diff --git a/java/src/com/android/inputmethod/latin/UserHistoryDictIOUtils.java b/java/src/com/android/inputmethod/latin/UserHistoryDictIOUtils.java
new file mode 100644
index 0000000..2963e37
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/UserHistoryDictIOUtils.java
@@ -0,0 +1,193 @@
+/*
+ * Copyright (C) 2012 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;
+
+import android.util.Log;
+
+import com.android.inputmethod.latin.makedict.BinaryDictInputOutput;
+import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.FusionDictionaryBufferInterface;
+import com.android.inputmethod.latin.makedict.FusionDictionary;
+import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
+import com.android.inputmethod.latin.makedict.PendingAttribute;
+import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Reads and writes Binary files for a UserHistoryDictionary.
+ *
+ * All the methods in this class are static.
+ */
+public class UserHistoryDictIOUtils {
+    private static final String TAG = UserHistoryDictIOUtils.class.getSimpleName();
+    private static final boolean DEBUG = false;
+
+    public interface OnAddWordListener {
+        public void setUnigram(final String word, final String shortcutTarget, final int frequency);
+        public void setBigram(final String word1, final String word2, final int frequency);
+    }
+
+    public interface BigramDictionaryInterface {
+        public int getFrequency(final String word1, final String word2);
+    }
+
+    public static final class ByteArrayWrapper implements FusionDictionaryBufferInterface {
+        private byte[] mBuffer;
+        private int mPosition;
+
+        ByteArrayWrapper(final byte[] buffer) {
+            mBuffer = buffer;
+            mPosition = 0;
+        }
+
+        @Override
+        public int readUnsignedByte() {
+            return ((int)mBuffer[mPosition++]) & 0xFF;
+        }
+
+        @Override
+        public int readUnsignedShort() {
+            final int retval = readUnsignedByte();
+            return (retval << 8) + readUnsignedByte();
+        }
+
+        @Override
+        public int readUnsignedInt24() {
+            final int retval = readUnsignedShort();
+            return (retval << 8) + readUnsignedByte();
+        }
+
+        @Override
+        public int readInt() {
+            final int retval = readUnsignedShort();
+            return (retval << 16) + readUnsignedShort();
+        }
+
+        @Override
+        public int position() {
+            return mPosition;
+        }
+
+        @Override
+        public void position(int position) {
+            mPosition = position;
+        }
+    }
+
+    /**
+     * Writes dictionary to file.
+     */
+    public static void writeDictionaryBinary(final OutputStream destination,
+            final BigramDictionaryInterface dict, final UserHistoryDictionaryBigramList bigrams,
+            final int version) {
+
+        final FusionDictionary fusionDict = constructFusionDictionary(dict, bigrams);
+
+        try {
+            BinaryDictInputOutput.writeDictionaryBinary(destination, fusionDict, version);
+        } catch (IOException e) {
+            Log.e(TAG, "IO exception while writing file: " + e);
+        } catch (UnsupportedFormatException e) {
+            Log.e(TAG, "Unsupported fomat: " + e);
+        }
+    }
+
+    /**
+     * Constructs a new FusionDictionary from BigramDictionaryInterface.
+     */
+    /* packages for test */ static FusionDictionary constructFusionDictionary(
+            final BigramDictionaryInterface dict, final UserHistoryDictionaryBigramList bigrams) {
+
+        final FusionDictionary fusionDict = new FusionDictionary(new Node(),
+                new FusionDictionary.DictionaryOptions(
+                        new HashMap<String,String>(), false, false));
+
+        for (final String word1 : bigrams.keySet()) {
+            final HashMap<String, Byte> word1Bigrams = bigrams.getBigrams(word1);
+            for (final String word2 : word1Bigrams.keySet()) {
+                final int freq = dict.getFrequency(word1, word2);
+
+                if (DEBUG) {
+                    if (word1 == null) {
+                        Log.d(TAG, "add unigram: " + word2 + "," + Integer.toString(freq));
+                    } else {
+                        Log.d(TAG, "add bigram: " + word1
+                                + "," + word2 + "," + Integer.toString(freq));
+                    }
+                }
+
+                if (word1 == null) { // unigram
+                    fusionDict.add(word2, freq, null);
+                } else { // bigram
+                    fusionDict.setBigram(word1, word2, freq);
+                }
+                bigrams.updateBigram(word1, word2, (byte)freq);
+            }
+        }
+
+        return fusionDict;
+    }
+
+    /**
+     * Reads dictionary from file.
