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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/*******************************************************************************
 * Copyright (c) 2008, 2021 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.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

/**
 * 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();
	}
}