ParameterizedQuery.java

/**
 * A Query that needs to be bound to a value before it can be executed.
 *
 * The query can take many forms depending on the value which is bound at each
 * time. The same value should always lead to the same query. Normally, before
 * executing the query a concrete value must be set via {@link #setValue(Object)}
 * method although some implementations may decide to return a query even the
 * value is not set.
 */
public abstract class ParameterizedQuery extends Query
{
	private Object value;

	protected ParameterizedQuery()
	{
	}

	@Override
	public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)
		throws IOException
	{
		Query query = this.createQuery(this.value);
		assert query != null;
		return query.createWeight(searcher, scoreMode, boost);
	}

	@Override
	public Query rewrite(IndexReader reader) throws IOException
	{
		Query query = this.createQuery(this.value);
		assert query != null;
		return query.rewrite(reader);
	}

	/**
	 * Creates a query based on the value provided as a parameter.
	 *
	 * It should never return null as long as {@link #setValue(Object)} is
	 * called before. The same value should always generate the same query.
	 * Implementors can decide to return a default query when null is passed as
	 * a value. The method should not be called directly but only via
	 * {@link #createWeight(IndexSearcher, ScoreMode, float)} and
	 * {@link #rewrite(IndexReader)} during the execution of the query.
	 *
	 * @param value
	 * 		the value that is used to generate the query
	 * @return
	 * 		a query based on the provided value
	 *
	 */
	protected abstract Query createQuery(Object value);

	/**
	 * Sets the value that will be used to generate the query.
	 *
	 * The method must be called before executing the query.
	 */
	public final void setValue(Object value)
	{
		this.value = value;
	}

	/**
	 * The query itself is not going to be executed or added to the
	 * {@link QueryCache} so there is no need to provide other equality than the
	 * identity.
	 */
	@Override
	public boolean equals(Object obj)
	{
		return this == obj;
	}

	@Override
	public int hashCode()
	{
		return System.identityHashCode(this);
	}
}