Performance penalty of String.intern()

Question

Lots of people talk about the performance advantages of String.intern(), but I\'m actually more interested in what the performance penalty may be.

My main concerns a

Answer 1

The following micro benchmark suggests using an enum offers around a ten times performance improvement (the usual micro benchmark caveats apply) test code as follows:

public class Test {
   private enum E {
      E1;
      private static final Map named = new HashMap();
      static {
         for (E e : E.values()) {
            named.put( e.name(), e );
         }
      }

      private static E get(String s) {
         return named.get( s );
      }
   }

   public static void main(String... strings) {
      E e = E.get( "E1" ); // ensure map is initialised

      long start = System.nanoTime();
      testMap( 10000000 );
      long end = System.nanoTime();

      System.out.println( 1E-9 * (end - start) );
   }

   private static void testIntern(int num) {
      for (int i = 0; i < num; i++) {
         String s = "E1".intern();
      }
   }

   private static void testMap(int num) {
      for (int i = 0; i < num; i++) {
         E e = E.get( "E1" );
      }
   }
}

Results (10 million iterations): testIntern() - 0.8 seconds testMap() - 0.06 seconds

Of course YMMV, but enums offer so many benefits over Strings...type-safety over other random Strings, ability to add methods etc. seems the best way to go imho