Class PushbackIterator<E>

java.lang.Object
org.apache.commons.collections4.iterators.PushbackIterator<E>
All Implemented Interfaces:
Iterator<E>

public class PushbackIterator<E> extends Object implements Iterator<E>
Decorates an iterator to support pushback of elements.

The decorator stores the pushed back elements in a LIFO manner: the last element that has been pushed back, will be returned as the next element in a call to next().

The decorator does not support the removal operation. Any call to remove() will result in an UnsupportedOperationException.

Since:
4.0
  • Field Details

    • iterator

      private final Iterator<? extends E> iterator
      The iterator being decorated.
    • items

      private final Deque<E> items
      The LIFO queue containing the pushed back items.
  • Constructor Details

    • PushbackIterator

      public PushbackIterator(Iterator<? extends E> iterator)
      Constructor.
      Parameters:
      iterator - the iterator to decorate
  • Method Details

    • pushbackIterator

      public static <E> PushbackIterator<E> pushbackIterator(Iterator<? extends E> iterator)
      Decorates the specified iterator to support one-element lookahead.

      If the iterator is already a PushbackIterator it is returned directly.

      Type Parameters:
      E - the element type
      Parameters:
      iterator - the iterator to decorate
      Returns:
      a new peeking iterator
      Throws:
      NullPointerException - if the iterator is null
    • pushback

      public void pushback(E item)
      Push back the given element to the iterator.

      Calling next() immediately afterwards will return exactly this element.

      Parameters:
      item - the element to push back to the iterator
    • hasNext

      public boolean hasNext()
      Specified by:
      hasNext in interface Iterator<E>
    • next

      public E next()
      Specified by:
      next in interface Iterator<E>
    • remove

      public void remove()
      This iterator will always throw an UnsupportedOperationException.
      Specified by:
      remove in interface Iterator<E>
      Throws:
      UnsupportedOperationException - always