+     */
+    public static void readDictionaryBinary(final FusionDictionaryBufferInterface buffer,
+            final OnAddWordListener dict) {
+        final Map<Integer, String> unigrams = CollectionUtils.newTreeMap();
+        final Map<Integer, Integer> frequencies = CollectionUtils.newTreeMap();
+        final Map<Integer, ArrayList<PendingAttribute>> bigrams = CollectionUtils.newTreeMap();
+
+        try {
+            BinaryDictInputOutput.readUnigramsAndBigramsBinary(buffer, unigrams, frequencies,
+                    bigrams);
+            addWordsFromWordMap(unigrams, frequencies, bigrams, dict);
+        } catch (IOException e) {
+            Log.e(TAG, "IO exception while reading file: " + e);
+        } catch (UnsupportedFormatException e) {
+            Log.e(TAG, "Unsupported format: " + e);
+        }
+    }
+
+    /**
+     * Adds all unigrams and bigrams in maps to OnAddWordListener.
+     */
+    /* package for test */ static void addWordsFromWordMap(final Map<Integer, String> unigrams,
+            final Map<Integer, Integer> frequencies,
+            final Map<Integer, ArrayList<PendingAttribute>> bigrams, final OnAddWordListener to) {
+
+        for (Map.Entry<Integer, String> entry : unigrams.entrySet()) {
+            final String word1 = entry.getValue();
+            final int unigramFrequency = frequencies.get(entry.getKey());
+            to.setUnigram(word1, null, unigramFrequency);
+
+            final ArrayList<PendingAttribute> attrList = bigrams.get(entry.getKey());
+
+            if (attrList != null) {
+                for (final PendingAttribute attr : attrList) {
+                    to.setBigram(word1, unigrams.get(attr.mAddress),
+                            BinaryDictInputOutput.reconstructBigramFrequency(unigramFrequency,
+                                    attr.mFrequency));
+                }
+            }
+        }
+
+    }
+}
\ No newline at end of file
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
index 9f7f413..bb7d1b2 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
@@ -189,7 +189,7 @@
     // suspicion that a bug might be causing an infinite loop.
     private static final int MAX_PASSES = 24;
 
-    private interface FusionDictionaryBufferInterface {
+    public interface FusionDictionaryBufferInterface {
         public int readUnsignedByte();
         public int readUnsignedShort();
         public int readUnsignedInt24();
@@ -234,7 +234,6 @@
         @Override
         public void position(int newPos) {
             mBuffer.position(newPos);
-            return;
         }
     }
 
@@ -1393,7 +1392,6 @@
             final FusionDictionaryBufferInterface buffer, final int headerSize,
             final Map<Integer, String> words, final Map<Integer, Integer> frequencies,
             final Map<Integer, ArrayList<PendingAttribute>> bigrams) {
-
         int[] pushedChars = new int[MAX_WORD_LENGTH + 1];
 
         Stack<Position> stack = new Stack<Position>();
@@ -1443,8 +1441,6 @@
                 stack.push(childrenPos);
             }
         }
-
-        return;
     }
 
     /**
@@ -1462,7 +1458,6 @@
             final Map<Integer, String> words, final Map<Integer, Integer> frequencies,
             final Map<Integer, ArrayList<PendingAttribute>> bigrams) throws IOException,
             UnsupportedFormatException {
-
         // Read header
         final int version = checkFormatVersion(buffer);
         final int optionsFlags = buffer.readUnsignedShort();
@@ -1507,10 +1502,8 @@
      * @throws UnsupportedFormatException
      */
     private static int readHeader(final FusionDictionaryBufferInterface buffer,
-            final HashMap<String, String> options,
-            final int version)
+            final HashMap<String, String> options, final int version)
             throws IOException, UnsupportedFormatException {
-
         final int headerSize;
         if (version < FIRST_VERSION_WITH_HEADER_SIZE) {
             headerSize = buffer.position();
@@ -1523,7 +1516,6 @@
         if (headerSize < 0) {
             throw new UnsupportedFormatException("header size can't be negative.");
         }
-
         return headerSize;
     }
 
@@ -1561,7 +1553,6 @@
     public static FusionDictionary readDictionaryBinary(
             final FusionDictionaryBufferInterface buffer, final FusionDictionary dict)
                     throws IOException, UnsupportedFormatException {
-
         // clear cache
         wordCache.clear();
 
diff --git a/tests/src/com/android/inputmethod/latin/UserHistoryDictIOUtilsTests.java b/tests/src/com/android/inputmethod/latin/UserHistoryDictIOUtilsTests.java
