diff -r 576e7a2861ae -r 369903afbb29 src/main/java/de/uapcore/sudoku/DocumentHandler.java
--- a/src/main/java/de/uapcore/sudoku/DocumentHandler.java	Sat Jul 25 14:01:28 2020 +0200
+++ b/src/main/java/de/uapcore/sudoku/DocumentHandler.java	Sat Jul 25 15:29:51 2020 +0200
@@ -32,12 +32,18 @@
 
 /**
  *
- * @author mike
  */
 public class DocumentHandler {
     
     private String filename;
-    
+
+    /**
+     * Loads data into the specified field.
+     *
+     * @param field the field to populated with the loaded data
+     * @throws IOException if loading fails or no file name has been set before
+     * @see #setFilename(String)
+     */
     public void load(Field field) throws IOException {
         if (!isFilenameSet()) {
             throw new IOException("no filename supplied");
@@ -72,7 +78,14 @@
         }
         field.setAllCellsModified(false);
     }
-    
+
+    /**
+     * Saves the specified field to a file.
+     *
+     * @param field the field to save
+     * @throws IOException if saving fails or the file name has not been set before
+     * @see #setFilename(String)
+     */
     public void save(Field field) throws IOException {
         if (!isFilenameSet()) {
             throw new IOException("no filename supplied");
@@ -89,15 +102,28 @@
             }
         }
     }
-    
+
+    /**
+     * Sets the file name for loading and saving data.
+     *
+     * @param filename the file name
+     */
     public void setFilename(String filename) {
         this.filename = filename;
     }
-    
+
+    /**
+     * Clears the file name.
+     */
     public void clearFilename() {
         filename = null;
     }
-    
+
+    /**
+     * Checks whether a file name has been set.
+     *
+     * @return true if a file name is known, false otherwise
+     */
     public boolean isFilenameSet() {
         return filename != null;
     }