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());