src/java/org/apache/lucene/search/BooleanQuery.java

package org.apache.lucene.search;

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import java.io.IOException;
import java.util.Vector;
import org.apache.lucene.index.IndexReader;

/** A Query that matches documents matching boolean combinations of other
  queries, typically {@link TermQuery}s or {@link PhraseQuery}s.
  */
final public class BooleanQuery extends Query {
  private Vector clauses = new Vector();

  /** Constructs an empty boolean query. */
  public BooleanQuery() {}

  /** Adds a clause to a boolean query.  Clauses may be:
    <ul>
    <li><code>required</code> which means that documents which <i>do not</i>
    match this sub-query will <it>not</it> match the boolean query;
    <li><code>prohibited</code> which means that documents which <i>do</i>
    match this sub-query will <it>not</it> match the boolean query; or
    <li>neither, in which case matched documents are neither prohibited from
    nor required to match the sub-query.
    </ul>
    It is an error to specify a clause as both <code>required</code> and
    <code>prohibited</code>.
    */
  public final void add(Query query, boolean required, boolean prohibited) {
    clauses.addElement(new BooleanClause(query, required, prohibited));
  }

  /** Adds a clause to a boolean query. */
  public final void add(BooleanClause clause) {
    clauses.addElement(clause);
  }

  void prepare(IndexReader reader) {
    for (int i = 0 ; i < clauses.size(); i++) {
      BooleanClause c = (BooleanClause)clauses.elementAt(i);
      c.query.prepare(reader);
    }
  }

  final float sumOfSquaredWeights(Searcher searcher)
       throws IOException {
    float sum = 0.0f;

    for (int i = 0 ; i < clauses.size(); i++) {
      BooleanClause c = (BooleanClause)clauses.elementAt(i);
      if (!c.prohibited)
	sum += c.query.sumOfSquaredWeights(searcher); // sum sub-query weights
    }

    return sum;
  }

  final void normalize(float norm) {
    for (int i = 0 ; i < clauses.size(); i++) {
      BooleanClause c = (BooleanClause)clauses.elementAt(i);
      if (!c.prohibited)
	c.query.normalize(norm);
    }
  }

  final Scorer scorer(IndexReader reader)
       throws IOException {

    if (clauses.size() == 1) {			  // optimize 1-term queries
      BooleanClause c = (BooleanClause)clauses.elementAt(0);
      if (!c.prohibited)			  // just return term scorer
	return c.query.scorer(reader);
    }

    BooleanScorer result = new BooleanScorer();

    for (int i = 0 ; i < clauses.size(); i++) {
      BooleanClause c = (BooleanClause)clauses.elementAt(i);
      Scorer subScorer = c.query.scorer(reader);
      if (subScorer != null)
	result.add(subScorer, c.required, c.prohibited);
      else if (c.required)
	return null;
    }

    return result;
  }

  /** Prints a user-readable version of this query. */
  public String toString(String field) {
    StringBuffer buffer = new StringBuffer();
    for (int i = 0 ; i < clauses.size(); i++) {
      BooleanClause c = (BooleanClause)clauses.elementAt(i);
      if (c.prohibited)
	buffer.append("-");
      else if (c.required)
	buffer.append("+");

      Query subQuery = c.query;
      if (subQuery instanceof BooleanQuery) {	  // wrap sub-bools in parens
	BooleanQuery bq = (BooleanQuery)subQuery;
	buffer.append("(");
	buffer.append(c.query.toString(field));
	buffer.append(")");
      } else
	buffer.append(c.query.toString(field));

      if (i != clauses.size()-1)
	buffer.append(" ");
    }
    return buffer.toString();
  }

}