Inner Class in Java: Unexpected Volatility

You probably know that if you use a value in an inner class, the evil Java compiler wants you to write "final"; people do all kinds of trick to bypass it - store date in arrays, for instance.

But relax, you do not have to write "final" if it is a member field. Look at this code:

package experimental;

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

public class VolatileConstant {

  public static void main(String[] args) {
    Iterable<Set<String>> iss = new Iterable<Set<String>>() {

      public Iterator<Set<String>> iterator() {
        return new Iterator<Set<String>>() {
          int i = 0;
          public boolean hasNext() {
            return i < 3;
          }

          public Set<String> next() {
            i++;

            return new AbstractSet<String>() {
              public Iterator<String> iterator() {
                return new Iterator<String>() {
                  int j = 0;
                  public boolean hasNext() {
                    return j < i;
                  }

                  public String next() {
                    j++;
                    return "" + i + "." + j;
                  }

                  public void remove() {
                    throw new UnsupportedOperationException();
                  }
                };
              }

              public int size() {
                return i;
              }
            };
          }

          public void remove() {
            throw new UnsupportedOperationException();
          }
        };
      }
    };

    Set<Set<String>> sss = new HashSet<Set<String>>();

    for (Set<String> ss : iss) {
      sss.add(ss);
      System.out.println(ss);
    }
    System.out.println(sss);
  }
}

You know what it prints? It's in the next line, in white color so that you have a choice not to see it.

[1.1]
[2.1, 2.2]
[3.1, 3.2, 3.3]
[[3.1, 3.2, 3.3], [3.1, 3.2, 3.3], [3.1, 3.2, 3.3]]


I am sure you can explain it, after a while, but is not it really amusing?