org.eclipse.osgi.internal.serviceregistry.ShrinkableCollection Maven / Gradle / Ivy
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/*******************************************************************************
* Copyright (c) 2008, 2016 IBM Corporation and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.osgi.internal.serviceregistry;
import java.util.*;
/**
* A Shrinkable Collection. This class provides a wrapper for a list of collections
* that allows items to be removed from the wrapped collections (shrinking) but
* does not allow items to be added to the wrapped collections.
*
*
* The collections must act as sets in that each collection in the list
* must not have two entries which are equal.
*
*
* All the optional Collection operations except
* add and addAll are supported. Attempting to add to the
* collection will result in an UnsupportedOperationException.
*
*/
public class ShrinkableCollection implements Collection {
private final Collection collection;
private final List> list;
public ShrinkableCollection(Collection c) {
if (c == null) {
throw new NullPointerException();
}
List> empty = Collections.> emptyList();
list = empty;
collection = c;
}
public ShrinkableCollection(Collection c1, Collection c2) {
list = new ArrayList<>(2);
list.add(c1);
list.add(c2);
collection = initComposite(list);
}
public ShrinkableCollection(List> l) {
list = new ArrayList<>(l);
collection = initComposite(list);
}
private static Collection initComposite(List> collections) {
int size = 0;
for (Collection c : collections) {
assert verifyNoDuplicates(c);
size += c.size();
}
Collection result = new ArrayList<>(size);
for (Collection c : collections) {
for (E e : c) {
if (!result.contains(e)) {
result.add(e);
}
}
}
return result;
}
private static boolean verifyNoDuplicates(Collection c) {
for (E e : c) {
int count = 0;
for (E f : c) {
if (e == null) {
if (f == null) {
count++;
}
} else {
if (e.equals(f)) {
count++;
}
}
}
if (count != 1) {
return false;
}
}
return true;
}
@Override
public boolean add(E e) {
throw new UnsupportedOperationException();
}
@Override
public boolean addAll(Collection c) {
throw new UnsupportedOperationException();
}
@Override
public void clear() {
collection.clear();
for (Collection c : list) {
c.clear();
}
}
@Override
public boolean contains(Object o) {
return collection.contains(o);
}
@Override
public boolean containsAll(Collection c) {
return collection.containsAll(c);
}
@Override
public boolean isEmpty() {
return collection.isEmpty();
}
@Override
public Iterator iterator() {
@SuppressWarnings("unchecked")
final Iterator iter = (Iterator) collection.iterator();
final List> collections = list;
if (collections.isEmpty()) {
return iter;
}
return new Iterator() {
private E last;
@Override
public boolean hasNext() {
return iter.hasNext();
}
@Override
public E next() {
last = iter.next();
return last;
}
@Override
public void remove() {
iter.remove();
for (Collection c : collections) {
c.remove(last);
}
}
};
}
@Override
public boolean remove(Object o) {
final boolean result = collection.remove(o);
if (result) {
for (Collection c : list) {
c.remove(o);
}
}
return result;
}
@Override
public boolean removeAll(Collection c) {
final boolean result = collection.removeAll(c);
if (result) {
for (Collection cc : list) {
cc.removeAll(c);
}
}
return result;
}
@Override
public boolean retainAll(Collection c) {
final boolean result = collection.retainAll(c);
if (result) {
for (Collection cc : list) {
cc.retainAll(c);
}
}
return result;
}
@Override
public int size() {
return collection.size();
}
@Override
public Object[] toArray() {
return collection.toArray();
}
@Override
public T[] toArray(T[] var0) {
return collection.toArray(var0);
}
@Override
public String toString() {
return collection.toString();
}
}