Add support for intersection to BloomFilter.

src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java

@@ -144,6 +144,27 @@ public Filter merge(Filter... filters) {
  return merged;
  }
 
+ public void intersectInPlace(BloomFilter other) {
+ if (this.getHashCount() != other.getHashCount()) {
+ throw new IllegalArgumentException("Cannot intersect filters of different sizes");
+ }
+ this.filter().and(other.filter());
+ }
+
+ public BloomFilter intersect(BloomFilter... filters) {
+ BloomFilter intersected = new BloomFilter(this.getHashCount(), (BitSet) this.filter().clone());
+
+ if (filters == null) {
+ return intersected;
+ }
+
+ for (BloomFilter filter : filters) {
+ intersected.intersectInPlace(filter);
+ }
+
+ return intersected;
+ }
+
  /**
  * @return a BloomFilter that always returns a positive match, for testing
  */

src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java

@@ -84,6 +84,54 @@ public void testMergeException() {
  BloomFilter mergeBf = (BloomFilter) bf3.merge(bf);
  }
 
+ @Test
+ public void testIntersectInPlace() {
+ BloomFilter bf3 = new BloomFilter(ELEMENTS, spec.bucketsPerElement);
+ for (int i = 0; i < 20; ++i) {
+ bf.add(Integer.toString(i));
+ }
+ for (int i = 10; i < 30; ++i) {
+ bf2.add(Integer.toString(i));
+ }
+ for (int i = 10; i < 20; ++i) {
+ bf3.add(Integer.toString(i));
+ }
+ bf.intersectInPlace(bf2);
+ for (int i = 0; i < 30; ++i) {
+ String iString = Integer.toString(i);
+ if (bf3.isPresent(iString)) {
+ assertTrue(bf.isPresent(iString));
+ } else {
+ assertFalse(bf.isPresent(iString));
+ }
+ }
+ }
+
+ @Test(expected=IllegalArgumentException.class)
+ public void testIntersectInPlaceException() {
+ BloomFilter bf3 = new BloomFilter(ELEMENTS*10, 1);
+ bf3.intersectInPlace(bf);
+ }
+
+ @Test
+ public void testIntersect() {
+ for (int i = 0; i < 20; ++i) {
+ bf.add(Integer.toString(i));
+ }
+ for (int i = 10; i < 30; ++i) {
+ bf2.add(Integer.toString(i));
+ }
+ BloomFilter bf3 = bf.intersect(bf2);
+ for (int i = 0; i < 30; ++i) {
+ String iString = Integer.toString(i);
+ if (bf.isPresent(iString) && bf2.isPresent(iString)) {
+ assertTrue(bf3.isPresent(iString));
+ } else {
+ assertFalse(bf3.isPresent(iString));
+ }
+ }
+ }
+
  @Test
  public void testFalsePositivesInt() {
  FilterTest.testFalsePositives(bf, FilterTest.intKeys(), FilterTest.randomKeys2());