diff --git a/java/src/com/android/inputmethod/keyboard/Key.java b/java/src/com/android/inputmethod/keyboard/Key.java
index 01fa02e..143c6e8 100644
--- a/java/src/com/android/inputmethod/keyboard/Key.java
+++ b/java/src/com/android/inputmethod/keyboard/Key.java
@@ -234,7 +234,7 @@
     public Key(final Resources res, final KeyboardParams params, final KeyboardRow row,
             final XmlPullParser parser) throws XmlPullParserException {
         final float horizontalGap = isSpacer() ? 0 : params.mHorizontalGap;
-        final int rowHeight = row.mRowHeight;
+        final int rowHeight = row.getRowHeight();
         mHeight = rowHeight - params.mVerticalGap;
 
         final TypedArray keyAttr = res.obtainAttributes(Xml.asAttributeSet(parser),
diff --git a/java/src/com/android/inputmethod/keyboard/internal/KeyboardBuilder.java b/java/src/com/android/inputmethod/keyboard/internal/KeyboardBuilder.java
index 9bc52e5..65eb171 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/KeyboardBuilder.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/KeyboardBuilder.java
@@ -745,7 +745,7 @@
             mRightEdgeKey = null;
         }
         addEdgeSpace(mParams.mRightPadding, row);
-        mCurrentY += row.mRowHeight;
+        mCurrentY += row.getRowHeight();
         mCurrentRow = null;
         mTopEdge = false;
     }
diff --git a/java/src/com/android/inputmethod/keyboard/internal/KeyboardRow.java b/java/src/com/android/inputmethod/keyboard/internal/KeyboardRow.java
index edfcec7..80fe1ea 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/KeyboardRow.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/KeyboardRow.java
@@ -38,10 +38,10 @@
     private static final int KEYWIDTH_FILL_RIGHT = -1;
 
     private final KeyboardParams mParams;
+    /** The height of this row. */
+    private final int mRowHeight;
     /** Default width of a key in this row. */
     private float mDefaultKeyWidth;
-    /** Default height of a key in this row. */
-    public final int mRowHeight;
     /** Default keyLabelFlags in this row. */
     private int mDefaultKeyLabelFlags;
     /** Default backgroundType for this row */
@@ -74,6 +74,10 @@
         mCurrentX = 0.0f;
     }
 
+    public int getRowHeight() {
+        return mRowHeight;
+    }
+
     public float getDefaultKeyWidth() {
         return mDefaultKeyWidth;
     }
diff --git a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
index 3f11391..b481371 100644
--- a/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
+++ b/java/src/com/android/inputmethod/latin/ExpandableBinaryDictionary.java
@@ -84,6 +84,9 @@
     /** Controls access to the local binary dictionary for this instance. */
     private final DictionaryController mLocalDictionaryController = new DictionaryController();
 
+    /* A extension for a binary dictionary file. */
+    public static final String DICT_FILE_EXTENSION = ".dict";
+
     /**
      * Abstract method for loading the unigrams and bigrams of a given dictionary in a background
      * thread.
@@ -129,7 +132,7 @@
     }
 
     protected static String getFilenameWithLocale(final String name, final String localeStr) {
-        return name + "." + localeStr + ".dict";
+        return name + "." + localeStr + DICT_FILE_EXTENSION;
     }
 
     /**
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoder.java
index 8d68c7e..5e3d6d2 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoder.java
@@ -22,6 +22,7 @@
 import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
 import com.android.inputmethod.latin.makedict.FusionDictionary.PtNodeArray;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+import com.android.inputmethod.latin.makedict.decoder.HeaderReaderInterface;
 import com.android.inputmethod.latin.utils.JniUtils;
 
 import java.io.ByteArrayOutputStream;
@@ -250,7 +251,7 @@
         /**
          * Reads a string from a buffer. This is the converse of the above method.
          */
-        private static String readString(final FusionDictionaryBufferInterface buffer) {
+        static String readString(final FusionDictionaryBufferInterface buffer) {
             final StringBuilder s = new StringBuilder();
             int character = readChar(buffer);
             while (character != FormatSpec.INVALID_CHARACTER) {
@@ -629,7 +630,7 @@
      * @throws UnsupportedFormatException
      * @throws IOException
      */
-    private static int checkFormatVersion(final FusionDictionaryBufferInterface buffer)
+    static int checkFormatVersion(final FusionDictionaryBufferInterface buffer)
             throws IOException, UnsupportedFormatException {
         final int version = getFormatVersion(buffer);
         if (version < FormatSpec.MINIMUM_SUPPORTED_VERSION
@@ -643,25 +644,22 @@
 
     /**
      * Reads a header from a buffer.
-     * @param buffer the buffer to read.
+     * @param headerReader the header reader
      * @throws IOException
      * @throws UnsupportedFormatException
      */
-    public static FileHeader readHeader(final FusionDictionaryBufferInterface buffer)
+    public static FileHeader readHeader(final HeaderReaderInterface headerReader)
             throws IOException, UnsupportedFormatException {
-        final int version = checkFormatVersion(buffer);
-        final int optionsFlags = buffer.readUnsignedShort();
+        final int version = headerReader.readVersion();
+        final int optionsFlags = headerReader.readOptionFlags();
 
