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/*******************************************************************************
* Copyright (c) 2007, 2008 IBM Corporation and others.
* 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:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.equinox.internal.provisional.p2.query;
import java.lang.reflect.Array;
import java.util.*;
/**
* A collector is a generic visitor that collects objects passed to it,
* and can then express the result of the visit in various forms. The collector
* can also short-circuit a traversal by returning <code>false</code> from
* its {@link #accept(Object)} method.
* <p>
* This default collector just accepts all objects passed to it. Clients may subclass
* to perform different processing on the objects passed to it.
*/
public class Collector {
private Set collected = null;
/**
* Creates a new collector.
*/
public Collector() {
super();
}
/**
* Accepts an object.
* <p>
* This default implementation adds the objects to a list. Clients may
* override this method to perform additional filtering, add different objects
* to the list, short-circuit the traversal, or process the objects directly without
* collecting them.
*
* @param object the object to collect or visit
* @return <code>true</code> if the traversal should continue,
* or <code>false</code> to indicate the traversal should stop.
*/
public boolean accept(Object object) {
getCollection().add(object);
return true;
}
/**
* Returns the collection that is being used to collect results. Unlike {@toCollection},
* this returns the actual modifiable collection that is being used to store results. The
* return value is only intended to be used within subclasses and should not be exposed
* outside of a collection class.
*
* @return the collection being used to collect results.
*/
protected Collection getCollection() {
if (collected == null)
collected = new HashSet();
return collected;
}
/**
* Returns whether this collector is empty.
* @return <code>true</code> if this collector has accepted any results,
* and <code>false</code> otherwise.
*/
public boolean isEmpty() {
return collected == null || collected.isEmpty();
}
/**
* Returns an iterator on the collected objects.
*
* @return an iterator of the collected objects.
*/
public Iterator iterator() {
return collected == null ? Collections.EMPTY_LIST.iterator() : collected.iterator();
}
/**
* Returns the number of collected objects.
*/
public int size() {
return collected == null ? 0 : collected.size();
}
/**
* Returns the collected objects as an array
*
* @param clazz The type of array to return
* @return The array of results
* @throws ArrayStoreException the runtime type of the specified array is
* not a supertype of the runtime type of every collected object
*/
public Object[] toArray(Class clazz) {
int size = collected == null ? 0 : collected.size();
Object[] result = (Object[]) Array.newInstance(clazz, size);
if (size != 0)
collected.toArray(result);
return result;
}
/**
* Returns the collected objects as an immutable collection.
*
* @return An unmodifiable collection of the collected objects
*/
public Collection toCollection() {
return collected == null ? Collections.EMPTY_SET : Collections.unmodifiableSet(collected);
}
}
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