iteratorhasNext

Iterator hasNext is a method commonly found in iterator interfaces that reports whether more elements remain to be traversed. It is a predicate and generally does not advance the iteration; it answers the question of whether a next element exists.

In Java, the typical example is the java.util.Iterator interface, which defines hasNext() and next(). The common usage pattern is while (it.hasNext()) { Object o = it.next(); }. hasNext may reflect the current state of the underlying collection, and some implementations can throw a concurrent modification exception if the collection is altered during iteration. Conventions vary, but hasNext is expected to be safe to call multiple times before a subsequent next().

Semantics and guarantees vary by language and implementation. If hasNext() returns true, a call to next() should yield the next element, and if hasNext() returns false, calling next() should throw a NoSuchElementException (in languages with that contract). Some iterators may prefetch or look ahead to determine availability, which can affect performance characteristics.

Other languages use different names or constructs for a similar concept. For example, Python iterations rely on StopIteration raised by the iterator, rather than a hasNext-like check, while C# uses MoveNext() on IEnumerator, which advances the sequence and returns whether a next element exists. The exact contract of hasNext and its alternatives depends on the language and library in use.