org.apache.lucene.util.BitSet.java Source code

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Here is the source code for org.apache.lucene.util.BitSet.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.lucene.util;

import java.io.IOException;

import org.apache.lucene.search.DocIdSetIterator;

/**
 * Base implementation for a bit set.
 * @lucene.internal
 */
public abstract class BitSet implements Bits, Accountable {

    /** Build a {@link BitSet} from the content of the provided {@link DocIdSetIterator}.
     *  NOTE: this will fully consume the {@link DocIdSetIterator}. */
    public static BitSet of(DocIdSetIterator it, int maxDoc) throws IOException {
        final long cost = it.cost();
        final int threshold = maxDoc >>> 7;
        BitSet set;
        if (cost < threshold) {
            set = new SparseFixedBitSet(maxDoc);
        } else {
            set = new FixedBitSet(maxDoc);
        }
        set.or(it);
        return set;
    }

    /** Set the bit at <code>i</code>. */
    public abstract void set(int i);

    /** Clear the bit at <code>i</code>. */
    public abstract void clear(int i);

    /** Clears a range of bits.
     *
     * @param startIndex lower index
     * @param endIndex one-past the last bit to clear
     */
    public abstract void clear(int startIndex, int endIndex);

    /**
     * Return the number of bits that are set.
     * NOTE: this method is likely to run in linear time
     */
    public abstract int cardinality();

    /**
     * Return an approximation of the cardinality of this set. Some
     * implementations may trade accuracy for speed if they have the ability to
     * estimate the cardinality of the set without iterating over all the data.
     * The default implementation returns {@link #cardinality()}.
     */
    public int approximateCardinality() {
        return cardinality();
    }

    /** Returns the index of the last set bit before or on the index specified.
     *  -1 is returned if there are no more set bits.
     */
    public abstract int prevSetBit(int index);

    /** Returns the index of the first set bit starting at the index specified.
     *  {@link DocIdSetIterator#NO_MORE_DOCS} is returned if there are no more set bits.
     */
    public abstract int nextSetBit(int index);

    /** Assert that the current doc is -1. */
    protected final void checkUnpositioned(DocIdSetIterator iter) {
        if (iter.docID() != -1) {
            throw new IllegalStateException(
                    "This operation only works with an unpositioned iterator, got current position = "
                            + iter.docID());
        }
    }

    /** Does in-place OR of the bits provided by the iterator. The state of the
     *  iterator after this operation terminates is undefined. */
    public void or(DocIdSetIterator iter) throws IOException {
        checkUnpositioned(iter);
        for (int doc = iter.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = iter.nextDoc()) {
            set(doc);
        }
    }

}