[FlexBuffers][Java] Implementation of FlexBuffers API (#5476)

* [FlexBuffers][Java] Implementation of FlexBuffers API

This is the initial attemp to implement FlexBuffer on Java.

There is some limitations as compared to the C++ implementation:
  1 - No mutations implemented yet
  2 - Does not parse from json

Also, this initial implementation is not focused and performance, but
get the basics write. So there is many opportunities for optimization, for instance,
remove all enums, return CharSequence instead of Strings and object pooling.

* [FlexBuffers][Java] Optimizations and simplification of the Builder  API.

This change removes BitWidth enum in favor of static ints. Also
make all "reads" APIs closer to C++ implementation (try to cast or convert
as much as possible, assuming user knows what he is doing). Finally,
we remove the helper classes for building vectors and maps.

There is no official benchmarks, but the unit tests are running in less
than 50% for previous runs, which mean those optimizations are worth it.

* [FlexBuffers][Java] Fix Reference::asString behavior

There was a incorrect assumption that strings would be null-terminated, which
could lead to truncated strings. S now it relies size instead of null-termination.

Other minor improvements

2 files changed, 1561 insertions, 0 deletions

diff --git a/java/com/google/flatbuffers/FlexBuffers.java b/java/com/google/flatbuffers/FlexBuffers.java
new file mode 100644
index 00000000..07e162d9
--- /dev/null
+++ b/java/com/google/flatbuffers/FlexBuffers.java
@@ -0,0 +1,869 @@
+/*
+ * Copyright 2014 Google Inc. All rights reserved.
+ *
+ * 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.google.flatbuffers;
+
+
+import static com.google.flatbuffers.FlexBuffers.Unsigned.byteToUnsignedInt;
+import static com.google.flatbuffers.FlexBuffers.Unsigned.intToUnsignedLong;
+import static com.google.flatbuffers.FlexBuffers.Unsigned.shortToUnsignedInt;
+
+import java.math.BigInteger;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * This class can be used to parse FlexBuffer messages.
+ * <p>
+ * For generating FlexBuffer messages, use {@link FlexBuffersBuilder}.
+ * <p>
+ * Example of usage:
+ * ByteBuffer bb = ... // load message from file or network
+ * FlexBuffers.Reference r = FlexBuffers.getRoot(bb); // Reads the root element
+ * FlexBuffers.Map map = r.asMap(); // We assumed root object is a map
+ * System.out.println(map.get("name").asString()); // prints element with key "name"
+ */
+public class FlexBuffers {
+
+    // These are used as the upper 6 bits of a type field to indicate the actual
+    // type.
+    public static final int FBT_NULL = 0;
+    public static final int FBT_INT = 1;
+    public static final int FBT_UINT = 2;
+    public static final int FBT_FLOAT = 3; // Types above stored inline, types below store an offset.
+    public static final int FBT_KEY = 4;
+    public static final int FBT_STRING = 5;
+    public static final int FBT_INDIRECT_INT = 6;
+    public static final int FBT_INDIRECT_UINT = 7;
+    public static final int FBT_INDIRECT_FLOAT = 8;
+    public static final int FBT_MAP = 9;
+    public static final int FBT_VECTOR = 10; // Untyped.
+    public static final int FBT_VECTOR_INT = 11;  // Typed any size  = stores no type table).
+    public static final int FBT_VECTOR_UINT = 12;
+    public static final int FBT_VECTOR_FLOAT = 13;
+    public static final int FBT_VECTOR_KEY = 14;
+    public static final int FBT_VECTOR_STRING = 15;
+    public static final int FBT_VECTOR_INT2 = 16;  // Typed tuple  = no type table; no size field).
+    public static final int FBT_VECTOR_UINT2 = 17;
+    public static final int FBT_VECTOR_FLOAT2 = 18;
+    public static final int FBT_VECTOR_INT3 = 19;  // Typed triple  = no type table; no size field).
+    public static final int FBT_VECTOR_UINT3 = 20;
+    public static final int FBT_VECTOR_FLOAT3 = 21;
+    public static final int FBT_VECTOR_INT4 = 22;  // Typed quad  = no type table; no size field).
+    public static final int FBT_VECTOR_UINT4 = 23;
+    public static final int FBT_VECTOR_FLOAT4 = 24;
+    public static final int FBT_BLOB = 25;
+    public static final int FBT_BOOL = 26;
+    public static final int FBT_VECTOR_BOOL = 36;  // To Allow the same type of conversion of type to vector type
+    private static final ByteBuffer EMPTY_BB = ByteBuffer.allocate(0).asReadOnlyBuffer();
+
+    /**
+     * Checks where a type is a typed vector
+     *
+     * @param type type to be checked
+     * @return true if typed vector
+     */
+    static boolean isTypedVector(int type) {
+        return (type >= FBT_VECTOR_INT && type <= FBT_VECTOR_STRING) || type == FBT_VECTOR_BOOL;
+    }
+
+    /**
+     * Check whether you can access type directly (no indirection) or not.
