minor fixes

src/me/teridax/jcash/Logging.java

@@ -21,6 +21,10 @@ public final class Logging {
      * Folder the log files are stored in, relative to the file containing the class
      */
     private static final String LOG_FOLDER_NAME = "logs/";
+    /**
+     * Format for the date time used for log files
+     */
+    private static final String DATE_TIME_FORMAT = "yyyy-MM-dd_HH-mm-ss";
 
     /**
      * Initialize the global system logger.
@@ -35,17 +39,30 @@ public final class Logging {
         LOGGER.setLevel(level);
     }
 
+    /**
+     * Add a console log handler writing to the applications stderr
+     * @param level the level to set the handler to
+     */
     private static void createConsoleLogger(Level level) {
         var ch = new ConsoleHandler();
         ch.setLevel(level);
         LOGGER.addHandler(ch);
     }
 
+    /**
+     * Create a log handler writing to a file.
+     * The file will be located in a folder directly besides the application
+     * with the name LOG_FOLDER_NAME. The name will follow the format DATE_TIME_FORMAT plus "log" as
+     * file extension.
+     * @param level the log level to set the handler to
+     */
     private static void createFileLogger(Level level) {
+        // setup log file name
         var now = LocalDateTime.now();
-        var dateTime = DateTimeFormatter.ofPattern("yyyy-MM-dd_HH-mm-ss").format(now);
+        var dateTime = DateTimeFormatter.ofPattern(DATE_TIME_FORMAT).format(now);
         var logFileName = LOG_FOLDER_NAME + dateTime + ".log";
 
+        // setup the folder for the logs
         initializeLogFolder();
 
         try {
@@ -57,6 +74,10 @@ public final class Logging {
         }
     }
 
+    /**
+     * Checks if the folder containing log files is present.
+     * If the folder does not exist, the function will create a new folder.
+     */
     private static void initializeLogFolder() {
         var folderPath = Path.of(LOG_FOLDER_NAME);
 

src/me/teridax/jcash/Main.java

@@ -47,6 +47,13 @@ public final class Main {
         getInstance().showLoginScreen();
     }
 
+    /**
+     * Set the look and feel via the ui manager.
+     * This function will select a look and feel so that the application will
+     * look most like a native application.
+     * It will select the systems look and feel for Windows and MacOS
+     * and GTK for unix based systems.
+     */
     private static void setPlatformDependingTheme() {
         // default look and feel
         var laf = UIManager.getCrossPlatformLookAndFeelClassName();

src/me/teridax/jcash/gui/Loader.java

@@ -2,7 +2,6 @@ package me.teridax.jcash.gui;
 
 import me.teridax.jcash.Logging;
 import me.teridax.jcash.banking.management.BankingManagementSystem;
-import me.teridax.jcash.lang.Translator;
 
 import javax.swing.*;
 import javax.swing.filechooser.FileNameExtensionFilter;

src/me/teridax/jcash/gui/login/AccountSelectionListener.java

@@ -5,6 +5,7 @@ import me.teridax.jcash.banking.management.Profile;
 /**
  * Listens for changes in a selected account.
  */
+@FunctionalInterface
 public interface AccountSelectionListener {
 
     /**

src/me/teridax/jcash/gui/login/LoginView.java

@@ -1,14 +1,22 @@
 package me.teridax.jcash.gui.login;
 
 import javax.swing.*;
-import javax.swing.text.NumberFormatter;
+import javax.swing.text.*;
 import java.awt.*;
 import java.text.NumberFormat;
 
+import static java.awt.BorderLayout.NORTH;
+import static javax.swing.SwingConstants.CENTER;
 import static me.teridax.jcash.lang.Translator.translate;
 
 public class LoginView extends JPanel {
 
+    /**
+     * Maximum number of decimal digits that can be stored lossless by a 32-bit signed integer.
+     * N = log10(2^32-1) = 9,632959861146281
+     */
+    private static final int MAX_PIN_DECIMAL_DIGITS = 9;
+
     private JFormattedTextField blz;
     private JFormattedTextField iban;
     private JPasswordField pin;
@@ -25,7 +33,7 @@ public class LoginView extends JPanel {
         this.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));
         this.setLayout(new BorderLayout(16, 16));
         this.add(new JScrollPane(content), BorderLayout.CENTER);
-        this.add(new JLabel(translate("Cashmachine")), BorderLayout.NORTH);
+        this.add(new JLabel("<html><h1>" + translate("Cashmachine") + "</b></html>", CENTER), NORTH);
 
         var constraints = new GridBagConstraints();
 
