void parser_skips_invalid_stock_from_file() {
+    assertTrue(allLines.contains(invalidStockFromFile));
+    assertFalse(validStocks.contains(invalidStockFromFile));
+  }
+}
\ No newline at end of file
diff --git a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/StockTest.java b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/StockTest.java
index 1aaa672..9fa9f1a 100644
--- a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/StockTest.java
+++ b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/StockTest.java
@@ -74,7 +74,6 @@ void getHistoricalPricesGetsAllPrices() {
     boolean historicalPricesContainBothValues = historicalPrices.contains(new BigDecimal("100.00"))
             && historicalPrices.contains(new BigDecimal("200.00"));
 
-
     assertTrue(historicalPricesContainBothValues);
   }
 
diff --git a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/TransactionTest.java b/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/TransactionTest.java
deleted file mode 100644
index bc0b909..0000000
--- a/src/test/java/edu/ntnu/idi/idatt2003/g40/mappe/TransactionTest.java
+++ /dev/null
@@ -1,3 +0,0 @@
-public class TransactionTest {
-    
-}