Package org.apache.commons.collections4.iterators

Class LazyIteratorChain<E>

  • All Implemented Interfaces:
    java.util.Iterator<E>
    public abstract class LazyIteratorChain<E>
extends java.lang.Object
implements java.util.Iterator<E>
    An LazyIteratorChain is an Iterator that wraps a number of Iterators in a lazy manner.

    This class makes multiple iterators look like one to the caller. When any method from the Iterator interface is called, the LazyIteratorChain will delegate to a single underlying Iterator. The LazyIteratorChain will invoke the Iterators in sequence until all Iterators are exhausted.

    The Iterators are provided by nextIterator(int) which has to be overridden by sub-classes and allows to lazily create the Iterators as they are accessed: 

     return new LazyIteratorChain<String>() {
     protected Iterator<String> nextIterator(int count) {
         return count == 1 ? Arrays.asList("foo", "bar").iterator() : null;
     }
 };

    Once the inner Iterator's Iterator.hasNext() method returns false, nextIterator(int) will be called to obtain another iterator, and so on until nextIterator(int) returns null, indicating that the chain is exhausted.

    NOTE: The LazyIteratorChain may contain no iterators. In this case the class will function as an empty iterator.

    Since:
    4.0

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean hasNext()
      Return true if any Iterator in the chain has a remaining element.
      E next()
      Returns the next element of the current Iterator
      void remove()
      Removes from the underlying collection the last element returned by the Iterator.

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

      • Methods inherited from interface java.util.Iterator

        forEachRemaining

    • Constructor Detail

      • LazyIteratorChain

        public LazyIteratorChain()

    • Method Detail

      • hasNext

        public boolean hasNext()
        Return true if any Iterator in the chain has a remaining element.
        Specified by:
        hasNext in interface java.util.Iterator<E>
        Returns:
        true if elements remain

      • next

        public E next()
        Returns the next element of the current Iterator
        Specified by:
        next in interface java.util.Iterator<E>
        Returns:
        element from the current Iterator
        Throws:
        java.util.NoSuchElementException - if all the Iterators are exhausted

      • remove

        public void remove()
        Removes from the underlying collection the last element returned by the Iterator.

        As with next() and hasNext(), this method calls remove() on the underlying Iterator. Therefore, this method may throw an UnsupportedOperationException if the underlying Iterator does not support this method.

        Specified by:
        remove in interface java.util.Iterator<E>
        Throws:
        java.lang.UnsupportedOperationException - if the remove operator is not supported by the underlying Iterator
        java.lang.IllegalStateException - if the next method has not yet been called, or the remove method has already been called after the last call to the next method.