找不到变量 JOptionPane

如何解决找不到变量 JOptionPane

public class NetManager extends Thread {
public Multipart mp;
public String host,username,password;
public NetManager(String username,String password)
{
    this.host = "imap.gmail.com";
    this.username = username;
    this.password = password;
}

private Session getImapSession() {
    Properties props = new Properties();
    props.setProperty("mail.store.protocol","imap");
    props.setProperty("mail.debug","false");
    props.setProperty("mail.imap.host","imap.gmail.com");
    props.setProperty("mail.imap.port","993");
    props.setProperty("mail.imap.ssl.enable","true");
    Session session = Session.getDefaultInstance(props,null);
    session.setDebug(true);
    return session;
}
public Folder getMailBox()
{
    try
    {

        Session currentSession = getImapSession();
        Store store = currentSession.getStore("imap");
        store.connect(host,password);
        IMAPFolder inBox = (IMAPFolder)store.getFolder("INBox");
        inBox.open(Folder.READ_ONLY);
        return inBox;
    }
    catch (Exception e)
    {
        System.out.println(e.getMessage());
        return null;
    }
}
public void run() {
    super.run();
    Folder inBox = getMailBox();
    try {
        int counter = 0;
        Message[] messg = inBox.getMessages();
        for (int i = 0; i < messg.length; i++)
        {
            if(messg[i].getSubject().equals("check"))
            {
                mp = (Multipart) messg[i].getContent();
            }
        }
    } catch (MessagingException | IOException e) {
        System.out.println("Error");
    }
}

解决方法

int a=JoptionPane.show..

应该是：

int a=JOptionPane.show..

Java 区分大小写，选项窗格的第一个 'o' 是大写的 'O'。