libcore.util.CollectionUtils Maven / Gradle / Ivy
/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package libcore.util;
import java.lang.ref.Reference;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
public final class CollectionUtils {
private CollectionUtils() {}
/**
* Returns an iterator over the values referenced by the elements of {@code
* iterable}.
*
* @param trim true to remove reference objects from the iterable after
* their referenced values have been cleared.
*/
public static Iterable dereferenceIterable(
final Iterable> iterable, final boolean trim) {
return new Iterable() {
public Iterator iterator() {
return new Iterator() {
private final Iterator> delegate = iterable.iterator();
private boolean removeIsOkay;
private T next;
private void computeNext() {
removeIsOkay = false;
while (next == null && delegate.hasNext()) {
next = delegate.next().get();
if (trim && next == null) {
delegate.remove();
}
}
}
@Override public boolean hasNext() {
computeNext();
return next != null;
}
@Override public T next() {
if (!hasNext()) {
throw new IllegalStateException();
}
T result = next;
removeIsOkay = true;
next = null;
return result;
}
public void remove() {
if (!removeIsOkay) {
throw new IllegalStateException();
}
delegate.remove();
}
};
}
};
}
/**
* Sorts and removes duplicate elements from {@code list}. This method does
* not use {@link Object#equals}: only the comparator defines equality.
*/
public static void removeDuplicates(List list, Comparator comparator) {
Collections.sort(list, comparator);
int j = 1;
for (int i = 1; i < list.size(); i++) {
if (comparator.compare(list.get(j - 1), list.get(i)) != 0) {
T object = list.get(i);
list.set(j++, object);
}
}
if (j < list.size()) {
list.subList(j, list.size()).clear();
}
}
}