- All Implemented Interfaces:
Iterator<T>
Iterator
interface, to make this
interface easier to implement for certain types of data sources.
Iterator
requires its implementations to support querying the end-of-data status
without changing the iterator's state, using the hasNext()
method. But many data sources,
such as Reader.read()
, do not expose this information; the only way to discover
whether there is any data left is by trying to retrieve it. These types of data sources are
ordinarily difficult to write iterators for. But using this class, one must implement only the
computeNext()
method, and invoke the endOfData()
method when appropriate.
Another example is an iterator that skips over null elements in a backing iterator. This could be implemented as:
public static Iterator<String> skipNulls(final Iterator<String> in) {
return new AbstractIterator<String>() {
protected String computeNext() {
while (in.hasNext()) {
String s = in.next();
if (s != null) {
return s;
}
}
return endOfData();
}
};
}
This class supports iterators that include null elements.
- Since:
- 2.0
- Author:
- Kevin Bourrillion
-
Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionReturns the next element.Implementations ofcomputeNext()
must invoke this method when there are no elements left in the iteration.final boolean
hasNext()
final T
next()
final T
peek()
Returns the next element in the iteration without advancing the iteration, according to the contract ofPeekingIterator.peek()
.Methods inherited from class com.google.common.collect.UnmodifiableIterator
remove
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
-
Constructor Details
-
AbstractIterator
protected AbstractIterator()Constructor for use by subclasses.
-
-
Method Details
-
computeNext
Returns the next element. Note: the implementation must callendOfData()
when there are no elements left in the iteration. Failure to do so could result in an infinite loop.The initial invocation of
hasNext()
ornext()
calls this method, as does the first invocation ofhasNext
ornext
following each successful call tonext
. Once the implementation either invokesendOfData
or throws an exception,computeNext
is guaranteed to never be called again.If this method throws an exception, it will propagate outward to the
hasNext
ornext
invocation that invoked this method. Any further attempts to use the iterator will result in anIllegalStateException
.The implementation of this method may not invoke the
hasNext
,next
, orpeek()
methods on this instance; if it does, anIllegalStateException
will result.- Returns:
- the next element if there was one. If
endOfData
was called during execution, the return value will be ignored. - Throws:
RuntimeException
- if any unrecoverable error happens. This exception will propagate outward to thehasNext()
,next()
, orpeek()
invocation that invoked this method. Any further attempts to use the iterator will result in anIllegalStateException
.
-
endOfData
Implementations ofcomputeNext()
must invoke this method when there are no elements left in the iteration.- Returns:
null
; a convenience so yourcomputeNext
implementation can use the simple statementreturn endOfData();
-
hasNext
-
next
-
peek
Returns the next element in the iteration without advancing the iteration, according to the contract ofPeekingIterator.peek()
.Implementations of
AbstractIterator
that wish to expose this functionality should implementPeekingIterator
.
-