-        final HashMap<String, String> attributes = new HashMap<String, String>();
-        final int headerSize;
-        headerSize = buffer.readInt();
+        final int headerSize = headerReader.readHeaderSize();
 
         if (headerSize < 0) {
             throw new UnsupportedFormatException("header size can't be negative.");
         }
 
-        populateOptions(buffer, headerSize, attributes);
-        buffer.position(headerSize);
+        final HashMap<String, String> attributes = headerReader.readAttributes(headerSize);
 
         final FileHeader header = new FileHeader(headerSize,
                 new FusionDictionary.DictionaryOptions(attributes,
@@ -711,14 +709,14 @@
         }
 
         // Read header
-        final FileHeader header = readHeader(reader.getBuffer());
+        final FileHeader fileHeader = readHeader(reader);
 
         Map<Integer, PtNodeArray> reverseNodeArrayMapping = new TreeMap<Integer, PtNodeArray>();
         Map<Integer, CharGroup> reverseGroupMapping = new TreeMap<Integer, CharGroup>();
-        final PtNodeArray root = readNodeArray(reader.getBuffer(), header.mHeaderSize,
-                reverseNodeArrayMapping, reverseGroupMapping, header.mFormatOptions);
+        final PtNodeArray root = readNodeArray(reader.getBuffer(), fileHeader.mHeaderSize,
+                reverseNodeArrayMapping, reverseGroupMapping, fileHeader.mFormatOptions);
 
-        FusionDictionary newDict = new FusionDictionary(root, header.mDictionaryOptions);
+        FusionDictionary newDict = new FusionDictionary(root, fileHeader.mDictionaryOptions);
         if (null != dict) {
             for (final Word w : dict) {
                 if (w.mIsBlacklistEntry) {
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
index 9aa39e0..e5735aa 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
@@ -24,13 +24,13 @@
 import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
 import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+import com.android.inputmethod.latin.utils.ByteArrayWrapper;
 
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.OutputStream;
-import java.nio.channels.FileChannel;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.Map;
@@ -141,20 +141,20 @@
      * Reads unigrams and bigrams from the binary file.
      * Doesn't store a full memory representation of the dictionary.
      *
-     * @param reader the reader.
+     * @param dictReader the dict reader.
      * @param words the map to store the address as a key and the word as a value.
      * @param frequencies the map to store the address as a key and the frequency as a value.
      * @param bigrams the map to store the address as a key and the list of address as a value.
      * @throws IOException if the file can't be read.
      * @throws UnsupportedFormatException if the format of the file is not recognized.
      */
-    public static void readUnigramsAndBigramsBinary(final BinaryDictReader reader,
+    public static void readUnigramsAndBigramsBinary(final BinaryDictReader dictReader,
             final Map<Integer, String> words, final Map<Integer, Integer> frequencies,
             final Map<Integer, ArrayList<PendingAttribute>> bigrams) throws IOException,
             UnsupportedFormatException {
         // Read header
-        final FileHeader header = BinaryDictDecoder.readHeader(reader.getBuffer());
-        readUnigramsAndBigramsBinaryInner(reader.getBuffer(), header.mHeaderSize, words,
+        final FileHeader header = BinaryDictDecoder.readHeader(dictReader);
+        readUnigramsAndBigramsBinaryInner(dictReader.getBuffer(), header.mHeaderSize, words,
                 frequencies, bigrams, header.mFormatOptions);
     }
 
@@ -162,20 +162,20 @@
      * Gets the address of the last CharGroup of the exact matching word in the dictionary.
      * If no match is found, returns NOT_VALID_WORD.
      *
-     * @param reader the reader.
+     * @param dictReader the dict reader.
      * @param word the word we search for.
      * @return the address of the terminal node.
      * @throws IOException if the file can't be read.
      * @throws UnsupportedFormatException if the format of the file is not recognized.
      */
     @UsedForTesting
-    public static int getTerminalPosition(final BinaryDictReader reader,
+    public static int getTerminalPosition(final BinaryDictReader dictReader,
             final String word) throws IOException, UnsupportedFormatException {
-        final FusionDictionaryBufferInterface buffer = reader.getBuffer();
+        final FusionDictionaryBufferInterface buffer = dictReader.getBuffer();
         if (word == null) return FormatSpec.NOT_VALID_WORD;
         if (buffer.position() != 0) buffer.position(0);
 
