// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.tools;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.Predicate;
/**
* Filtered view of a collection.
* (read-only collection, but elements can be changed, of course)
* Lets you iterate through those elements of a given collection that satisfy a
* certain condition (imposed by a predicate).
* <p>
* The behaviour of this class is undefined if the underlying collection is changed.
* @param <S> element type of the underlying collection
* @param <T> element type of filtered collection (and subclass of S). The predicate
* must accept only objects of type T.
* @since 3147
*/
public class SubclassFilteredCollection<S, T extends S> extends AbstractCollection<T> {
private final Collection<? extends S> collection;
private final Predicate<? super S> predicate;
private int size = -1;
private class FilterIterator implements Iterator<T> {
private final Iterator<? extends S> iterator;
private S current;
FilterIterator(Iterator<? extends S> iterator) {
this.iterator = iterator;
}
private void findNext() {
if (current == null) {
while (iterator.hasNext()) {
current = iterator.next();
if (predicate.test(current))
return;
}
current = null;
}
}
@Override
public boolean hasNext() {
findNext();
return current != null;
}
@SuppressWarnings("unchecked")
@Override
public T next() {
if (!hasNext())
throw new NoSuchElementException();
S old = current;
current = null;
// we are save because predicate only accepts objects of type T
return (T) old;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
/**
* Constructs a new {@code SubclassFilteredCollection}.
* @param collection The base collection to filter
* @param predicate The predicate to use as filter
* @see #filter(Collection, Predicate) for an alternative way to construct this.
*/
public SubclassFilteredCollection(Collection<? extends S> collection, Predicate<? super S> predicate) {
this.collection = collection;
this.predicate = predicate;
}
@Override
public Iterator<T> iterator() {
return new FilterIterator(collection.iterator());
}
@Override
public int size() {
if (size == -1) {
size = 0;
Iterator<T> it = iterator();
while (it.hasNext()) {
size++;
it.next();
}
}
return size;
}
@Override
public boolean isEmpty() {
return !iterator().hasNext();
}
/**
* Create a new filtered collection without any constraints on the predicate type.
* @param <T> The collection type.
* @param collection The collection to filter.
* @param predicate The predicate to filter for.
* @return The filtered collection. It is a {@code Collection<T>}.
*/
public static <T> SubclassFilteredCollection<T, T> filter(Collection<? extends T> collection, Predicate<T> predicate) {
return new SubclassFilteredCollection<>(collection, predicate);
}
}