When thread is destroyed Java

I have following codes. In the main method, I start two threads. How could I detect when thread finnish its mission/is destroyed?

public class CounterThread extends Thread {
	
	public CounterThread(String name){
		super(name);
	}

	public void run(){
		int limit=0;
		while(limit<250){
			limit++;
			try{
			  Thread.sleep(30);
			}catch(InterruptedException ie){
				ie.printStackTrace();
			}
		    synchronized(Counter.getInstance()){	
			   increaseCounter();
			   print(Counter.getInstance());
		    }   		
		}
	}
	
	public void increaseCounter(){
		Counter.getInstance().increaseCounter();
	}
	
    public void print(Counter counter){
    	System.out.println("Thread "+getName()+" is running :Counter now is: "+counter.getCounter());
    	
    }
    
  
    public static void main(String[] args){
        CounterThread ct1 = new CounterThread("ct1");
        CounterThread ct2 = new CounterThread("ct2");
         
        ct1.start();
        ct2.start();
 
    }
}