Add doc

java/org/rocksdb/BloomFilter.java

@@ -5,12 +5,26 @@
 
 package org.rocksdb;
 
+/**
+ * This class creates a new filter policy that uses a bloom filter
+ * with approximately the specified number of bits per key.
+ * A good value for bitsPerKey is 10, which yields a filter
+ * with ~ 1% false positive rate.
+ * 
+ * Default value of bits per key is 10.
+ */
 public class BloomFilter extends Filter {
+  private static final int DEFAULT_BITS_PER_KEY = 10;
   private final int bitsPerKey_;
+    
+  public BloomFilter() {
+    this(DEFAULT_BITS_PER_KEY);
+  }
   
   public BloomFilter(int bitsPerKey) {
     super();
     bitsPerKey_ = bitsPerKey;
+    
     createNewFilter();
   }
   

java/org/rocksdb/Filter.java

@@ -11,11 +11,6 @@ package org.rocksdb;
  * information from disk. In many cases, a filter can cut down the
  * number of disk seeks form a handful to a single disk seek per
  * DB::Get() call.
- *
- * This class creates a new filter policy that uses a bloom filter
- * with approximately the specified number of bits per key.
- * A good value for bitsPerKey is 10, which yields a filter
- * with ~ 1% false positive rate.
  */
 public abstract class Filter {
   protected long nativeHandle_ = 0;