This program uses a set to print all unique words in System.in

    
/*
   This program is a part of the companion code for Core Java 8th ed.
   (http://horstmann.com/corejava)

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Set;

/**
 * This program uses a set to print all unique words in System.in.
 * @version 1.10 2003-08-02
 * @author Cay Horstmann
 */
public class SetTest
{
   public static void main(String[] args)
   {
      Set<String> words = new HashSet<String>(); // HashSet implements Set
      long totalTime = 0;

      Scanner in = new Scanner(System.in);
      while (in.hasNext())
      {
         String word = in.next();
         long callTime = System.currentTimeMillis();
         words.add(word);
         callTime = System.currentTimeMillis() - callTime;
         totalTime += callTime;
      }

      Iterator<String> iter = words.iterator();
      for (int i = 1; i <= 20 && iter.hasNext(); i++)
         System.out.println(iter.next());
      System.out.println(". . .");
      System.out.println(words.size() + " distinct words. " + totalTime + " milliseconds.");
   }
}

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This program uses a set to print all unique words in System.in : Set « Collections Data Structure « Java

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