-        final FileHeader header = BinaryDictDecoder.readHeader(buffer);
+        final FileHeader header = BinaryDictDecoder.readHeader(dictReader);
         int wordPos = 0;
         final int wordLen = word.codePointCount(0, word.length());
         for (int depth = 0; depth < Constants.DICTIONARY_MAX_WORD_LENGTH; ++depth) {
@@ -510,20 +510,20 @@
     /**
      * Find a word using the BinaryDictReader.
      *
-     * @param reader the reader
+     * @param dictReader the dict reader
      * @param word the word searched
      * @return the found group
      * @throws IOException
      * @throws UnsupportedFormatException
      */
     @UsedForTesting
-    public static CharGroupInfo findWordByBinaryDictReader(final BinaryDictReader reader,
+    public static CharGroupInfo findWordByBinaryDictReader(final BinaryDictReader dictReader,
             final String word) throws IOException, UnsupportedFormatException {
-        int position = getTerminalPosition(reader, word);
-        final FusionDictionaryBufferInterface buffer = reader.getBuffer();
+        int position = getTerminalPosition(dictReader, word);
+        final FusionDictionaryBufferInterface buffer = dictReader.getBuffer();
         if (position != FormatSpec.NOT_VALID_WORD) {
             buffer.position(0);
-            final FileHeader header = BinaryDictDecoder.readHeader(buffer);
+            final FileHeader header = BinaryDictDecoder.readHeader(dictReader);
             buffer.position(position);
             return BinaryDictDecoder.readCharGroup(buffer, position, header.mFormatOptions);
         }
@@ -544,16 +544,21 @@
             final File file, final long offset, final long length)
             throws FileNotFoundException, IOException, UnsupportedFormatException {
         final byte[] buffer = new byte[HEADER_READING_BUFFER_SIZE];
-        final FileInputStream inStream = new FileInputStream(file);
-        try {
-            inStream.read(buffer);
-            final BinaryDictDecoder.ByteBufferWrapper wrapper =
-                    new BinaryDictDecoder.ByteBufferWrapper(inStream.getChannel().map(
-                            FileChannel.MapMode.READ_ONLY, offset, length));
-            return BinaryDictDecoder.readHeader(wrapper);
-        } finally {
-            inStream.close();
-        }
+        final BinaryDictReader dictReader = new BinaryDictReader(file);
+        dictReader.openBuffer(new BinaryDictReader.FusionDictionaryBufferFactory() {
+            @Override
+            public FusionDictionaryBufferInterface getFusionDictionaryBuffer(File file)
+                    throws FileNotFoundException, IOException {
+                final FileInputStream inStream = new FileInputStream(file);
+                try {
+                    inStream.read(buffer);
+                    return new ByteArrayWrapper(buffer);
+                } finally {
+                    inStream.close();
+                }
+            }
+        });
+        return BinaryDictDecoder.readHeader(dictReader);
     }
 
     public static FileHeader getDictionaryFileHeaderOrNull(final File file, final long offset,
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java
index f2f3c46..6d3b31a 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java
@@ -17,7 +17,9 @@
 package com.android.inputmethod.latin.makedict;
 
 import com.android.inputmethod.annotations.UsedForTesting;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder.CharEncoding;
 import com.android.inputmethod.latin.makedict.BinaryDictDecoder.FusionDictionaryBufferInterface;
+import com.android.inputmethod.latin.makedict.decoder.HeaderReaderInterface;
 import com.android.inputmethod.latin.utils.ByteArrayWrapper;
 
 import java.io.File;
@@ -27,8 +29,9 @@
 import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
+import java.util.HashMap;
 
-public class BinaryDictReader {
+public class BinaryDictReader implements HeaderReaderInterface {
 
     public interface FusionDictionaryBufferFactory {
         public FusionDictionaryBufferInterface getFusionDictionaryBuffer(final File file)
@@ -133,4 +136,34 @@
         openBuffer(factory);
         return getBuffer();
     }
+
+    // The implementation of HeaderReaderInterface
+    @Override
+    public int readVersion() throws IOException, UnsupportedFormatException {
+        return BinaryDictDecoder.checkFormatVersion(mFusionDictionaryBuffer);
+    }
+
+    @Override
+    public int readOptionFlags() {
+        return mFusionDictionaryBuffer.readUnsignedShort();
+    }
+
+    @Override
+    public int readHeaderSize() {
+        return mFusionDictionaryBuffer.readInt();
+    }
+
+    @Override
+    public HashMap<String, String> readAttributes(final int headerSize) {
+        final HashMap<String, String> attributes = new HashMap<String, String>();
+        while (mFusionDictionaryBuffer.position() < headerSize) {
+            // We can avoid infinite loop here since mFusionDictonary.position() is always increased
+            // by calling CharEncoding.readString.
+            final String key = CharEncoding.readString(mFusionDictionaryBuffer);
+            final String value = CharEncoding.readString(mFusionDictionaryBuffer);
+            attributes.put(key, value);
+        }
+        mFusionDictionaryBuffer.position(headerSize);
+        return attributes;
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
index 11f9f8a..584b793 100644
--- a/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
@@ -49,18 +49,18 @@
     /**
      * Delete the word from the binary file.
      *
-     * @param reader the reader.
+     * @param dictReader the dict reader.
      * @param word the word we delete
      * @throws IOException
      * @throws UnsupportedFormatException
      */
     @UsedForTesting
-    public static void deleteWord(final BinaryDictReader reader, final String word)
+    public static void deleteWord(final BinaryDictReader dictReader, final String word)
             throws IOException, UnsupportedFormatException {
-        final FusionDictionaryBufferInterface buffer = reader.getBuffer();
+        final FusionDictionaryBufferInterface buffer = dictReader.getBuffer();
         buffer.position(0);
-        final FileHeader header = BinaryDictDecoder.readHeader(buffer);
-        final int wordPosition = BinaryDictIOUtils.getTerminalPosition(reader, word);
+        final FileHeader header = BinaryDictDecoder.readHeader(dictReader);
+        final int wordPosition = BinaryDictIOUtils.getTerminalPosition(dictReader, word);
         if (wordPosition == FormatSpec.NOT_VALID_WORD) return;
 
