package org.djutils.immutablecollections;
   
   import java.util.HashSet;
   
   /**
    * Demonstration code.
    * @author pknoppers
    */
   public final class ImmutableCollectionsDemo
  {
      /**
       * Do not instantiate.
       */
      private ImmutableCollectionsDemo()
      {
          // Do not instantiate
      }
  
      /**
       * Demo code.
       * @param args String[]; not used
       */
      public static void main(final String[] args)
      {
          HashSet<String> hashSet = new HashSet<>(); // Create a normal HashSet containing Strings
          hashSet.add("String 1"); // Add a String
          hashSet.add("String 2"); // Add another String
          System.out.println("normal hash set contains: " + hashSet);
          ImmutableHashSet<String> immutableHashSetWithCopy = new ImmutableHashSet<>(hashSet); // Makes a copy
          ImmutableHashSet<String> immutablehashSetThatWraps = new ImmutableHashSet<>(hashSet, Immutable.WRAP);
          System.out.println("immutable hash set with copy:  " + immutableHashSetWithCopy); // Contains two Strings
          System.out.println("immutable hash set that wraps: " + immutablehashSetThatWraps); // Contains two Strings
          hashSet.add("String 3"); // Modify the original hash set by adding a third String
          System.out.println("immutable hash set with copy:  " + immutableHashSetWithCopy); // Contains two Strings
          System.out.println("immutable hash set that wraps: " + immutablehashSetThatWraps); // Contains three Strings
          ImmutableIterator<String> immutableIterator = immutableHashSetWithCopy.iterator(); // Create an Iterator
          while (immutableIterator.hasNext()) // Iterate over the immutable hash set
          {
              String string = immutableIterator.next();
              System.out.println("string is " + string);
              immutableIterator.remove(); // Throws UnsupportedOperationException
          }
          // immutableHashSetWithCopy.add("String 4"); // does not compile; there is no add method
          // immutableHashSetThatWraps.add("String 4"); // does not compile; there is no add method
          // immutableHashSetWithCopy.remove("String 2"); // does not compile; there is no add method
          // immutableHashSetThatWraps.remove("String 2"); // does not compile; there is no add method
      }
  
  }