+     *
+     * @param type type to be checked
+     * @return true if inline type
+     */
+    static boolean isTypeInline(int type) {
+        return type <= FBT_FLOAT || type == FBT_BOOL;
+    }
+
+    static int toTypedVectorElementType(int original_type) {
+        return original_type - FBT_VECTOR_INT + FBT_INT;
+    }
+
+    /**
+     * Return a vector type our of a original element type
+     *
+     * @param type        element type
+     * @param fixedLength size of elment
+     * @return typed vector type
+     */
+    static int toTypedVector(int type, int fixedLength) {
+        assert (isTypedVectorElementType(type));
+        switch (fixedLength) {
+            case 0: return type - FBT_INT + FBT_VECTOR_INT;
+            case 2: return type - FBT_INT + FBT_VECTOR_INT2;
+            case 3: return type - FBT_INT + FBT_VECTOR_INT3;
+            case 4: return type - FBT_INT + FBT_VECTOR_INT4;
+            default:
+                assert (false);
+                return FBT_NULL;
+        }
+    }
+
+    static boolean isTypedVectorElementType(int type) {
+        return (type >= FBT_INT && type <= FBT_STRING) || type == FBT_BOOL;
+    }
+
+    // return position of the element that the offset is pointing to
+    private static int indirect(ByteBuffer bb, int offset, int byteWidth) {
+        //TODO: we assume all offset fits on a int, since ByteBuffer operates with that assumption
+        return (int) (offset - readUInt(bb, offset, byteWidth));
+    }
+
+    // read unsigned int with size byteWidth and return as a 64-bit integer
+    private static long readUInt(ByteBuffer buff, int end, int byteWidth) {
+        switch (byteWidth) {
+            case 1: return byteToUnsignedInt(buff.get(end));
+            case 2: return shortToUnsignedInt(buff.getShort(end));
+            case 4: return intToUnsignedLong(buff.getInt(end));
+            case 8: return buff.getLong(end); // We are passing signed long here. Losing information (user should know)
+            default: return -1; // we should never reach here
+        }
+    }
+
+    // read signed int of size byteWidth and return as 32-bit int
+    private static int readInt(ByteBuffer buff, int end, int byteWidth) {
+        return (int) readLong(buff, end, byteWidth);
+    }
+
+    // read signed int of size byteWidth and return as 64-bit int
+    private static long readLong(ByteBuffer buff, int end, int byteWidth) {
+        switch (byteWidth) {
+            case 1: return buff.get(end);
+            case 2: return buff.getShort(end);
+            case 4: return buff.getInt(end);
+            case 8: return buff.getLong(end);
+            default: return -1; // we should never reach here
+        }
+    }
+
+    private static double readDouble(ByteBuffer buff, int end, int byteWidth) {
+        switch (byteWidth) {
+            case 4: return buff.getFloat(end);
+            case 8: return buff.getDouble(end);
+            default: return -1; // we should never reach here
+        }
+    }
+
+    /**
+     * Reads a FlexBuffer message in ByteBuffer and returns {@link Reference} to
+     * the root element.
+     * @param buffer ByteBuffer containing FlexBuffer message
+     * @return {@link Reference} to the root object
+     */
+    public static Reference getRoot(ByteBuffer buffer) {
+        // See Finish() below for the serialization counterpart of this.
+        // The root ends at the end of the buffer, so we parse backwards from there.
+        int end = buffer.limit();
+        int byteWidth = buffer.get(--end);
+        int packetType = byteToUnsignedInt(buffer.get(--end));
+        end -= byteWidth;  // The root data item.
+        return new Reference(buffer, end, byteWidth, packetType);
+    }
+
+    public static class Reference {
+
+        private static final Reference NULL_REFERENCE = new Reference(EMPTY_BB, 0, 1, 0);
+        private ByteBuffer bb;
+        private int end;
+        private int parentWidth;
+        private int byteWidth;
+        private int type;
+
+        Reference(ByteBuffer bb, int end, int parentWidth, int packedType) {
+            this(bb, end, parentWidth, (1 << (packedType & 3)), packedType >> 2);
+        }
+
+        Reference(ByteBuffer bb, int end, int parentWidth, int byteWidth, int type) {
+            this.bb = bb;
+            this.end = end;
+            this.parentWidth = parentWidth;
+            this.byteWidth = byteWidth;
+            this.type = type;
+        }
+
+        public int getType() {
+            return type;
+        }
+
+        public boolean isNull() {
+            return type == FBT_NULL;
+        }
+
+        public boolean isBoolean() {
+            return type == FBT_BOOL;
+        }
+
+        public boolean isNumeric() {
+            return isIntOrUInt() || isFloat();
+        }
+
+        public boolean isIntOrUInt() {
+            return isInt() || isUInt();
+        }
+
+        public boolean isFloat() {
+            return type == FBT_FLOAT || type == FBT_INDIRECT_FLOAT;
+        }
+
+        public boolean isInt() {
+            return type == FBT_INT || type == FBT_INDIRECT_INT;
+        }
+
+        public boolean isUInt() {
+            return type == FBT_UINT || type == FBT_INDIRECT_UINT;
+        }
+
+        public boolean isString() {
+            return type == FBT_STRING;
+        }
+
+        public boolean isKey() {
+            return type == FBT_KEY;
+        }
+
+        public boolean isVector() {
+            return type == FBT_VECTOR || type == FBT_MAP;
+        }
+
+        public boolean isTypedVector() {
+            return (type >= FBT_VECTOR_INT && type <= FBT_VECTOR_STRING) ||
+                    type == FBT_VECTOR_BOOL;
+        }
+
+        public boolean isMap() {
+            return type == FBT_MAP;
+        }
+
+        public boolean isBlob() {
+            return type == FBT_BLOB;
+        }
+
+        public int asInt() {
+            if (type == FBT_INT) {
+                // A fast path for the common case.
