Method getOnlyElement

corpus/java/training/guava/collect/Iterators.java:308–326

Returns the single element contained in iterator. @throws NoSuchElementException if the iterator is empty @throws IllegalArgumentException if the iterator contains multiple elements. The state of the iterator is unspecified.

(Iterator<T> iterator)

   *     elements.  The state of the iterator is unspecified.
   */
  @CanIgnoreReturnValue // TODO(kak): Consider removing this?
  public static <T> T getOnlyElement(Iterator<T> iterator) {
    T first = iterator.next();
    if (!iterator.hasNext()) {
      return first;
    }

    StringBuilder sb = new StringBuilder();
    sb.append("expected one element but was: <" + first);
    for (int i = 0; i < 4 && iterator.hasNext(); i++) {
      sb.append(", " + iterator.next());
    }
    if (iterator.hasNext()) {
      sb.append(", ...");
    }
    sb.append('>');

    throw new IllegalArgumentException(sb.toString());
  }

  /**
   * Returns the single element contained in {@code iterator}, or {@code