RosettaCodeData/Task/Anonymous-recursion/Java/anonymous-recursion-1.java

public static long fib(int n)
{
  if (n < 0)
    throw new IllegalArgumentException("n can not be a negative number");
  return new Object() {
    private long fibInner(int n)
    {  return (n < 2) ? n : (fibInner(n - 1) + fibInner(n - 2));  }
  }.fibInner(n);
}