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/*
* esodata - data structures and other things, of varying utility
* Copyright 2022, Ben Culkin
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
package bjc.data;
import java.util.*;
/*
* @TODO Oct 6, 2020 - Ben Culkin - :CleverCache
*
* In the future, there are certain efficiencies we could take with our cached
* elements; namely, the case where we repeat the same element multiple times,
* or the case where we have a mixture of identical (and probably sizable) elements
*
* The general downside to these of course, is that these efficiencies would cost
* us something in terms of complexity, as well as not benefiting iterators which
* aren't large enough.
*
* Still an interesting thought as to the best way to implement such a thing though.
*/
/**
* An iterator which can go back to the beginning of its iteration sequence at
* any point.
*
* @author Ben Culkin
*
* @param <T>
* The type iterated over.
*/
public class ResettableIterator<T> implements Iterator<T> {
private List<T> cache;
private Iterator<T> backing;
private boolean isRepeating = false;
private Iterator<T> cacheIterator;
/**
* Create a new resettable iterator.
*
* @param itr
* The iterator to iterate over.
*/
public ResettableIterator(Iterator<T> itr) {
backing = itr;
cache = new ArrayList<>();
}
/**
* Create a new resettable iterator.
*
* @param itr
* The iterable to iterate over.
*/
public ResettableIterator(Iterable<T> itr) {
this(itr.iterator());
}
@Override
public boolean hasNext() {
if (isRepeating) return cacheIterator.hasNext() ? true : backing.hasNext();
return backing.hasNext();
}
@Override
public T next() {
if (isRepeating) {
if (cacheIterator.hasNext()) {
return cacheIterator.next();
}
cacheIterator = null;
isRepeating = false;
}
T itm = backing.next();
cache.add(itm);
return itm;
}
/**
* Reset this iterator to its starting point.
*/
public void reset() {
isRepeating = true;
cacheIterator = cache.iterator();
}
/**
* Clears the cache of items.
*
* This will immediately return the iterator to the last actual item from the
* sequence, as well as making that the first item to be iterated over in the
* future.
*/
public void clearCache() {
isRepeating = false;
cacheIterator = null;
cache = new ArrayList<>();
}
}
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