What loop termination condition of this program is ?

If the title is basically a program book, has been in the black window, input state , input what end?

import java.util.*;
  
  public class Test
  {
  		public static void main(String[] args)
  		{
  		     Set<String> words = new HashSet<String>();				
  		     long totalTime = 0;
  				
  		      Scanner in = new Scanner(System.in);
  		      while(in.hasNext())              //这个循环的终止条件是什么       
                                                       //呀，怎么在黑窗口中一直是输入状态？输入一 
                                                        //个什么会终止？
  		      {
  			  String s = in.next();
  			  long callTime = System.currentTimeMills();
  			  words.add(s);	
  			  callTime = System.currentTimeMills() - callTime;
  			  totalTime = totalTime + callTime;
  		      }
  				
  		     Iterator<String> it = words.iterator();
  		     for(int i=1; i<=20 && it.hasNext(); i++)
  		     {
  			 System.out.println(it.next());	
  		     }
  				
  		}	
  }
  
  

------ Solution ------------------------------------- -------
this cycle does not terminate , should you end up manually input stream on the line .. looks like Ctrl + z. Try
------ Solution -------------------------------------- ------

  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.Scanner;
  import java.util.Set;
  
  public class Test {
  	public static void main(String[] args) {
  		Set<String> words = new HashSet<String>();
  		long totalTime = 0;
  
  		Scanner in = new Scanner(System.in);
  		while (in.hasNext()) // 这个循环的终止条件是什么
  								// 呀，怎么在黑窗口中一直是输入状态？输入一
  								// 个什么会终止？
  		{
  			String s = in.next();
  			long callTime = System.currentTimeMillis();
  			words.add(s);
  			callTime = System.currentTimeMillis() - callTime;
  			totalTime = totalTime + callTime;
  			if(s.equals("exit")){ // 加个判断条件
  				break;
  			}
  		}
  
  		Iterator<String> it = words.iterator();
  		for (int i = 1; i <= 20 && it.hasNext(); i++) {
  			System.out.println(it.next());
  		}
  
  	}
  }
  
  

------ Solution ---------------------------- ----------------
own prices termination conditions such as when you knock into the character equals ** This is on break out of the loop .
------ For reference only -------------------------------------- -
Thank you , indeed either manually ctrl + z, or add a judgment conditions . Meanwhile my original program has a word wrong currentTimeMills, in front of one less s i. Causing me good looking.