LINQ's Single in java?

Question

Is there an equivalent to LINQ's Single in java? Perhaps in lambdaj?

Answer 1

Using Guava:

Iterables.getOnlyElement(Iterable< T > iterable)

Answer 2

It's a pretty easy one to implement yourself, to be honest:

public static <T> T single(Iterable<T> source) {
  Iterator<T> iterator = source.iterator();
  if (!iterator.hasNext()) {
    throw new IllegalArgumentException("No elements");
  }
  T first = iterator.next();
  if (iterator.hasNext()) {
    throw new IllegalArgumentException("More than one element");
  }
  return first;
}

(Or put it in a generic class instead of making the method generic. You may decide to use a different exception type, too.)

Answer 3

A less defensive version of @Jon's solution.

Collection<T> coll;
T first = col.iterator().next();

Add checks to taste.

Answer 4

If you can use my xpresso library you can write: x.list(iterable).toScalar();