         buffer.position(wordPosition);
@@ -236,7 +236,7 @@
     /**
      * Insert a word into a binary dictionary.
      *
-     * @param reader the reader.
+     * @param dictReader the dict reader.
      * @param destination a stream to the underlying file, with the pointer at the end of the file.
      * @param word the word to insert.
      * @param frequency the frequency of the new word.
@@ -249,16 +249,16 @@
     // TODO: Support batch insertion.
     // TODO: Remove @UsedForTesting once UserHistoryDictionary is implemented by BinaryDictionary.
     @UsedForTesting
-    public static void insertWord(final BinaryDictReader reader, final OutputStream destination,
+    public static void insertWord(final BinaryDictReader dictReader, final OutputStream destination,
             final String word, final int frequency, final ArrayList<WeightedString> bigramStrings,
             final ArrayList<WeightedString> shortcuts, final boolean isNotAWord,
             final boolean isBlackListEntry)
                     throws IOException, UnsupportedFormatException {
         final ArrayList<PendingAttribute> bigrams = new ArrayList<PendingAttribute>();
-        final FusionDictionaryBufferInterface buffer = reader.getBuffer();
+        final FusionDictionaryBufferInterface buffer = dictReader.getBuffer();
         if (bigramStrings != null) {
             for (final WeightedString bigram : bigramStrings) {
-                int position = BinaryDictIOUtils.getTerminalPosition(reader, bigram.mWord);
+                int position = BinaryDictIOUtils.getTerminalPosition(dictReader, bigram.mWord);
                 if (position == FormatSpec.NOT_VALID_WORD) {
                     // TODO: figure out what is the correct thing to do here.
                 } else {
@@ -273,7 +273,7 @@
 
         // find the insert position of the word.
         if (buffer.position() != 0) buffer.position(0);
-        final FileHeader header = BinaryDictDecoder.readHeader(buffer);
+        final FileHeader fileHeader = BinaryDictDecoder.readHeader(dictReader);
 
         int wordPos = 0, address = buffer.position(), nodeOriginAddress = buffer.position();
         final int[] codePoints = FusionDictionary.getCodePoints(word);
@@ -289,9 +289,9 @@
             for (int i = 0; i < charGroupCount; ++i) {
                 address = buffer.position();
                 final CharGroupInfo currentInfo = BinaryDictDecoder.readCharGroup(buffer,
-                        buffer.position(), header.mFormatOptions);
+                        buffer.position(), fileHeader.mFormatOptions);
                 final boolean isMovedGroup = BinaryDictIOUtils.isMovedGroup(currentInfo.mFlags,
-                        header.mFormatOptions);
+                        fileHeader.mFormatOptions);
                 if (isMovedGroup) continue;
                 nodeParentAddress = (currentInfo.mParentAddress == FormatSpec.NO_PARENT_ADDRESS)
                         ? FormatSpec.NO_PARENT_ADDRESS : currentInfo.mParentAddress + address;
@@ -311,16 +311,16 @@
                         final int newNodeAddress = buffer.limit();
                         final int flags = BinaryDictEncoder.makeCharGroupFlags(p > 1,
                                 isTerminal, 0, hasShortcuts, hasBigrams, false /* isNotAWord */,
-                                false /* isBlackListEntry */, header.mFormatOptions);
+                                false /* isBlackListEntry */, fileHeader.mFormatOptions);
                         int written = moveGroup(newNodeAddress, currentInfo.mCharacters, p, flags,
                                 frequency, nodeParentAddress, shortcuts, bigrams, destination,
-                                buffer, nodeOriginAddress, address, header.mFormatOptions);
+                                buffer, nodeOriginAddress, address, fileHeader.mFormatOptions);
 
                         final int[] characters2 = Arrays.copyOfRange(currentInfo.mCharacters, p,
                                 currentInfo.mCharacters.length);
                         if (currentInfo.mChildrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
                             updateParentAddresses(buffer, currentInfo.mChildrenAddress,
-                                    newNodeAddress + written + 1, header.mFormatOptions);
+                                    newNodeAddress + written + 1, fileHeader.mFormatOptions);
                         }
                         final CharGroupInfo newInfo2 = new CharGroupInfo(
                                 newNodeAddress + written + 1, -1 /* endAddress */,
@@ -352,17 +352,17 @@
                                     false /* isTerminal */, 0 /* childrenAddressSize*/,
                                     false /* hasShortcut */, false /* hasBigrams */,
                                     false /* isNotAWord */, false /* isBlackListEntry */,
-                                    header.mFormatOptions);
+                                    fileHeader.mFormatOptions);
                             int written = moveGroup(newNodeAddress, currentInfo.mCharacters, p,
                                     prefixFlags, -1 /* frequency */, nodeParentAddress, null, null,
                                     destination, buffer, nodeOriginAddress, address,
-                                    header.mFormatOptions);
+                                    fileHeader.mFormatOptions);
 
