Refactor filter impl

java/org/rocksdb/BloomFilter.java

@@ -0,0 +1,23 @@
+// Copyright (c) 2014, Facebook, Inc.  All rights reserved.
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree. An additional grant
+// of patent rights can be found in the PATENTS file in the same directory.
+
+package org.rocksdb;
+
+public class BloomFilter extends Filter {
+  private final int bitsPerKey_;
+  
+  public BloomFilter(int bitsPerKey) {
+    super();
+    bitsPerKey_ = bitsPerKey;
+    createNewFilter();
+  }
+  
+  @Override
+  protected void createNewFilter() {
+    createNewFilter0(bitsPerKey_);
+  }
+  
+  private native void createNewFilter0(int bitsKeyKey);
+}

java/org/rocksdb/Filter.java

@@ -17,12 +17,10 @@ package org.rocksdb;
  * A good value for bitsPerKey is 10, which yields a filter
  * with ~ 1% false positive rate.
  */
-public class Filter {
-  private long nativeHandle_;
-
-  public Filter(int bitsPerKey) {
-    newFilter(bitsPerKey);
-  }
+public abstract class Filter {
+  protected long nativeHandle_ = 0;
+    
+  protected abstract void createNewFilter();
 
   /**
    * Deletes underlying C++ filter pointer.
@@ -37,10 +35,9 @@ public class Filter {
     dispose();
   }
 
-  private boolean isInitialized() {
+  protected boolean isInitialized() {
     return (nativeHandle_ != 0);
   }
 
-  private native void newFilter(int bitsPerKey);
   private native void dispose0(long handle);
 }