Class LazyIteratorChain<E>
- All Implemented Interfaces:
Iterator<E>
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
-
Field Summary
FieldsModifier and TypeFieldDescriptionprivate int
The number of timesnext()
was already called.private boolean
Indicates that the Iterator chain has been exhausted.The current iterator.The "last used" Iterator is the Iterator upon which next() or hasNext() was most recently called used for the remove() operation only. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionboolean
hasNext()
Return true if any Iterator in the chain has a remaining element.next()
Returns the next element of the current IteratornextIterator
(int count) Gets the next iterator after the previous one has been exhausted.void
remove()
Removes from the underlying collection the last element returned by the Iterator.private void
Updates the current iterator field to ensure that the current Iterator is not exhausted.Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods inherited from interface java.util.Iterator
forEachRemaining
-
Field Details
-
callCounter
private int callCounterThe number of timesnext()
was already called. -
chainExhausted
private boolean chainExhaustedIndicates that the Iterator chain has been exhausted. -
currentIterator
The current iterator. -
lastUsedIterator
The "last used" Iterator is the Iterator upon which next() or hasNext() was most recently called used for the remove() operation only.
-
-
Constructor Details
-
LazyIteratorChain
public LazyIteratorChain()
-
-
Method Details
-
nextIterator
Gets the next iterator after the previous one has been exhausted.This method MUST return null when there are no more iterators.
- Parameters:
count
- the number of time this method has been called (starts with 1)- Returns:
- the next iterator, or null if there are no more.
-
updateCurrentIterator
private void updateCurrentIterator()Updates the current iterator field to ensure that the current Iterator is not exhausted. -
hasNext
public boolean hasNext()Return true if any Iterator in the chain has a remaining element. -
next
Returns the next element of the current Iterator- Specified by:
next
in interfaceIterator<E>
- Returns:
- element from the current Iterator
- Throws:
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 interfaceIterator<E>
- Throws:
UnsupportedOperationException
- if the remove operator is not supported by the underlying IteratorIllegalStateException
- 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.
-