Creates an EnumSet with a couple elements and prints it in String and OutputStream format.

EnumSetFormat.java

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.EnumSet;

class Scratch {
  enum Fruit {APPLE, ORANGE};
  public static void main(String[] args) throws IOException {
    final EnumSet<Fruit> fruits = EnumSet.of(Fruit.APPLE, Fruit.ORANGE);
    final String serialized = serializeToString(fruits);
    System.out.println(String.format("fruits as String:%n%s%n…as OutputStream (length %d chars):%n%s",
        fruits, serialized.length(), serialized));
  }
  private static String serializeToString(final Serializable s) throws IOException {
    try (final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
         final ObjectOutputStream    oos = new ObjectOutputStream(buffer)) {
      oos.writeObject(s);
      return buffer.toString();
    }
  }
}

outputs:

fruits as String:
[APPLE, ORANGE]
…as OutputStream (length 248 chars):
Scratch$Fruit�����������xr��java.lang.Enum�����������xpur��[Ljava.lang.Enum;���-3�/����xp����~q�~��t��APPLE~q�~��t��ORANGE