                             final int[] suffixCharacters = Arrays.copyOfRange(
                                     currentInfo.mCharacters, p, currentInfo.mCharacters.length);
                             if (currentInfo.mChildrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
                                 updateParentAddresses(buffer, currentInfo.mChildrenAddress,
-                                        newNodeAddress + written + 1, header.mFormatOptions);
+                                        newNodeAddress + written + 1, fileHeader.mFormatOptions);
                             }
                             final int suffixFlags = BinaryDictEncoder.makeCharGroupFlags(
                                     suffixCharacters.length > 1,
@@ -371,21 +371,21 @@
                                     (currentInfo.mFlags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS)
                                             != 0,
                                     (currentInfo.mFlags & FormatSpec.FLAG_HAS_BIGRAMS) != 0,
-                                    isNotAWord, isBlackListEntry, header.mFormatOptions);
+                                    isNotAWord, isBlackListEntry, fileHeader.mFormatOptions);
                             final CharGroupInfo suffixInfo = new CharGroupInfo(
                                     newNodeAddress + written + 1, -1 /* endAddress */, suffixFlags,
                                     suffixCharacters, currentInfo.mFrequency, newNodeAddress + 1,
                                     currentInfo.mChildrenAddress, currentInfo.mShortcutTargets,
                                     currentInfo.mBigrams);
                             written += BinaryDictIOUtils.computeGroupSize(suffixInfo,
-                                    header.mFormatOptions) + 1;
+                                    fileHeader.mFormatOptions) + 1;
 
                             final int[] newCharacters = Arrays.copyOfRange(codePoints, wordPos + p,
                                     codePoints.length);
                             final int flags = BinaryDictEncoder.makeCharGroupFlags(
                                     newCharacters.length > 1, isTerminal,
                                     0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
-                                    isNotAWord, isBlackListEntry, header.mFormatOptions);
+                                    isNotAWord, isBlackListEntry, fileHeader.mFormatOptions);
                             final CharGroupInfo newInfo = new CharGroupInfo(
                                     newNodeAddress + written, -1 /* endAddress */, flags,
                                     newCharacters, frequency, newNodeAddress + 1,
@@ -407,13 +407,13 @@
                         final boolean hasMultipleChars = currentInfo.mCharacters.length > 1;
                         final int flags = BinaryDictEncoder.makeCharGroupFlags(hasMultipleChars,
                                 isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
-                                isNotAWord, isBlackListEntry, header.mFormatOptions);
+                                isNotAWord, isBlackListEntry, fileHeader.mFormatOptions);
                         final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
                                 -1 /* endAddress */, flags, currentInfo.mCharacters, frequency,
                                 nodeParentAddress, currentInfo.mChildrenAddress, shortcuts,
                                 bigrams);
                         moveCharGroup(destination, buffer, newInfo, nodeOriginAddress, address,
-                                header.mFormatOptions);
+                                fileHeader.mFormatOptions);
                         return;
                     }
                     wordPos += currentInfo.mCharacters.length;
@@ -432,12 +432,12 @@
                          */
                         final int newNodeAddress = buffer.limit();
                         updateChildrenAddress(buffer, address, newNodeAddress,
-                                header.mFormatOptions);
+                                fileHeader.mFormatOptions);
                         final int newGroupAddress = newNodeAddress + 1;
                         final boolean hasMultipleChars = (wordLen - wordPos) > 1;
                         final int flags = BinaryDictEncoder.makeCharGroupFlags(hasMultipleChars,
                                 isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
-                                isNotAWord, isBlackListEntry, header.mFormatOptions);
+                                isNotAWord, isBlackListEntry, fileHeader.mFormatOptions);
                         final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
                         final CharGroupInfo newInfo = new CharGroupInfo(newGroupAddress, -1, flags,
                                 characters, frequency, address, FormatSpec.NO_CHILDREN_ADDRESS,
@@ -482,7 +482,7 @@
                 final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
                 final int flags = BinaryDictEncoder.makeCharGroupFlags(characters.length > 1,
                         isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
-                        isNotAWord, isBlackListEntry, header.mFormatOptions);
+                        isNotAWord, isBlackListEntry, fileHeader.mFormatOptions);
                 final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
                         -1 /* endAddress */, flags, characters, frequency, nodeParentAddress,
                         FormatSpec.NO_CHILDREN_ADDRESS, shortcuts, bigrams);
diff --git a/java/src/com/android/inputmethod/latin/makedict/decoder/HeaderReaderInterface.java b/java/src/com/android/inputmethod/latin/makedict/decoder/HeaderReaderInterface.java
new file mode 100644
index 0000000..7cddef2
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/makedict/decoder/HeaderReaderInterface.java
@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.latin.makedict.decoder;
+
+import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
+
+import java.io.IOException;
+import java.util.HashMap;
+
+/**
+ * An interface to read a binary dictionary file header.
+ */
+public interface HeaderReaderInterface {
+    public int readVersion() throws IOException, UnsupportedFormatException;
+    public int readOptionFlags();
+    public int readHeaderSize();
+    public HashMap<String, String> readAttributes(final int headerSize);
+}
diff --git a/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java b/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java
index 955bd27..a038d0a 100644
--- a/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/personalization/PersonalizationPredictionDictionary.java
@@ -17,6 +17,7 @@
 package com.android.inputmethod.latin.personalization;
 