+                return readInt(bb, end, parentWidth);
+            } else
+                switch (type) {
+                    case FBT_INDIRECT_INT: return readInt(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_UINT: return (int) readUInt(bb, end, parentWidth);
+                    case FBT_INDIRECT_UINT: return (int) readUInt(bb, indirect(bb, end, parentWidth), parentWidth);
+                    case FBT_FLOAT: return (int) readDouble(bb, end, parentWidth);
+                    case FBT_INDIRECT_FLOAT: return (int) readDouble(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_NULL: return 0;
+                    case FBT_STRING: return Integer.parseInt(asString());
+                    case FBT_VECTOR: return asVector().size();
+                    case FBT_BOOL: return readInt(bb, end, parentWidth);
+                    default:
+                        // Convert other things to int.
+                        return 0;
+                }
+        }
+
+        public long asUInt() {
+            if (type == FBT_UINT) {
+                // A fast path for the common case.
+                return readUInt(bb, end, parentWidth);
+            } else
+                switch (type) {
+                    case FBT_INDIRECT_UINT: return readUInt(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_INT: return readLong(bb, end, parentWidth);
+                    case FBT_INDIRECT_INT: return readLong(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_FLOAT: return (long) readDouble(bb, end, parentWidth);
+                    case FBT_INDIRECT_FLOAT: return (long) readDouble(bb,  indirect(bb, end, parentWidth), parentWidth);
+                    case FBT_NULL: return 0;
+                    case FBT_STRING: return Long.parseLong(asString());
+                    case FBT_VECTOR: return asVector().size();
+                    case FBT_BOOL: readInt(bb, end, parentWidth);
+                    default:
+                        // Convert other things to uint.
+                        return 0;
+                }
+        }
+
+        public long asLong() {
+            if (type == FBT_INT) {
+                // A fast path for the common case.
+                return readLong(bb, end, parentWidth);
+            } else
+                switch (type) {
+                    case FBT_INDIRECT_INT: return readLong(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_UINT: return readUInt(bb, end, parentWidth);
+                    case FBT_INDIRECT_UINT: return readUInt(bb, indirect(bb, end, parentWidth), parentWidth);
+                    case FBT_FLOAT: return (long) readDouble(bb, end, parentWidth);
+                    case FBT_INDIRECT_FLOAT: return (long) readDouble(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_NULL: return 0;
+                    case FBT_STRING: {
+                        try {
+                            return Long.parseLong(asString());
+                        } catch (NumberFormatException nfe) {
+                            return 0; //same as C++ implementation
+                        }
+                    }
+                    case FBT_VECTOR: return asVector().size();
+                    case FBT_BOOL: return readInt(bb, end, parentWidth);
+                    default:
+                        // Convert other things to int.
+                        return 0;
+                }
+        }
+
+        public double asFloat() {
+            if (type == FBT_FLOAT) {
+                // A fast path for the common case.
+                return readDouble(bb, end, parentWidth);
+            } else
+                switch (type) {
+                    case FBT_INDIRECT_FLOAT: return readDouble(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_INT: return readInt(bb, end, parentWidth);
+                    case FBT_UINT:
+                    case FBT_BOOL:
+                        return readUInt(bb, end, parentWidth);
+                    case FBT_INDIRECT_INT: return readInt(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_INDIRECT_UINT: return readUInt(bb, indirect(bb, end, parentWidth), byteWidth);
+                    case FBT_NULL: return 0.0;
+                    case FBT_STRING: return Double.parseDouble(asString());
+                    case FBT_VECTOR: return asVector().size();
+                    default:
+                        // Convert strings and other things to float.
+                        return 0;
+                }
+        }
+
+        public Key asKey() {
+            if (isKey()) {
+                return new Key(bb, indirect(bb, end, parentWidth), byteWidth);
+            } else {
+                return Key.empty();
+            }
+        }
+
+        public String asString() {
+            if (isString()) {
+                int start = indirect(bb, end, byteWidth);
+                int size = readInt(bb, start - byteWidth, byteWidth);
+                return Utf8.getDefault().decodeUtf8(bb, start, size);
+            }
+            else if (isKey()){
+                int start = indirect(bb, end, byteWidth);
+                for (int i = start; ; i++) {
+                    if (bb.get(i) == 0) {
+                        return Utf8.getDefault().decodeUtf8(bb, start, i - start);
+                    }
+                }
+            } else {
+                return "";
+            }
+        }
+
+        public Map asMap() {
+            if (isMap()) {
+                return new Map(bb, indirect(bb, end, parentWidth), byteWidth);
+            } else {
+                return Map.empty();
+            }
+        }
+
+        public Vector asVector() {
+            if (isVector()) {
+                return new Vector(bb, indirect(bb, end, parentWidth), byteWidth);
+            } else if (FlexBuffers.isTypedVector(type)) {
+                return new TypedVector(bb, indirect(bb, end, parentWidth), byteWidth, FlexBuffers.toTypedVectorElementType(type));
+            } else {
+                return Vector.empty();
+            }
+        }
+
+        public Blob asBlob() {
+            if (isBlob() || isString()) {
+                return new Blob(bb, indirect(bb, end, parentWidth), byteWidth);
+            } else {
+                return Blob.empty();
+            }
+        }
+
+        public boolean asBoolean() {
+            if (isBoolean()) {
+                return bb.get(end) != 0;
+            }
+            return asUInt() != 0;
+        }
+
+        @Override
+        public String toString() {
+            return toString(new StringBuilder(128)).toString();
+        }
+
+        StringBuilder toString(StringBuilder sb) {
+            //TODO: Original C++ implementation escape strings.
