我想用这个代码通过javamail api发送附件。
我找到了这个类的代码，但是我不知道如何从mainactivity调用它。我是android studio的新开发人员。我已经在mainfest.xml中授予了权限。请让我知道我做错了什么，需要实现什么。非常感谢任何帮助。无法将文件作为电子邮件附件附加。
sendmail.class类

import java.io.IOException;
import java.util.Properties;

import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;

public class SendEmail {

    public static void main(String[] args) {
        //authentication info
        final String username = "........@gmail.com";
        final String password = "........";
        String fromEmail = "........@gmail.com";
        String toEmail = "......gmail.com";

        Properties properties = new Properties();
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable", "true");
        properties.put("mail.smtp.host", "smtp.gmail.com");
        properties.put("mail.smtp.port", "587");

        Session session = Session.getInstance(properties, new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username,password);
            }
        });
        //Start our mail message
        MimeMessage msg = new MimeMessage(session);
        try {
            msg.setFrom(new InternetAddress(fromEmail));
            msg.addRecipient(Message.RecipientType.TO, new InternetAddress(toEmail));
            msg.setSubject("Subject Line");

            Multipart emailContent = new MimeMultipart();

            //Text body part
            MimeBodyPart textBodyPart = new MimeBodyPart();
            textBodyPart.setText("My multipart text");

            //Attachment body part.
            MimeBodyPart pdfAttachment = new MimeBodyPart();
            pdfAttachment.attachFile("/home/parallels/Documents/docs/javamail.pdf");

            //Attach body parts
            emailContent.addBodyPart(textBodyPart);
            emailContent.addBodyPart(pdfAttachment);

            //Attach multipart to message
            msg.setContent(emailContent);

            Transport.send(msg);
            System.out.println("Sent message");
        } catch (MessagingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

}

主要活动；

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

//there must be a code here

    }
}