@@ -49,6 +57,26 @@ public class LoginView extends JPanel {
         this.iban = new JFormattedTextField(getNumberFormat());
         this.pin = new JPasswordField();
         this.login = new JButton(translate("Login"));
+
+        restrictPasswordToDigits();
+    }
+
+    /**
+     * Adds a document filter onto {@link #pin} that filters out everything that is not a digit.
+     * The filter also restricts the amount of digits that can be entered to {@link #MAX_PIN_DECIMAL_DIGITS}
+     */
+    private void restrictPasswordToDigits() {
+        ((AbstractDocument) this.pin.getDocument()).setDocumentFilter(new DocumentFilter() {
+            @Override
+            public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs)
+                    throws BadLocationException {
+                String newText = fb.getDocument().getText(0, fb.getDocument().getLength()) + text;
+
+                if (newText.matches(String.format("\\d{1,%s}", MAX_PIN_DECIMAL_DIGITS))) {
+                    super.replace(fb, offset, length, text, attrs);
+                }
+            }
+        });
     }
 
     private NumberFormatter getNumberFormat() {

src/me/teridax/jcash/gui/transfer/TransferData.java

@@ -20,12 +20,14 @@ public class TransferData {
      * @throws IllegalArgumentException if the bank or the account do not exist
      */
     public void transferValue(double amount, String blz, String ibanString) throws IllegalArgumentException {
+        // get bank to transfer to
         var bank = bms.getBank(blz);
         if (bank.isEmpty()) {
             Logging.LOGGER.warning("Bank not found: " + blz);
             throw new IllegalArgumentException("Bank not found: " + blz);
         }
 
+        // validate iban of target account
         var iban = 0;
         try {
              iban = StringDecoder.decodeUniqueIdentificationNumber(ibanString);
@@ -34,6 +36,7 @@ public class TransferData {
             throw new IllegalArgumentException("IBAN has invalid format: " + ibanString);
         }
 
+        // get account to transfer value to
         var account = bank.get().getAccount(iban);
         if (account.isEmpty()) {
             Logging.LOGGER.warning("Account not found: " + iban);

src/me/teridax/jcash/gui/transfer/TransferDialog.java

@@ -3,12 +3,14 @@ package me.teridax.jcash.gui.transfer;
 import me.teridax.jcash.Logging;
 import me.teridax.jcash.banking.accounts.Account;
 import me.teridax.jcash.banking.management.BankingManagementSystem;
-import me.teridax.jcash.lang.Translator;
 
 import static javax.swing.JOptionPane.ERROR_MESSAGE;
 import static javax.swing.JOptionPane.showMessageDialog;
 import static me.teridax.jcash.lang.Translator.translate;
 
+/**
+ * Dialog class for transferring some value from one account to another
+ */
 public class TransferDialog {
 
     private final Account account;
@@ -20,21 +22,21 @@ public class TransferDialog {
         this.account = account;
         this.onDeposit = onDeposit;
 
-        transferView = new TransferView();
+        this.transferView = new TransferView();
-        transferData = new TransferData(bms);
+        this.transferData = new TransferData(bms);
-        transferView.getTransfer().addActionListener(e -> transfer());
+        this.transferView.getTransfer().addActionListener(e -> transfer());
-        transferView.getCancel().addActionListener(e -> transferView.dispose());
+        this.transferView.getCancel().addActionListener(e -> transferView.dispose());
-        transferView.showDialog();
+        this.transferView.showDialog();
     }
 
     private void transfer() {
         try {
             var amount = transferView.getAmount();
 
-            account.takeoff(amount);
+            this.account.takeoff(amount);
-            transferData.transferValue(amount, transferView.getBlz(), transferView.getIban());
+            this.transferData.transferValue(amount, transferView.getBlz(), transferView.getIban());
-            onDeposit.run();
+            this.onDeposit.run();
-            transferView.dispose();
+            this.transferView.dispose();
         } catch (IllegalArgumentException ex) {
             Logging.LOGGER.severe("Could not transfer: " + ex.getMessage());
             showMessageDialog(null, translate("Invalid account"), translate("Could not transfer"), ERROR_MESSAGE);