+            // probably we should do it as well.
+            switch (type) {
+                case FBT_NULL:
+                    return sb.append("null");
+                case FBT_INT:
+                case FBT_INDIRECT_INT:
+                    return sb.append(asLong());
+                case FBT_UINT:
+                case FBT_INDIRECT_UINT:
+                    return sb.append(asUInt());
+                case FBT_INDIRECT_FLOAT:
+                case FBT_FLOAT:
+                    return sb.append(asFloat());
+                case FBT_KEY:
+                    return asKey().toString(sb.append('"')).append('"');
+                case FBT_STRING:
+                    return sb.append('"').append(asString()).append('"');
+                case FBT_MAP:
+                    return asMap().toString(sb);
+                case FBT_VECTOR:
+                    return asVector().toString(sb);
+                case FBT_BLOB:
+                    return asBlob().toString(sb);
+                case FBT_BOOL:
+                    return sb.append(asBoolean());
+                case FBT_VECTOR_INT:
+                case FBT_VECTOR_UINT:
+                case FBT_VECTOR_FLOAT:
+                case FBT_VECTOR_KEY:
+                case FBT_VECTOR_STRING:
+                case FBT_VECTOR_BOOL:
+                    return sb.append(asVector());
+                case FBT_VECTOR_INT2:
+                case FBT_VECTOR_UINT2:
+                case FBT_VECTOR_FLOAT2:
+                case FBT_VECTOR_INT3:
+                case FBT_VECTOR_UINT3:
+                case FBT_VECTOR_FLOAT3:
+                case FBT_VECTOR_INT4:
+                case FBT_VECTOR_UINT4:
+                case FBT_VECTOR_FLOAT4:
+
+                    throw new FlexBufferException("not_implemented:" + type);
+                default:
+                    return sb;
+            }
+        }
+    }
+
+    /**
+     * Base class of all types below.
+     * Points into the data buffer and allows access to one type.
+     */
+    private static abstract class Object {
+        ByteBuffer bb;
+        int end;
+        int byteWidth;
+
+        Object(ByteBuffer buff, int end, int byteWidth) {
+            this.bb = buff;
+            this.end = end;
+            this.byteWidth = byteWidth;
+        }
+
+        @Override
+        public String toString() {
+            return toString(new StringBuilder(128)).toString();
+        }
+
+        public abstract StringBuilder toString(StringBuilder sb);
+    }
+
+    // Stores size in `byte_width_` bytes before end position.
+    private static abstract class Sized extends Object {
+        Sized(ByteBuffer buff, int end, int byteWidth) {
+            super(buff, end, byteWidth);
+        }
+
+        public int size() {
+            return readInt(bb, end - byteWidth, byteWidth);
+        }
+    }
+
+    public static class Blob extends Sized {
+        static final Blob EMPTY = new Blob(EMPTY_BB, 0, 1);
+
+        Blob(ByteBuffer buff, int end, int byteWidth) {
+            super(buff, end, byteWidth);
+        }
+
+        public static Blob empty() {
+            return EMPTY;
+        }
+
+        /**
+         * @return blob as a {@link ByteBuffer}
+         */
+        public ByteBuffer data() {
+            ByteBuffer dup = bb.duplicate();
+            dup.position(end);
+            dup.limit(end + size());
+            return dup.asReadOnlyBuffer().slice();
+        }
+
+        /**
+         * @return blob as a byte array
+         */
+        public byte[] getBytes() {
+            int size = size();
+            byte[] result = new byte[size];
+            for (int i = 0; i < size; i++) {
+                result[i] = bb.get(end + i);
+            }
+            return result;
+        }
+
+        public byte get(int pos) {
+            assert pos >=0 && pos <= size();
+            return bb.get(end + pos);
+        }
+
+        @Override
+        public String toString() {
+            return Utf8.getDefault().decodeUtf8(bb, end, size());
+        }
+
+        @Override
+        public StringBuilder toString(StringBuilder sb) {
+            sb.append('"');
+            sb.append(Utf8.getDefault().decodeUtf8(bb, end, size()));
+            return sb.append('"');
+        }
+    }
+
+    public static class Key extends Object {
+
+        private static final Key EMPTY = new Key(EMPTY_BB, 0, 0);
+
+        Key(ByteBuffer buff, int end, int byteWidth) {
+            super(buff, end, byteWidth);
+        }
+
+        public static Key empty() {
+            return Key.EMPTY;
+        }
+
+        @Override
+        public StringBuilder toString(StringBuilder sb) {
+            int size;
+            for (int i = end; ; i++) {
+                if (bb.get(i) == 0) {
+                    size = i - end;
+                    break;
+                }
+            }
+            sb.append(Utf8.getDefault().decodeUtf8(bb, end, size));
+            return sb;
+        }
+
+        int compareTo(byte[] other) {
+            int ia = end;
+            int io = 0;
+            byte c1, c2;
+            do {
+                c1 = bb.get(ia);
+                c2 = other[io];
+                if (c1 == '\0')
+                    return c1 - c2;
+                ia++;
+                io++;
+                if (io == other.length) {
+                    // in our buffer we have an additional \0 byte
+                    // but this does not exist in regular Java strings, so we return now
+                    return c1 - c2;
+                }
+            }
+            while (c1 == c2);
+            return c1 - c2;
+        }
+
+        @Override
+        public boolean equals(java.lang.Object obj) {
+            if (!(obj instanceof Key))
+                return false;
+
+            return ((Key) obj).end == end && ((Key) obj).byteWidth == byteWidth;
+        }
+    }
+
+    /**
+     * Map object representing a set of key-value pairs.
