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package bjc.utils.funcutils;
import java.util.*;
import java.util.function.*;
import bjc.data.ArrayIterator;
/**
* Utility methods for dealing with iterators.
*
* @author bjculkin
*
*/
public class IteratorUtils {
/**
* A chain iterator. This is essentially flatMap in iterator form.
* @author bjculkin
*
* @param <T1>
* The type of the input values.
*
* @param <T2>
* The type of the output values.
*/
public static class ChainIterator<T1, T2> implements Iterator<T2> {
private Iterator<T1> mainItr;
private Function<T1, Iterator<T2>> trans;
private Iterator<T2> curItr;
/**
* Create a new chain iterator.
*
* @param mainItr
* The main iterator for input.
*
* @param trans
* The transformation to use to produce the outputs.
*/
public ChainIterator(Iterator<T1> mainItr, Function<T1, Iterator<T2>> trans) {
this.mainItr = mainItr;
this.trans = trans;
}
@Override
public boolean hasNext() {
if (curItr != null) {
if (curItr.hasNext()) return true;
else return mainItr.hasNext();
}
return mainItr.hasNext();
}
@Override
public T2 next() {
if (curItr == null || !curItr.hasNext()) {
curItr = trans.apply(mainItr.next());
}
return curItr.next();
}
}
/**
* Convert an iterator to an iterable.
*
* @param itr
* The iterator to convert.
*
* @return An iterable that gives back that iterator.
*/
public static <E> Iterable<E> I(Iterator<E> itr) {
return () -> itr;
}
/**
* Convert an iterable to an iterator.
*
* @param itr
* The iterable to convert.
*
* @return The iterator from that iterable
*/
public static <E> Iterator<E> I(Iterable<E> itr) {
return itr.iterator();
}
/**
* Convert an array to an iterator.
*
* @param parms
* The array to iterate over.
*
* @return An iterator over the provided array.
*/
@SafeVarargs
public static <E> Iterator<E> AI(E... parms) {
return new ArrayIterator<>(parms);
}
/**
* Create a chain iterator.
*
* @param itrA
* The iterator for input values.
*
* @param itrB
* The transformation for output values.
*
* @return A chain iterator from the provided values.
*/
public static <A, B> Iterator<B> chain(Iterator<A> itrA, Function<A, Iterator<B>> itrB) {
return new ChainIterator<>(itrA, itrB);
}
}
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