new file mode 100644
index 0000000..8f0551b
--- /dev/null
+++ b/tests/src/com/android/inputmethod/latin/UserHistoryDictIOUtilsTests.java
@@ -0,0 +1,249 @@
+/*
+ * Copyright (C) 2012 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;
+
+import com.android.inputmethod.latin.UserHistoryDictIOUtils.BigramDictionaryInterface;
+import com.android.inputmethod.latin.UserHistoryDictIOUtils.OnAddWordListener;
+import com.android.inputmethod.latin.makedict.FusionDictionary;
+import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
+
+import android.content.Context;
+import android.test.AndroidTestCase;
+import android.util.Log;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+
+/**
+ * Unit tests for UserHistoryDictIOUtils
+ */
+public class UserHistoryDictIOUtilsTests extends AndroidTestCase
+    implements BigramDictionaryInterface {
+
+    private static final String TAG = UserHistoryDictIOUtilsTests.class.getSimpleName();
+    private static final int UNIGRAM_FREQUENCY = 50;
+    private static final int BIGRAM_FREQUENCY = 100;
+    private static final ArrayList<String> NOT_HAVE_BIGRAM = new ArrayList<String>();
+
+    /**
+     * Return same frequency for all words and bigrams
+     */
+    @Override
+    public int getFrequency(String word1, String word2) {
+        if (word1 == null) return UNIGRAM_FREQUENCY;
+        return BIGRAM_FREQUENCY;
+    }
+
+    // Utilities for Testing
+
+    private void addWord(final String word,
+            final HashMap<String, ArrayList<String> > addedWords) {
+        if (!addedWords.containsKey(word)) {
+            addedWords.put(word, new ArrayList<String>());
+        }
+    }
+
+    private void addBigram(final String word1, final String word2,
+            final HashMap<String, ArrayList<String> > addedWords) {
+        addWord(word1, addedWords);
+        addWord(word2, addedWords);
+        addedWords.get(word1).add(word2);
+    }
+
+    private void addBigramToBigramList(final String word1, final String word2,
+            final HashMap<String, ArrayList<String> > addedWords,
+            final UserHistoryDictionaryBigramList bigramList) {
+        bigramList.addBigram(null, word1);
+        bigramList.addBigram(word1, word2);
+
+        addBigram(word1, word2, addedWords);
+    }
+
+    private void checkWordInFusionDict(final FusionDictionary dict, final String word,
+            final ArrayList<String> expectedBigrams) {
+        final CharGroup group = FusionDictionary.findWordInTree(dict.mRoot, word);
+        assertNotNull(group);
+        assertTrue(group.isTerminal());
+
+        for (final String bigram : expectedBigrams) {
+            assertNotNull(group.getBigram(bigram));
+        }
+    }
+
+    private void checkWordsInFusionDict(final FusionDictionary dict,
+            final HashMap<String, ArrayList<String> > bigrams) {
+        for (final String word : bigrams.keySet()) {
+            if (bigrams.containsKey(word)) {
+                checkWordInFusionDict(dict, word, bigrams.get(word));
+            } else {
+                checkWordInFusionDict(dict, word, NOT_HAVE_BIGRAM);
+            }
+        }
+    }
+
+    private void checkWordInBigramList(
+            final UserHistoryDictionaryBigramList bigramList, final String word,
+            final ArrayList<String> expectedBigrams) {
+        // check unigram
+        final HashMap<String,Byte> unigramMap = bigramList.getBigrams(null);
+        assertTrue(unigramMap.containsKey(word));
+
+        // check bigrams
+        final ArrayList<String> actualBigrams = new ArrayList<String>(
+                bigramList.getBigrams(word).keySet());
+
+        Collections.sort(expectedBigrams);
+        Collections.sort(actualBigrams);
+        assertEquals(expectedBigrams, actualBigrams);
+    }
+
+    private void checkWordsInBigramList(final UserHistoryDictionaryBigramList bigramList,
+            final HashMap<String, ArrayList<String> > addedWords) {
+        for (final String word : addedWords.keySet()) {
+            if (addedWords.containsKey(word)) {
+                checkWordInBigramList(bigramList, word, addedWords.get(word));
+            } else {
+                checkWordInBigramList(bigramList, word, NOT_HAVE_BIGRAM);
+            }
+        }
+    }
+
+    private void writeDictToFile(final File file,
+            final UserHistoryDictionaryBigramList bigramList) {
+        try {
+            final FileOutputStream out = new FileOutputStream(file);
+            UserHistoryDictIOUtils.writeDictionaryBinary(out, this, bigramList, 2);
+            out.flush();
+            out.close();