 import com.android.inputmethod.latin.Dictionary;
+import com.android.inputmethod.latin.ExpandableBinaryDictionary;
 
 import android.content.Context;
 import android.content.SharedPreferences;
@@ -31,6 +32,6 @@
 
     @Override
     protected String getDictionaryFileName() {
-        return NAME + "." + getLocale() + ".dict";
+        return NAME + "." + getLocale() + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
     }
 }
diff --git a/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java b/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
index b8db75f..76e48c7 100644
--- a/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/personalization/UserHistoryPredictionDictionary.java
@@ -17,6 +17,7 @@
 package com.android.inputmethod.latin.personalization;
 
 import com.android.inputmethod.latin.Dictionary;
+import com.android.inputmethod.latin.ExpandableBinaryDictionary;
 
 import android.content.Context;
 import android.content.SharedPreferences;
@@ -35,6 +36,6 @@
 
     @Override
     protected String getDictionaryFileName() {
-        return NAME + "." + getLocale() + ".dict";
+        return NAME + "." + getLocale() + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
     }
 }
diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
index e98790b..be468c1 100644
--- a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderEncoderTests.java
@@ -71,6 +71,8 @@
     private static final FormatSpec.FormatOptions VERSION3_WITH_DYNAMIC_UPDATE =
             new FormatSpec.FormatOptions(3, true /* supportsDynamicUpdate */);
 
+    private static final String TEST_DICT_FILE_EXTENSION = ".testDict";
+
     public BinaryDictDecoderEncoderTests() {
         this(System.currentTimeMillis(), DEFAULT_MAX_UNIGRAMS);
     }
@@ -293,7 +295,8 @@
             final String message) {
         File file = null;
         try {
-            file = File.createTempFile("runReadAndWrite", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("runReadAndWrite", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             Log.e(TAG, "IOException", e);
         }
@@ -435,7 +438,8 @@
             final FormatSpec.FormatOptions formatOptions, final String message) {
         File file = null;
         try {
-            file = File.createTempFile("runReadUnigrams", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("runReadUnigrams", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             Log.e(TAG, "IOException", e);
         }
@@ -493,21 +497,21 @@
     }
 
     // Tests for getTerminalPosition
-    private String getWordFromBinary(final BinaryDictReader reader, final int address) {
-        final FusionDictionaryBufferInterface buffer = reader.getBuffer();
+    private String getWordFromBinary(final BinaryDictReader dictReader, final int address) {
+        final FusionDictionaryBufferInterface buffer = dictReader.getBuffer();
         if (buffer.position() != 0) buffer.position(0);
 
-        FileHeader header = null;
+        FileHeader fileHeader = null;
         try {
-            header = BinaryDictDecoder.readHeader(buffer);
+            fileHeader = BinaryDictDecoder.readHeader(dictReader);
         } catch (IOException e) {
             return null;
         } catch (UnsupportedFormatException e) {
             return null;
         }
-        if (header == null) return null;
-        return BinaryDictDecoder.getWordAtAddress(buffer, header.mHeaderSize,
-                address - header.mHeaderSize, header.mFormatOptions).mWord;
+        if (fileHeader == null) return null;
+        return BinaryDictDecoder.getWordAtAddress(buffer, fileHeader.mHeaderSize,
+                address - fileHeader.mHeaderSize, fileHeader.mFormatOptions).mWord;
     }
 
     private long runGetTerminalPosition(final BinaryDictReader reader, final String word, int index,
@@ -533,7 +537,7 @@
     public void testGetTerminalPosition() {
         File file = null;
         try {
-            file = File.createTempFile("testGetTerminalPosition", ".dict",
+            file = File.createTempFile("testGetTerminalPosition", TEST_DICT_FILE_EXTENSION,
                     getContext().getCacheDir());
         } catch (IOException e) {
             // do nothing
@@ -593,7 +597,8 @@
     public void testDeleteWord() {
         File file = null;
         try {
-            file = File.createTempFile("testDeleteWord", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testDeleteWord", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             // do nothing
         }
diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
index 300fd6a..bcf2c31 100644
--- a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtilsTests.java
@@ -48,6 +48,8 @@
     public static final int DEFAULT_MAX_UNIGRAMS = 1500;
     private final int mMaxUnigrams;
 
+    private static final String TEST_DICT_FILE_EXTENSION = ".testDict";
+
     private static final String[] CHARACTERS = {
         "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",
         "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z",
@@ -126,22 +128,24 @@
         }
     }
 