+     */
+    public static class Map extends Vector {
+        private static final Map EMPTY_MAP = new Map(EMPTY_BB, 0, 0);
+
+        Map(ByteBuffer bb, int end, int byteWidth) {
+            super(bb, end, byteWidth);
+        }
+
+        public static Map empty() {
+            return EMPTY_MAP;
+        }
+
+        /**
+         * @param key access key to element on map
+         * @return reference to value in map
+         */
+        public Reference get(String key) {
+            return get(key.getBytes(StandardCharsets.UTF_8));
+        }
+
+        /**
+         * @param key access key to element on map. Keys are assumed to be encoded in UTF-8
+         * @return reference to value in map
+         */
+        public Reference get(byte[] key) {
+            KeyVector keys = keys();
+            int size = keys.size();
+            int index = binarySearch(keys, key);
+            if (index >= 0 && index < size) {
+                return get(index);
+            }
+            return Reference.NULL_REFERENCE;
+        }
+
+        /**
+         * Get a vector or keys in the map
+         *
+         * @return vector of keys
+         */
+        public KeyVector keys() {
+            final int num_prefixed_fields = 3;
+            int keysOffset = end - (byteWidth * num_prefixed_fields);
+            return new KeyVector(new TypedVector(bb,
+                    indirect(bb, keysOffset, byteWidth),
+                    readInt(bb, keysOffset + byteWidth, byteWidth),
+                    FBT_KEY));
+        }
+
+        /**
+         * @return {@code Vector} of values from map
+         */
+        public Vector values() {
+            return new Vector(bb, end, byteWidth);
+        }
+
+        /**
+         * Writes text (json) representation of map in a {@code StringBuilder}.
+         *
+         * @param builder {@code StringBuilder} to be appended to
+         * @return Same {@code StringBuilder} with appended text
+         */
+        public StringBuilder toString(StringBuilder builder) {
+            builder.append("{ ");
+            KeyVector keys = keys();
+            int size = size();
+            Vector vals = values();
+            for (int i = 0; i < size; i++) {
+                builder.append('"')
+                        .append(keys.get(i).toString())
+                        .append("\" : ");
+                builder.append(vals.get(i).toString());
+                if (i != size - 1)
+                    builder.append(", ");
+            }
+            builder.append(" }");
+            return builder;
+        }
+
+        // Performs a binary search on a key vector and return index of the key in key vector
+        private int binarySearch(KeyVector keys, byte[] searchedKey) {
+            int low = 0;
+            int high = keys.size() - 1;
+
+            while (low <= high) {
+                int mid = (low + high) >>> 1;
+                Key k = keys.get(mid);
+                int cmp = k.compareTo(searchedKey);
+                if (cmp < 0)
+                    low = mid + 1;
+                else if (cmp > 0)
+                    high = mid - 1;
+                else
+                    return mid; // key found
+            }
+            return -(low + 1);  // key not found
+        }
+    }
+
+    /**
+     * Object that represents a set of elements in the buffer
+     */
+    public static class Vector extends Sized {
+
+        private static final Vector EMPTY_VECTOR = new Vector(ByteBuffer.allocate(0), 1, 1);
+
+        Vector(ByteBuffer bb, int end, int byteWidth) {
+            super(bb, end, byteWidth);
+        }
+
+        public static Vector empty() {
+            return EMPTY_VECTOR;
+        }
+
+        public boolean isEmpty() {
+            return this == EMPTY_VECTOR;
+        }
+
+        @Override
+        public StringBuilder toString(StringBuilder sb) {
+            sb.append("[ ");
+            int size = size();
+            for (int i = 0; i < size; i++) {
+                get(i).toString(sb);
+                if (i != size - 1) {
+                    sb.append(", ");
+                }
+            }
+            sb.append(" ]");
+            return sb;
+        }
+
+        /**
+         * Get a element in a vector by index
+         *
+         * @param index position of the element
+         * @return {@code Reference} to the element
+         */
+        public Reference get(int index) {
+            long len = size();
+            if (index >= len) {
+                return Reference.NULL_REFERENCE;
+            }
+            int packedType = byteToUnsignedInt(bb.get((int) (end + (len * byteWidth) + index)));
+            int obj_end = end + index * byteWidth;
+            return new Reference(bb, obj_end, byteWidth, packedType);
+        }
+    }
+
+    /**
+     * Object that represents a set of elements with the same type
+     */
+    public static class TypedVector extends Vector {
+
+        private static final TypedVector EMPTY_VECTOR = new TypedVector(EMPTY_BB, 0, 1, FBT_INT);
+
+        private final int elemType;
+
+        TypedVector(ByteBuffer bb, int end, int byteWidth, int elemType) {
+            super(bb, end, byteWidth);
+            this.elemType = elemType;
+        }
+
+        public static TypedVector empty() {
+            return EMPTY_VECTOR;
+        }
+
+        /**
