Design Pattern Command for Switch java

I want to use design pattern for this switch - case code. I tried to use the command pattern, but I could not understand how(I was programming only 2 for months) I wrote this program to learn how to better program.

My code:

public class Server {
private static final String READ_NEW_MESSAGES = "read new mes";
private static final String SEND_PRIVATE_MESSAGES = "send mes";
private static final String JOIN_CHAT = "find chat";
private static final String CREATE_CHAT = "chating";
private static final String QUIT = "quit";
private static final String EXIT = "exit";
private static final String REGISTRATION = "reg";
private static final String CREATE_PRIVATE_CHAT = "priv chat";
private static final String CONNECT_TO_PRIVATE_CHAT = "connect pm";
private static final String START_CHAT = "Start";
private Populator<PrivateMessage> privateMessagePopulator;
private Populator<Registration> registrationPopulator;
private Populator<Message> messagePopulator;
private Populator<PrivateChat> privateChatPopulator;
private Populator<Chat> publicChatPopulator;
private List<PrivateMessage> privateMessages;
private BufferedReader reader;
private String currentUser;
private Set<String> users;
private static Logger log = Logger.getLogger(Server.class.getName());
private List<Chat> chats;
private String password;
private Set<Registration> registration;
private List<PrivateChat> pmChat;
private String chatName;

public Server() {
    server();
}

public void server() {
    reader = new BufferedReader(new InputStreamReader(System.in));
    privateMessages = new ArrayList<PrivateMessage>();
    users = new HashSet<String>();
    chats = new ArrayList<Chat>();
    privateMessagePopulator = new PrivateMessagePopulator();
    privateChatPopulator = new PrivateChatPopulator();
    publicChatPopulator = new PublicChatPopulator();
    messagePopulator = new MessagePopulator();
    registrationPopulator = new RegistratorPopulator();
    registration = new HashSet<Registration>();
    pmChat = new ArrayList<PrivateChat>();
}

public void start() {
    String decition = "";

    while (true) {
        try {
            registrationOrLogin();
        } catch (IOException e1) {
            e1.printStackTrace();
        }

        while (decition != QUIT) {

            System.out.println("Create a chat - chating");
            System.out.println("Join the chat - find chat");
            System.out.println("Send private message - send mes");
            System.out.println("Read new messages - new mes");
            System.out.println("Quit - quit");
            System.out.println("Create private chat - priv chat");
            System.out.println("Connect to private chat - connect pm");

            try {
                decition = reader.readLine();
                switch (decition) {
                case CREATE_PRIVATE_CHAT:
                    createPrivateChat();
                    break;
                case CREATE_CHAT:
                    createChat();
                    break;
                case JOIN_CHAT:
                    joinChat();
                    break;
                case SEND_PRIVATE_MESSAGES:
                    sendPrivateMessage();
                    break;
                case READ_NEW_MESSAGES:
                    showNewMessages();
                    break;
                case QUIT:
                    logout();
                    break;
                case REGISTRATION:
                    registration();
                    break;
                case CONNECT_TO_PRIVATE_CHAT:
                    joinToPrivateChat();
                    break;

                default:
                    break;
                }
            } catch (IOException e) {
                log.warning("Error while reading decition from keyboard. "
                        + e.getMessage());
            }
        }
    }
}

private void sendPrivateMessage() throws IOException {
    PrivateMessage privateMessage = privateMessagePopulator.populate();
    privateMessage.setSenderName(currentUser);
    privateMessages.add(privateMessage);
}

private void joinChat() throws IOException {
    System.out.println("Exist public chat");
    for (Chat chat : chats) {
        System.out.println(chat.getChatName());
    }
    System.out.println("Enter the name of chat you wish to join");
    chatName = reader.readLine();
    for (Chat chat : chats) {
        if (chatName.equals(chat.getChatName())) {
            for (Message mes : chat.getMessages()) {
                System.out.println(mes.getSenderName() + ": "
                        + mes.getContent());
            }
            publicComunication(chat);
        }
    }
}

private boolean hasNewMessages() {
    boolean result = false;
    for (PrivateMessage privateMessage : privateMessages) {
        if (currentUser.equals(privateMessage.getReceiverName())) {
            result = true;
        }
    }

    for (PrivateChat pm : pmChat) {
        if (pm.getAddUserName().equals(currentUser)) {
            result = true;
        }
    }
    return result;
}

private void showNewMessages() {
    if (hasNewMessages()) {
        for (PrivateMessage privateMessage : privateMessages) {
            if (currentUser.equals(privateMessage.getReceiverName())
                    && MessageStatus.DIDNT_READ.equals(privateMessage
                            .getStatus())) {
                System.out.println(privateMessage.getSenderName() + ": "
                        + privateMessage.getContent());

