Collections-818: convert to characteristics flag (#329)

src/main/java/org/apache/commons/collections4/bloomfilter/ArrayCountingBloomFilter.java

@@ -110,8 +110,8 @@ public final class ArrayCountingBloomFilter implements CountingBloomFilter {
     }
 
     @Override
-    public boolean isSparse() {
-        return true;
+    public int characteristics() {
+        return SPARSE;
     }
 
     @Override

src/main/java/org/apache/commons/collections4/bloomfilter/BloomFilter.java

@@ -29,6 +29,15 @@ import java.util.Objects;
  */
 public interface BloomFilter extends IndexProducer, BitMapProducer {
 
+    /**
+     * The sparse characteristic used to determine the best method for matching.
+     * <p>For `sparse` implementations
+     * the {@code forEachIndex(IntConsumer consumer)} method is more efficient.  For non `sparse` implementations
+     * the {@code forEachBitMap(LongConsumer consumer)} is more efficient.  Implementers should determine if it is easier
+     * for the implementation to produce indexes of bit map blocks.</p>
+     */
+    int SPARSE = 0x1;
+
     /**
      * Creates a new instance of the BloomFilter with the same properties as the current one.
      * @return a copy of this BloomFilter
@@ -38,17 +47,12 @@ public interface BloomFilter extends IndexProducer, BitMapProducer {
     // Query Operations
 
     /**
-     * This method is used to determine the best method for matching.
-     *
-     * <p>For `sparse` implementations
-     * the {@code forEachIndex(IntConsumer consumer)} method is more efficient.  For non `sparse` implementations
-     * the {@code forEachBitMap(LongConsumer consumer)} is more efficient.  Implementers should determine if it is easier
-     * for the implementation to produce indexes of bit map blocks.</p>
-     *
-     * @return {@code true} if the implementation is sparse {@code false} otherwise.
-     * @see BitMap
+     * Returns the characteristics of the filter.
+     * <p>
+     * Characteristics are defined as bits within the characteristics integer.
+     * @return the characteristics for this bloom filter.
      */
-    boolean isSparse();
+    int characteristics();
 
     /**
      * Gets the shape that was used when the filter was built.
@@ -69,7 +73,7 @@ public interface BloomFilter extends IndexProducer, BitMapProducer {
      */
     default boolean contains(BloomFilter other) {
         Objects.requireNonNull(other, "other");
-        return isSparse() ? contains((IndexProducer) other) : contains((BitMapProducer) other);
+        return (characteristics() & SPARSE) != 0 ? contains((IndexProducer) other) : contains((BitMapProducer) other);
     }
 
     /**
@@ -143,8 +147,8 @@ public interface BloomFilter extends IndexProducer, BitMapProducer {
     default boolean merge(Hasher hasher) {
         Objects.requireNonNull(hasher, "hasher");
         Shape shape = getShape();
-        // create the bloomfilter that is most likely to merge quickly with this one
-        BloomFilter result = isSparse() ? new SparseBloomFilter(shape, hasher) : new SimpleBloomFilter(shape, hasher);
+        // create the Bloom filter that is most likely to merge quickly with this one
+        BloomFilter result = (characteristics() & SPARSE) != 0 ? new SparseBloomFilter(shape, hasher) : new SimpleBloomFilter(shape, hasher);
         return merge(result);
     }
 

src/main/java/org/apache/commons/collections4/bloomfilter/SimpleBloomFilter.java

@@ -65,7 +65,7 @@ public final class SimpleBloomFilter implements BloomFilter {
         this.shape = other.getShape();
         this.bitMap = new long[BitMap.numberOfBitMaps(shape.getNumberOfBits())];
         this.cardinality = 0;
-        if (other.isSparse()) {
+        if ((other.characteristics() & SPARSE) != 0) {
             merge((IndexProducer) other);
         } else {
             merge((BitMapProducer) other);
@@ -194,7 +194,7 @@ public final class SimpleBloomFilter implements BloomFilter {
     @Override
     public boolean merge(BloomFilter other) {
         Objects.requireNonNull(other, "other");
-        if (other.isSparse()) {
+        if ((other.characteristics() & SPARSE) != 0) {
             merge((IndexProducer) other);
         } else {
             merge((BitMapProducer) other);
@@ -208,8 +208,8 @@ public final class SimpleBloomFilter implements BloomFilter {
     }
 
     @Override
-    public boolean isSparse() {
-        return false;
+    public int characteristics() {
+        return 0;
     }
 
     @Override

src/main/java/org/apache/commons/collections4/bloomfilter/SparseBloomFilter.java

@@ -58,7 +58,7 @@ public final class SparseBloomFilter implements BloomFilter {
         Objects.requireNonNull(other, "other");
         this.shape = other.getShape();
         this.indices = new TreeSet<>();
-        if (other.isSparse()) {
+        if ((other.characteristics() & SPARSE) != 0) {
             merge((IndexProducer) other);
         } else {
             merge(IndexProducer.fromBitMapProducer(other));
@@ -169,7 +169,7 @@ public final class SparseBloomFilter implements BloomFilter {
     @Override
     public boolean merge(BloomFilter other) {
         Objects.requireNonNull(other, "other");
-        IndexProducer producer = other.isSparse() ? (IndexProducer) other : IndexProducer.fromBitMapProducer(other);
+        IndexProducer producer = (other.characteristics() & SPARSE) != 0 ? (IndexProducer) other : IndexProducer.fromBitMapProducer(other);
         merge(producer);
         return true;
     }
@@ -180,8 +180,8 @@ public final class SparseBloomFilter implements BloomFilter {
     }
 
     @Override
-    public boolean isSparse() {
-        return true;
+    public int characteristics() {
+        return SPARSE;
     }
 
     @Override

src/test/java/org/apache/commons/collections4/bloomfilter/DefaultBloomFilterTest.java

@@ -186,8 +186,8 @@ public class DefaultBloomFilterTest extends AbstractBloomFilterTest<DefaultBloom
         }
 
         @Override
-        public boolean isSparse() {
-            return true;
+        public int characteristics() {
+            return SPARSE;
         }
 
         @Override
@@ -217,8 +217,8 @@ public class DefaultBloomFilterTest extends AbstractBloomFilterTest<DefaultBloom
         }
 
         @Override
-        public boolean isSparse() {
-            return false;
+        public int characteristics() {
+            return 0;
         }
 
         @Override