ThreadClass.java

public class ThreadClass extends Thread {
    private Thread thread;
    private Vector<Mails> mailQueue = new Vector<Mails>();

    public void start(Vector<Mails> mailQueue) {
        if (thread == null) {
            this.mailQueue = mailQueue;
            thread = new Thread(this);
            thread.start();
        }
    }

    public void run() {
        //Update share resource
        synchronized (this) {
            updateNoteBook();
        }
        // Other operation here
    }

    public static synchronized updateNoteBook() {
        // Do whatever necessary
        // The function can be called by one thread at the same time
    }
}