+         * Returns whether the vector is empty
+         *
+         * @return true if empty
+         */
+        public boolean isEmptyVector() {
+            return this == EMPTY_VECTOR;
+        }
+
+        /**
+         * Return element type for all elements in the vector
+         *
+         * @return element type
+         */
+        public int getElemType() {
+            return elemType;
+        }
+
+        /**
+         * Get reference to an object in the {@code Vector}
+         *
+         * @param pos position of the object in {@code Vector}
+         * @return reference to element
+         */
+        @Override
+        public Reference get(int pos) {
+            int len = size();
+            if (pos >= len) return Reference.NULL_REFERENCE;
+            int childPos = end + pos * byteWidth;
+            return new Reference(bb, childPos, byteWidth, 1, elemType);
+        }
+    }
+
+    /**
+     * Represent a vector of keys in a map
+     */
+    public static class KeyVector {
+
+        private final TypedVector vec;
+
+        KeyVector(TypedVector vec) {
+            this.vec = vec;
+        }
+
+        /**
+         * Return key
+         *
+         * @param pos position of the key in key vector
+         * @return key
+         */
+        public Key get(int pos) {
+            int len = size();
+            if (pos >= len) return Key.EMPTY;
+            int childPos = vec.end + pos * vec.byteWidth;
+            return new Key(vec.bb, indirect(vec.bb, childPos, vec.byteWidth), 1);
+        }
+
+        /**
+         * Returns size of key vector
+         *
+         * @return size
+         */
+        public int size() {
+            return vec.size();
+        }
+
+        public String toString() {
+            StringBuilder b = new StringBuilder();
+            b.append('[');
+            for (int i = 0; i < vec.size(); i++) {
+                vec.get(i).toString(b);
+                if (i != vec.size() - 1) {
+                    b.append(", ");
+                }
+            }
+            return b.append("]").toString();
+        }
+    }
+
+    public static class FlexBufferException extends RuntimeException {
+        FlexBufferException(String msg) {
+            super(msg);
+        }
+    }
+
+    static class Unsigned {
+
+        static int byteToUnsignedInt(byte x) {
+            return ((int) x) & 0xff;
+        }
+
+        static int shortToUnsignedInt(short x) {
+            return ((int) x) & 0xffff;
+        }
+
+        static long intToUnsignedLong(int x) {
+            return ((long) x) & 0xffffffffL;
+        }
+    }
+}
diff --git a/java/com/google/flatbuffers/FlexBuffersBuilder.java b/java/com/google/flatbuffers/FlexBuffersBuilder.java
new file mode 100644
index 00000000..36e8544a
--- /dev/null
+++ b/java/com/google/flatbuffers/FlexBuffersBuilder.java
@@ -0,0 +1,692 @@
+/*
+ * Copyright 2014 Google Inc. All rights reserved.
+ *
+ * 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.google.flatbuffers;
+
+import java.math.BigInteger;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashMap;
+
+import static com.google.flatbuffers.FlexBuffers.*;
+import static com.google.flatbuffers.FlexBuffers.Unsigned.byteToUnsignedInt;
+import static com.google.flatbuffers.FlexBuffers.Unsigned.intToUnsignedLong;
+import static com.google.flatbuffers.FlexBuffers.Unsigned.shortToUnsignedInt;
+
+/**
+ * A class that generates FlexBuffers
+ * <p>
+ * This class presents all necessary APIs to create FlexBuffers. The {@link ByteBuffer } buffer used to store the
+ * data can be created internally, or passed down in the constructor.
+ * <p>
+ * Because it uses {@link ByteBuffer} internally, this impose some limitations in generating FlexBuffers. Mostly noted,
+ * the maximum size limitation on FlexBuffer message, which is {@link Integer#MAX_VALUE}.
+ *
+ * <p>There is also some differences from the original implementation in C++. It can changed in future updates.
+ * <ul>
+ *
+ *   <li><p>No support for mutations (might change in the future).</p></li>
+ *
+ *   <li><p>Size of message limited to {@link Integer#MAX_VALUE}</p></li>
+ *
+ *   <li><p>Since Java does not support unsigned type, all unsigned operations accepts a immediate higher representation
+ *   of similar type. Unsigned long is not supported</p></li>
+ * </ul>
+ * </p>
+ */
+public class FlexBuffersBuilder {
+
+    private static final int WIDTH_8 = 0;
+    private static final int WIDTH_16 = 1;
+    private static final int WIDTH_32 = 2;
+    private static final int WIDTH_64 = 3;
+
+    /**
+     * No keys or strings will be shared
+     */
+    public static final int BUILDER_FLAG_NONE = 0;
+    /**
+     * Keys will be shared between elements. Identical keys will only be serialized once, thus possibly saving space.
+     * But serialization performance might be slower and consumes more memory.
+     */
+    public static final int BUILDER_FLAG_SHARE_KEYS = 1;
+    /**
+     * Strings will be shared between elements. Identical strings will only be serialized once, thus possibly saving space.
+     * But serialization performance might be slower and consumes more memory. This is ideal if you expect many repeated
+     * strings on the message.
+     */
+    public static final int BUILDER_FLAG_SHARE_STRINGS = 1;
+    /**
+     * Strings and keys will be shared between elements.
