Determine long lasting thread in JAVA

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Java

I developing a program which determine the long lasting thread. There are 5 threads with different priorities and two threads of highest priorities are kept to sleep.Also isAlive() method is used to check whether the thread is alive or not and based on that the long lasting thread is determined,but it runs in infinite loop instead of giving long lasting thread...! below is the code
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import java.util.*;
class ThreadDemo extends Thread
{
    Thread t;
    String name;
    int priority;

    ThreadDemo(int priority,String name)
    {
        this.name=name;
        this.priority=priority;
        t=new Thread(this,name);
        System.out.println("New Thread "+t);
        t.start();
    }
    public void run()
    {
            int p=t.getPriority();
            try
            {
                if(p==9 || p==8)
                {
                    t.sleep(2000);
                }
                else
                {
                    System.out.println(t.currentThread()+"is alive?"+t.isAlive());
                }
                while(t.isAlive())
                {
                    System.out.println("Long lasting thread:"+t.getName());
                }

            }
            catch(InterruptedException ie)
            {
                System.out.println("Thread Interrupted...!");
            }

    }
}
class MainThread
{
    public static void main(String args[])
    {
        //ThreadDemo a,b,c,d,e;
        new ThreadDemo(5,"One");
        new ThreadDemo(6,"Two");
        new ThreadDemo(7,"Three");
        new ThreadDemo(8,"Four");
        new ThreadDemo(9,"Five");

    }
}