CanonicalSet.java

/*******************************************************************************
 * Copyright (c) 2012 Michael Kutschke.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     Michael Kutschke - initial API and implementation
 ******************************************************************************/
package org.eclipse.recommenders.jayes.util.sharing;

import java.util.AbstractSet;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/**
 * Set to support managing canonical, shared instances. These instances should be immutable while in the set. Call
 * get(T) to get a canonical instance for the specified key.
 *
 * @param <T>
 */
public abstract class CanonicalSet<T> extends AbstractSet<T> {

    private final Map<Entry<T>, T> set = new HashMap<>();

    public T get(final T example) {
        final Entry<T> entry = createEntry(example);
        final T inst = set.get(entry);
        if (entry.equals(createEntry(inst))) {
            return inst;
        }
        // Entry has changed - remove it
        set.remove(entry);
        return null;
    }

    protected abstract Entry<T> createEntry(T array);

    @Override
    public boolean add(final T e) {
        if (!contains(e)) {
            return set.put(createEntry(e), e) == null;
        } else {
            return false;
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public boolean contains(final Object o) {
        return hasProperType(o) ? set.containsKey(createEntry((T) o)) : false;
    }

    /**
     * @return true iff o is of type T
     */
    protected abstract boolean hasProperType(Object o);

    @Override
    public Iterator<T> iterator() {
        return set.values().iterator();
    }

    @SuppressWarnings("unchecked")
    @Override
    public boolean remove(final Object o) {
        if (!hasProperType(o)) {
            return false;
        }
        return set.remove(createEntry((T) o)) != null;
    }

    @Override
    public boolean retainAll(final Collection<?> c) {
        throw new UnsupportedOperationException("Unimplemented");
    }

    @Override
    public int size() {
        return set.size();
    }
}