+     */
+    public static final int BUILDER_FLAG_SHARE_KEYS_AND_STRINGS = 3;
+    /**
+     * Reserved for the future.
+     */
+    public static final int BUILDER_FLAG_SHARE_KEY_VECTORS = 4;
+    /**
+     * Reserved for the future.
+     */
+    public static final int BUILDER_FLAG_SHARE_ALL = 7;
+
+    private final ByteBuffer bb;
+    private final ArrayList<Value> stack = new ArrayList<>();
+    private final HashMap<String, Integer> keyPool = new HashMap<>();
+    private final HashMap<String, Integer> stringPool = new HashMap<>();
+    private final int flags;
+    private boolean finished = false;
+
+    private Comparator<Value> valueComparator = new Comparator<Value>() {
+        @Override
+        public int compare(Value o1, Value o2) {
+            int ia = o1.key;
+            int io =  o2.key;
+            byte c1, c2;
+            do {
+                c1 = bb.get(ia);
+                c2 = bb.get(io);
+                if (c1 == 0)
+                    return c1 - c2;
+                ia++;
+                io++;
+            }
+            while (c1 == c2);
+            return c1 - c2;
+        }
+    };
+
+    /**
+     * Constructs a newly allocated {@code FlexBuffersBuilder} with {@link #BUILDER_FLAG_SHARE_KEYS} set.
+     */
+    public FlexBuffersBuilder() {
+        this(ByteBuffer.allocate(256), BUILDER_FLAG_SHARE_KEYS);
+    }
+
+    /**
+     * Constructs a newly allocated {@code FlexBuffersBuilder}.
+     *
+     * @param bb    ByteBuffer that will hold the message
+     * @param flags Share flags
+     */
+    public FlexBuffersBuilder(ByteBuffer bb, int flags) {
+        this.bb = bb;
+        this.flags = flags;
+        bb.order(ByteOrder.LITTLE_ENDIAN);
+        bb.position(0);
+    }
+
+    /**
+     * Constructs a newly allocated {@code FlexBuffersBuilder}.
+     *
+     * @param bb ByteBuffer that will hold the message
+     */
+    public FlexBuffersBuilder(ByteBuffer bb) {
+        this(bb, BUILDER_FLAG_SHARE_KEYS);
+    }
+
+    /**
+     * Return {@code ByteBuffer} containing FlexBuffer message. {@code #finish()} must be called before calling this
+     * function otherwise an assert will trigger.
+     *
+     * @return {@code ByteBuffer} with finished message
+     */
+    public ByteBuffer getBuffer() {
+        assert (finished);
+        return bb;
+    }
+
+    /**
+     * Insert a single boolean into the buffer
+     * @param val true or false
+     */
+    public void putBoolean(boolean val) {
+        putBoolean(null, val);
+    }
+
+    public void putBoolean(String key, boolean val) {
+        stack.add(Value.bool(putKey(key), val));
+    }
+
+    private int putKey(String key) {
+        if (key == null) {
+            return -1;
+        }
+        int pos = bb.position();
+        if ((flags & BUILDER_FLAG_SHARE_KEYS) != 0) {
+            if (keyPool.get(key) == null) {
+                bb.put(key.getBytes(StandardCharsets.UTF_8));
+                bb.put((byte) 0);
+                keyPool.put(key, pos);
+            } else {
+                pos = keyPool.get(key);
+            }
+        } else {
+            bb.put(key.getBytes(StandardCharsets.UTF_8));
+            bb.put((byte) 0);
+            keyPool.put(key, pos);
+        }
+        return pos;
+    }
+
+    /**
+     * Adds a integer into the buff
+     * @param val integer
+     */
+    public void putInt(int val) {
+        putInt(null, val);
+    }
+
+    public void putInt(String key, int val) {
+        putInt(key, (long) val);
+    }
+
+    public void putInt(String key, long val) {
+        int iKey = putKey(key);
+        if (Byte.MIN_VALUE <= val && val <= Byte.MAX_VALUE) {
+            stack.add(Value.int8(iKey, (int) val));
+        } else if (Short.MIN_VALUE <= val && val <= Short.MAX_VALUE) {
+            stack.add(Value.int16(iKey, (int) val));
+        } else if (Integer.MIN_VALUE <= val && val <= Integer.MAX_VALUE) {
+            stack.add(Value.int32(iKey, (int) val));
+        } else {
+            stack.add(Value.int64(iKey, val));
+        }
+    }
+
+    /**
+     * Adds a 64-bit integer into the buff
+     * @param value integer
+     */
+    public void putInt(long value) {
+        putInt(null, value);
+    }
+
+    /**
+     * Adds a unsigned integer into the buff.
+     * @param value integer representing unsigned value
+     */
+    public void putUInt(int value) {
+        putUInt(null, (long) value);
+    }
+
+    /**
+     * Adds a unsigned integer (stored in a signed 64-bit integer) into the buff.
+     * @param value integer representing unsigned value
+     */
+    public void putUInt(long value) {
+        putUInt(null, value);
+    }
+
+    /**
+     * Adds a 64-bit unsigned integer (stored as {@link BigInteger}) into the buff.
+     * Warning: This operation might be very slow.
