peekFirst

peekFirst is a method of the Deque interface in Java that retrieves, without removing, the element at the front of the deque. It returns the first element or null if the deque is empty, and it does not modify the deque’s contents. This method supports double-ended queue semantics by allowing inspection of the head without dequeuing it.

A key point is how nulls are handled. In implementations that disallow null elements (such as ArrayDeque), a null return value indicates that the deque is empty. In implementations that permit nulls (such as LinkedList), a null return could in principle reflect a real element that is null, so users should rely on the empty-check semantics or use other methods if nulls are possible.

Related methods include peekLast, which retrieves the last element without removing it, and getFirst, which also returns the first element but throws NoSuchElementException if the deque is empty. Other removal and inspection methods include pollFirst, removeFirst, and pollLast, each with its own behavior on emptiness.

Common implementations of Deque that provide peekFirst include ArrayDeque and LinkedList. ArrayDeque is often preferred for non-null elements due to its performance characteristics, while LinkedList can store null elements but may complicate null-based checks. peekFirst is frequently used when a program needs to decide whether to process or defer the head element without altering the queue structure.