Java/libGDX barebones dialog text input and selection with simple validation, hacked together

gistfile1.txt

import javax.swing.JOptionPane;
import javax.swing.UIManager;

public class GUI {
  public static final String DEFAULT_CHOOSE_TITLE = "Selection";
  public static final String DEFAULT_CHOOSE_MSG = "Please choose:";
  public static final String DEFAULT_INPUT_TITLE = "Input";
  
  public static final int PLAIN_MESSAGE = JOptionPane.PLAIN_MESSAGE;
  public static final int ERROR_MESSAGE = JOptionPane.ERROR_MESSAGE;
  public static final int INFO_MESSAGE = JOptionPane.INFORMATION_MESSAGE;
  public static final int WARNING_MESSAGE = JOptionPane.WARNING_MESSAGE;
  public static final int QUESTION_MESSAGE = JOptionPane.QUESTION_MESSAGE;

  public static final String CHARS_UPPERCASE =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZÄÜÖ";
  public static final String CHARS_LOWERCASE =
    "abcdefghijklmnopqrstuvwxyzäüö";
  public static final String CHARS_ALPHABET =
    CHARS_UPPERCASE + CHARS_LOWERCASE;
  public static final String CHARS_NUM =
    "0123456789";
  public static final String CHARS_ALPHANUMERIC =
    CHARS_ALPHABET + CHARS_NUM;
  public static final String CHARS_SPECIAL =
    "!§$%&/()=?+-_.,;><|^°'#{[]}´`²³\\";
  public static final String CHARS_ALPHA_SPECIAL =
    CHARS_ALPHANUMERIC + CHARS_SPECIAL;
  
  public GUI() {
    switchToNativeLookAndFeel();
  }
  
  public void switchToNativeLookAndFeel() {
    try {
      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
    } catch (Exception e) {
      System.out.println("Error switching to native look and feel", e);
    }
  }
  
  public <T extends Object> T chooseUsingSystemPopup(final T[] choices) {
    return chooseUsingSystemPopup(
        DEFAULT_CHOOSE_MSG, DEFAULT_CHOOSE_TITLE,
        JOptionPane.PLAIN_MESSAGE, choices, choices[0]);
  }
  
  public <T extends Object> T chooseUsingSystemPopup(
      String msg, String title, final T[] choices) {
    return chooseUsingSystemPopup(
        msg, title, JOptionPane.PLAIN_MESSAGE, choices, choices[0]);
  }
  
  public <T extends Object> T chooseUsingSystemPopup(
      String msg, String title, int messageType,
      final T[] choices) {
    return chooseUsingSystemPopup(msg, title, messageType, choices, choices[0]);
  }
  
  @SuppressWarnings("unchecked")
  public <T extends Object> T chooseUsingSystemPopup(
      String msg, String title, int messageType,
      final T[] choices,
      T initialChoice) {
    return (T) JOptionPane.showInputDialog(null, msg, title, messageType,
                                           null, choices, initialChoice);
  }
  
  public String getStringUsingSystemPopup(String msg) {
    return getStringUsingSystemPopup(msg, DEFAULT_INPUT_TITLE, 0);
  }
  
  public String getStringUsingSystemPopup(String msg, String title) {
    return getStringUsingSystemPopup(msg, title, 0);
  }
  
  public String getStringUsingSystemPopup(String msg,
                                          String title,
                                          int messageType) {
    return JOptionPane.showInputDialog(null, msg, title, messageType);
  }
  
  public String getStringUsingSystemPopup(String msg,
                                          String title,
                                          int messageType,
                                          int minLength,
                                          int maxLength,
                                          String allowedChars,
                                          boolean cancelEnabled) {
    String val;
    while (true) {
      val = getStringUsingSystemPopup(msg, title, messageType);
      
      if (val == null) {
        if (cancelEnabled) {
          return null;
        }
        
        continue;
      }
      
      if (val.length() < minLength) {
        continue;
      }
      
      if (val.length() > maxLength) {
        continue;
      }
      
      if (allowedChars != null && allowedChars.length() > 0) {
        for (char aChar : val.toCharArray()) {
          if (allowedChars.indexOf(aChar) == -1) {
            continue;
          }
        }
      }
      
      return val;
    }
  }
}