-    private static void printBinaryFile(final FusionDictionaryBufferInterface buffer)
+    private static void printBinaryFile(final BinaryDictReader dictReader)
             throws IOException, UnsupportedFormatException {
-        FileHeader header = BinaryDictDecoder.readHeader(buffer);
+        final FileHeader fileHeader = BinaryDictDecoder.readHeader(dictReader);
+        final FusionDictionaryBufferInterface buffer = dictReader.getBuffer();
         while (buffer.position() < buffer.limit()) {
-            printNode(buffer, header.mFormatOptions);
+            printNode(buffer, fileHeader.mFormatOptions);
         }
     }
 
     private int getWordPosition(final File file, final String word) {
         int position = FormatSpec.NOT_VALID_WORD;
-        final BinaryDictReader reader = new BinaryDictReader(file);
+        final BinaryDictReader dictReader = new BinaryDictReader(file);
         FileInputStream inStream = null;
         try {
             inStream = new FileInputStream(file);
-            reader.openBuffer(new BinaryDictReader.FusionDictionaryBufferFromByteBufferFactory());
-            position = BinaryDictIOUtils.getTerminalPosition(reader, word);
+            dictReader.openBuffer(
+                    new BinaryDictReader.FusionDictionaryBufferFromByteBufferFactory());
+            position = BinaryDictIOUtils.getTerminalPosition(dictReader, word);
         } catch (IOException e) {
         } catch (UnsupportedFormatException e) {
         } finally {
@@ -157,11 +161,12 @@
     }
 
     private CharGroupInfo findWordFromFile(final File file, final String word) {
-        final BinaryDictReader reader = new BinaryDictReader(file);
+        final BinaryDictReader dictReader = new BinaryDictReader(file);
         CharGroupInfo info = null;
         try {
-            reader.openBuffer(new BinaryDictReader.FusionDictionaryBufferFromByteBufferFactory());
-            info = BinaryDictIOUtils.findWordByBinaryDictReader(reader, word);
+            dictReader.openBuffer(
+                    new BinaryDictReader.FusionDictionaryBufferFromByteBufferFactory());
+            info = BinaryDictIOUtils.findWordByBinaryDictReader(dictReader, word);
         } catch (IOException e) {
         } catch (UnsupportedFormatException e) {
         }
@@ -172,18 +177,18 @@
     private long insertAndCheckWord(final File file, final String word, final int frequency,
             final boolean exist, final ArrayList<WeightedString> bigrams,
             final ArrayList<WeightedString> shortcuts) {
-        final BinaryDictReader reader = new BinaryDictReader(file);
+        final BinaryDictReader dictReader = new BinaryDictReader(file);
         BufferedOutputStream outStream = null;
         long amountOfTime = -1;
         try {
-            reader.openBuffer(new FusionDictionaryBufferFromWritableByteBufferFactory());
+            dictReader.openBuffer(new FusionDictionaryBufferFromWritableByteBufferFactory());
             outStream = new BufferedOutputStream(new FileOutputStream(file, true));
 
             if (!exist) {
                 assertEquals(FormatSpec.NOT_VALID_WORD, getWordPosition(file, word));
             }
             final long now = System.nanoTime();
-            DynamicBinaryDictIOUtils.insertWord(reader, outStream, word, frequency, bigrams,
+            DynamicBinaryDictIOUtils.insertWord(dictReader, outStream, word, frequency, bigrams,
                     shortcuts, false, false);
             amountOfTime = System.nanoTime() - now;
             outStream.flush();
@@ -206,24 +211,25 @@
     }
 
     private void deleteWord(final File file, final String word) {
-        final BinaryDictReader reader = new BinaryDictReader(file);
+        final BinaryDictReader dictReader = new BinaryDictReader(file);
         try {
-            reader.openBuffer(new FusionDictionaryBufferFromWritableByteBufferFactory());
-            DynamicBinaryDictIOUtils.deleteWord(reader, word);
+            dictReader.openBuffer(new FusionDictionaryBufferFromWritableByteBufferFactory());
+            DynamicBinaryDictIOUtils.deleteWord(dictReader, word);
         } catch (IOException e) {
         } catch (UnsupportedFormatException e) {
         }
     }
 