            }
            privateMessage.setStatus(MessageStatus.ALREADY_READ);
        }
    }

    if (hasNewMessages()) {
        for (PrivateChat pm : pmChat) {
            for (Message message : pm.getMessages()) {
                if (pm.getAddUserName().equals(currentUser)) {
                    System.out.println(message.getSenderName() + ": "
                            + message.getContent());
                }
            }
        }
    } else {
        System.out.println("you don't have new message ");
    }
}

private void registrationOrLogin() throws IOException {
    String logOrReg;
    System.out
            .println("Hi,if you already have account - 1,\nIf you would like to register - 2");
    logOrReg = reader.readLine();
    if (logOrReg.equals("1")) {
        login();
    } else if (logOrReg.equals("2")) {
        registration();
    } else {
        registrationOrLogin();
    }
}

private boolean hasUser() {
    boolean result = false;
    for (Registration reg : registration) {
        if (currentUser.equals(reg.getUserName())
                && password.equals(reg.getUserPassword())) {
            result = true;
        }
    }
    return result;
}

private void login() throws IOException {
    System.out.println("Please,enter user name and password ");
    currentUser = reader.readLine();
    password = reader.readLine();
    if (hasUser()) {
        System.out.println("You already logged in system");
    } else {
        System.out.println("Wrong user name or password");
        registrationOrLogin();
    }
}

private void logout() throws IOException {
    currentUser = null;
    password = null;
    registrationOrLogin();

}

private void createChat() throws IOException {
    Chat chat = new Chat();
    chat = publicChatPopulator.populate();
    publicComunication(chat);
    chats.add(chat);
}

private void joinToPrivateChat() throws IOException {
    for (PrivateChat pm : pmChat) {
        for (String user : pm.getUsers()) {
            if (user.equals(currentUser)) {
                System.out.println(pm.getChatName());
            }
        }
    }
    System.out.println("Enter the name of the chat you wish to join");
    chatName = reader.readLine();
    for (PrivateChat pm : pmChat) {

        if (chatName.equals(pm.getChatName())) {

            for (Message message : pm.getMessages()) {
                System.out.println(message.getSenderName() + " "
                        + message.getContent());
            }
            privateComunication(pm);
        }

    }

}

private void createPrivateChat() throws IOException {
    PrivateChat privateChat = new PrivateChat();
    Set<String> chatUsers = new HashSet<String>();
    privateChat = privateChatPopulator.populate();
    while (true) {
        privateChat.setAddUserName(reader.readLine());
        chatUsers.add(privateChat.getAddUserName());
        privateChat.setUsers(chatUsers);
        for (String user : users) {
            if (user.equals(privateChat.getAddUserName())) {
                System.out.println("you add too chat user - "
                        + privateChat.getAddUserName());
            }
        }
        if (privateChat.getAddUserName().equals(START_CHAT)) {
            break;
        }

    }
    privateComunication(privateChat);
    pmChat.add(privateChat);
}

private void registration() throws IOException {
    Registration reg = registrationPopulator.populate();
    registration.add(reg);
    currentUser = reg.getUserName();
    users.add(reg.getUserName());

}

private void privateComunication(PrivateChat privateChat) {
    while (true) {
        Message message = messagePopulator.populate();
        message.setSenderName(currentUser);
        System.out.println(message.getSenderName());
        System.out.println("\t" + message.getContent());

        if (EXIT.equals(message.getContent())) {
            break;
        }
        privateChat.setStatus(MessageStatus.DIDNT_READ);
        privateChat.addMessage(message);
    }
}

private void publicComunication(Chat chat) {
    while (true) {
        Message message = messagePopulator.populate();
        message.setSenderName(currentUser);
        System.out.println(message.getSenderName());
        System.out.println("\t" + message.getContent());

        if (EXIT.equals(message.getContent())) {
            break;
        }
        chat.addMessage(message);
    }
}

}