+        } catch (IOException e) {
+            Log.e(TAG, "IO exception while writing file: " + e);
+        }
+    }
+
+    private void readDictFromFile(final File file, final OnAddWordListener listener) {
+        FileInputStream inStream = null;
+
+        try {
+            inStream = new FileInputStream(file);
+            final byte[] buffer = new byte[(int)file.length()];
+            inStream.read(buffer);
+
+            UserHistoryDictIOUtils.readDictionaryBinary(
+                    new UserHistoryDictIOUtils.ByteArrayWrapper(buffer), listener);
+        } catch (FileNotFoundException e) {
+            Log.e(TAG, "file not found: " + e);
+        } catch (IOException e) {
+            Log.e(TAG, "IOException: " + e);
+        } finally {
+            if (inStream != null) {
+                try {
+                    inStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
+    }
+
+    public void testGenerateFusionDictionary() {
+        final UserHistoryDictionaryBigramList originalList = new UserHistoryDictionaryBigramList();
+
+        final HashMap<String, ArrayList<String> > addedWords =
+                new HashMap<String, ArrayList<String>>();
+        addBigramToBigramList("this", "is", addedWords, originalList);
+        addBigramToBigramList("this", "was", addedWords, originalList);
+        addBigramToBigramList("hello", "world", addedWords, originalList);
+
+        final FusionDictionary fusionDict =
+                UserHistoryDictIOUtils.constructFusionDictionary(this, originalList);
+
+        checkWordsInFusionDict(fusionDict, addedWords);
+    }
+
+    public void testReadAndWrite() {
+        final Context context = getContext();
+
+        File file = null;
+        try {
+            file = File.createTempFile("testReadAndWrite", ".dict");
+        } catch (IOException e) {
+            Log.d(TAG, "IOException while creating a temporary file: " + e);
+        }
+        assertNotNull(file);
+
+        // make original dictionary
+        final UserHistoryDictionaryBigramList originalList = new UserHistoryDictionaryBigramList();
+        final HashMap<String, ArrayList<String>> addedWords = CollectionUtils.newHashMap();
+        addBigramToBigramList("this" , "is"   , addedWords, originalList);
+        addBigramToBigramList("this" , "was"  , addedWords, originalList);
+        addBigramToBigramList("is"   , "not"  , addedWords, originalList);
+        addBigramToBigramList("hello", "world", addedWords, originalList);
+
+        // write to file
+        writeDictToFile(file, originalList);
+
+        // make result dict.
+        final UserHistoryDictionaryBigramList resultList = new UserHistoryDictionaryBigramList();
+        final OnAddWordListener listener = new OnAddWordListener() {
+            @Override
+            public void setUnigram(final String word,
+                    final String shortcutTarget, final int frequency) {
+                Log.d(TAG, "in: setUnigram: " + word + "," + frequency);
+                resultList.addBigram(null, word, (byte)frequency);
+            }
+            @Override
+            public void setBigram(final String word1, final String word2, final int frequency) {
+                Log.d(TAG, "in: setBigram: " + word1 + "," + word2 + "," + frequency);
+                resultList.addBigram(word1, word2, (byte)frequency);
+            }
+        };
+
+        // load from file
+        readDictFromFile(file, listener);
+        checkWordsInBigramList(resultList, addedWords);
+
+        // add new bigram
+        addBigramToBigramList("hello", "java", addedWords, resultList);
+
+        // rewrite
+        writeDictToFile(file, resultList);
+        final UserHistoryDictionaryBigramList resultList2 = new UserHistoryDictionaryBigramList();
+        final OnAddWordListener listener2 = new OnAddWordListener() {
+            @Override
+            public void setUnigram(final String word,
+                    final String shortcutTarget, final int frequency) {
+                Log.d(TAG, "in: setUnigram: " + word + "," + frequency);
+                resultList2.addBigram(null, word, (byte)frequency);
+            }
+            @Override
+            public void setBigram(final String word1, final String word2, final int frequency) {
+                Log.d(TAG, "in: setBigram: " + word1 + "," + word2 + "," + frequency);
+                resultList2.addBigram(word1, word2, (byte)frequency);
+            }
+        };
+
+        // load from file
+        readDictFromFile(file, listener2);
+        checkWordsInBigramList(resultList2, addedWords);
+    }
+}