     private void checkReverseLookup(final File file, final String word, final int position) {
-        final BinaryDictReader reader = new BinaryDictReader(file);
+        final BinaryDictReader dictReader = new BinaryDictReader(file);
         try {
-            final FusionDictionaryBufferInterface buffer = reader.openAndGetBuffer(
+            final FusionDictionaryBufferInterface buffer = dictReader.openAndGetBuffer(
                     new BinaryDictReader.FusionDictionaryBufferFromByteBufferFactory());
-            final FileHeader header = BinaryDictDecoder.readHeader(buffer);
+            final FileHeader fileHeader = BinaryDictDecoder.readHeader(dictReader);
             assertEquals(word,
-                    BinaryDictDecoder.getWordAtAddress(reader.getBuffer(), header.mHeaderSize,
-                            position - header.mHeaderSize, header.mFormatOptions).mWord);
+                    BinaryDictDecoder.getWordAtAddress(dictReader.getBuffer(),
+                            fileHeader.mHeaderSize, position - fileHeader.mHeaderSize,
+                            fileHeader.mFormatOptions).mWord);
         } catch (IOException e) {
             Log.e(TAG, "Raised an IOException while looking up a word", e);
         } catch (UnsupportedFormatException e) {
@@ -234,7 +240,8 @@
     public void testInsertWord() {
         File file = null;
         try {
-            file = File.createTempFile("testInsertWord", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testInsertWord", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             fail("IOException while creating temporary file: " + e);
         }
@@ -284,7 +291,7 @@
     public void testInsertWordWithBigrams() {
         File file = null;
         try {
-            file = File.createTempFile("testInsertWordWithBigrams", ".dict",
+            file = File.createTempFile("testInsertWordWithBigrams", TEST_DICT_FILE_EXTENSION,
                     getContext().getCacheDir());
         } catch (IOException e) {
             fail("IOException while creating temporary file: " + e);
@@ -322,7 +329,8 @@
     public void testRandomWords() {
         File file = null;
         try {
-            file = File.createTempFile("testRandomWord", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testRandomWord", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
         }
         assertNotNull(file);
diff --git a/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java b/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
index c2a6264..304b792 100644
--- a/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
+++ b/tests/src/com/android/inputmethod/latin/personalization/UserHistoryDictionaryTests.java
@@ -22,6 +22,7 @@
 import android.test.suitebuilder.annotation.LargeTest;
 import android.util.Log;
 
+import com.android.inputmethod.latin.ExpandableBinaryDictionary;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 
 import java.io.File;
@@ -81,12 +82,12 @@
         }
     }
 
-    private void addAndWriteRandomWords(final String locale, final int numberOfWords,
+    private void addAndWriteRandomWords(final String testFilenameSuffix, final int numberOfWords,
             final Random random) {
         final List<String> words = generateWords(numberOfWords, random);
         final UserHistoryPredictionDictionary dict =
                 PersonalizationDictionaryHelper.getUserHistoryPredictionDictionary(getContext(),
-                        locale, mPrefs);
+                        testFilenameSuffix /* locale */, mPrefs);
         // Add random words to the user history dictionary.
         addToDict(dict, words);
         // write to file.
@@ -97,12 +98,12 @@
         File dictFile = null;
         Log.d(TAG, "This test can be used for profiling.");
         Log.d(TAG, "Usage: please set UserHistoryDictionary.PROFILE_SAVE_RESTORE to true.");
-        final String locale = "testRandomWords" + System.currentTimeMillis();
+        final String testFilenameSuffix = "testRandomWords" + System.currentTimeMillis();
         final int numberOfWords = 1000;
         final Random random = new Random(123456);
 
         try {
-            addAndWriteRandomWords(locale, numberOfWords, random);
+            addAndWriteRandomWords(testFilenameSuffix, numberOfWords, random);
         } finally {
             try {
                 Log.d(TAG, "waiting for writing ...");
@@ -111,7 +112,8 @@
                 Log.d(TAG, "InterruptedException: " + e);
             }
 
-            final String fileName = UserHistoryPredictionDictionary.NAME + "." + locale + ".dict";
+            final String fileName = UserHistoryPredictionDictionary.NAME + "." + testFilenameSuffix
+                    + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
             dictFile = new File(getContext().getFilesDir(), fileName);
 
             if (dictFile != null) {
@@ -135,8 +137,8 @@
             String testFilenameSuffixes[] = new String[numberOfLanguages];
             for (int i = 0; i < numberOfLanguages; i++) {
                 testFilenameSuffixes[i] = "testSwitchingLanguages" + i;
-                final String fileName = "UserHistoryDictionary." + testFilenameSuffixes[i]
-                        + ".dict";
+                final String fileName = UserHistoryPredictionDictionary.NAME + "." +
+                        testFilenameSuffixes[i] + ExpandableBinaryDictionary.DICT_FILE_EXTENSION;
                 dictFiles[i] = new File(getContext().getFilesDir(), fileName);
             }
 
diff --git a/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java b/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
index fd55176..8f5bec8 100644
--- a/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
+++ b/tests/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtilsTests.java
@@ -49,6 +49,7 @@
     private static final int BIGRAM_FREQUENCY = 100;
     private static final ArrayList<String> NOT_HAVE_BIGRAM = new ArrayList<String>();
     private static final FormatSpec.FormatOptions FORMAT_OPTIONS = new FormatSpec.FormatOptions(2);
+    private static final String TEST_DICT_FILE_EXTENSION = ".testDict";
 
     /**
      * Return same frequency for all words and bigrams
@@ -177,7 +178,8 @@
 
         File file = null;
         try {
-            file = File.createTempFile("testReadAndWrite", ".dict", getContext().getCacheDir());
+            file = File.createTempFile("testReadAndWrite", TEST_DICT_FILE_EXTENSION,
+                    getContext().getCacheDir());
         } catch (IOException e) {
             Log.d(TAG, "IOException while creating a temporary file", e);
         }