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/*******************************************************************************
* Copyright (c) 2009 EclipseSource 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:
* EclipseSource - initial API and implementation
* IBM Corporation - ongoing development
******************************************************************************/
package org.eclipse.equinox.p2.query;
import java.util.Iterator;
import org.eclipse.equinox.p2.metadata.expression.IExpression;
/**
* This class represents the superclass of most of p2's queries. Every element
* in the query can be evaluated by calling isMatch on it. If {@link #isMatch(Object)} returns true,
* then the element WILL be included in the query result. If {@link #isMatch(Object)} returns false, then
* the element WILL NOT be included in the query result.
* <p>
* This class may be subclassed by clients. Subclasses should specify the type
* of object they support querying on. Subclasses are also encouraged to clearly
* specify their match algorithm, and expose the parameters involved in the match
* computation, to allow {@link IQueryable} implementations to optimize their
* execution of the query.
* @since 2.0
*/
public abstract class MatchQuery<T> implements IMatchQuery<T> {
/**
* Returns whether the given object satisfies the parameters of this query.
*
* @param candidate The object to perform the query against
* @return <code>true</code> if the unit satisfies the parameters
* of this query, and <code>false</code> otherwise
*
* @noreference This method is not intended to be referenced by clients.
* Clients should call {@link #perform(Iterator)}
*/
public abstract boolean isMatch(T candidate);
/**
* Performs this query on the given iterator, passing all objects in the iterator
* that match the criteria of this query to the given result.
*/
public final IQueryResult<T> perform(Iterator<T> iterator) {
Collector<T> result = new Collector<T>();
prePerform();
try {
while (iterator.hasNext()) {
T candidate = iterator.next();
if (candidate != null && isMatch(candidate))
if (!result.accept(candidate))
break;
}
} finally {
postPerform();
}
return result;
}
/**
* Execute any pre-processing that must be done before this query is performed against
* a particular iterator. This method may be used by subclasses to do any calculations,
* caching, or other preparation for the query.
* <p>
* This method is internal to the framework. Subclasses may override this method, but
* should not call this method.
*
* @noreference This method is not intended to be referenced by clients.
*/
public void prePerform() {
// nothing to do by default
}
/**
* Execute any post-processing that must be done after this query has been performed against
* a particular iterator. This method may be used by subclasses to clear caches or any other
* cleanup that should occur after a query.
* <p>
* This method will be called even if the query does not complete successfully.
* <p>
* This method is internal to the framework. Subclasses may override this method, but
* should not call this method.
*
* @noreference This method is not intended to be referenced by clients.
*/
public void postPerform() {
// nothing to do by default
}
public IExpression getExpression() {
return null;
}
}
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