+     * @param value integer representing unsigned value
+     */
+    public void putUInt64(BigInteger value) {
+        putUInt64(null, value.longValue());
+    }
+
+    private void putUInt64(String key, long value) {
+        stack.add(Value.uInt64(putKey(key), value));
+    }
+
+    private void putUInt(String key, long value) {
+        int iKey = putKey(key);
+        Value vVal;
+
+        int width = widthUInBits(value);
+
+        if (width == WIDTH_8) {
+            vVal = Value.uInt8(iKey, (int)value);
+        } else if (width == WIDTH_16) {
+            vVal = Value.uInt16(iKey, (int)value);
+        } else if (width == WIDTH_32) {
+            vVal = Value.uInt32(iKey, (int)value);
+        } else {
+            vVal = Value.uInt64(iKey, value);
+        }
+        stack.add(vVal);
+    }
+
+    /**
+     * Adds a 32-bit float into the buff.
+     * @param value float representing value
+     */
+    public void putFloat(float value) {
+        putFloat(null, value);
+    }
+
+    public void putFloat(String key, float val) {
+        stack.add(Value.float32(putKey(key), val));
+    }
+
+    /**
+     * Adds a 64-bit float into the buff.
+     * @param value float representing value
+     */
+    public void putFloat(double value) {
+        putFloat(null, value);
+    }
+
+    public void putFloat(String key, double val) {
+        stack.add(Value.float64(putKey(key), val));
+    }
+
+    /**
+     * Adds a String into the buffer
+     * @param value string
+     * @return start position of string in the buffer
+     */
+    public int putString(String value) {
+        return putString(null, value);
+    }
+
+    public int putString(String key, String val) {
+        int iKey = putKey(key);
+        if ((flags & FlexBuffersBuilder.BUILDER_FLAG_SHARE_STRINGS) != 0) {
+            Integer i = stringPool.get(val);
+            if (i == null) {
+                Value value = writeString(iKey, val);
+                stringPool.put(val, (int) value.iValue);
+                stack.add(value);
+                return (int) value.iValue;
+            } else {
+                int bitWidth = widthUInBits(val.length());
+                stack.add(Value.blob(iKey, i, FBT_STRING, bitWidth));
+                return i;
+            }
+        } else {
+            Value value = writeString(iKey, val);
+            stack.add(value);
+            return (int) value.iValue;
+        }
+    }
+
+    private Value writeString(int key, String s) {
+        return writeBlob(key, s.getBytes(StandardCharsets.UTF_8), FBT_STRING);
+    }
+
+    // in bits to fit a unsigned int
+    private static int widthUInBits(long len) {
+        if (len <= byteToUnsignedInt((byte)0xff)) return WIDTH_8;
+        if (len <= shortToUnsignedInt((short)0xffff)) return WIDTH_16;
+        if (len <= intToUnsignedLong(0xffff_ffff)) return WIDTH_32;
+        return WIDTH_64;
+    }
+
+    private Value writeBlob(int key, byte[] blob, int type) {
+        int bitWidth = widthUInBits(blob.length);
+        int byteWidth = align(bitWidth);
+        writeInt(blob.length, byteWidth);
+        int sloc = bb.position();
+        bb.put(blob);
+        if (type == FBT_STRING) {
+            bb.put((byte) 0);
+        }
+        return Value.blob(key, sloc, type, bitWidth);
+    }
+
+    // Align to prepare for writing a scalar with a certain size.
+    private int align(int alignment) {
+        int byteWidth = 1 << alignment;
+        int padBytes = Value.paddingBytes(bb.capacity(), byteWidth);
+        while (padBytes-- != 0) {
+            bb.put((byte) 0);
+        }
+        return byteWidth;
+    }
+
+    private void writeInt(long value, int byteWidth) {
+        switch (byteWidth) {
+            case 1: bb.put((byte) value); break;
+            case 2: bb.putShort((short) value); break;
+            case 4: bb.putInt((int) value); break;
+            case 8: bb.putLong(value); break;
+        }
+    }
+
+    /**
+     * Adds a byte array into the message
+     * @param value byte array
+     * @return position in buffer as the start of byte array
+     */
+    public int putBlob(byte[] value) {
+        return putBlob(null, value);
+    }
+
+    public int putBlob(String key, byte[] val) {
+        int iKey = putKey(key);
+        Value value = writeBlob(iKey, val, FBT_BLOB);
+        stack.add(value);
+        return (int) value.iValue;
+    }
+
+    public int startVector() {
+        return stack.size();
+    }
+
+    public int endVector(String key, int start, boolean typed, boolean fixed) {
+        int iKey = putKey(key);
+        Value vec = createVector(iKey, start, stack.size() - start, typed, fixed, null);
+        // Remove temp elements and return vector.
+        while (stack.size() > start) {
+            stack.remove(stack.size() - 1);
+        }
+        stack.add(vec);
+        return (int) vec.iValue;
+    }
+
+    /**
+     * Finish writing the message into the buffer. After that no other element must
+     * be inserted into the buffer. Also, you must call this function before start using the
+     * FlexBuffer message
+     * @return ByteBuffer containing the FlexBuffer message
+     */
+    public ByteBuffer finish() {
+        // If you hit this assert, you likely have objects that were never included
+        // in a parent. You need to have exactly one root to finish a buffer.
+        // Check your Start/End calls are matched, and all objects are inside
+        // some other object.
+        assert (stack.size() == 1);
+        // Write root value.
+        int byteWidth = align(stack.get(0).elemWidth(bb.position(), 0));
+        writeAny(stack.get(0), byteWidth);
+        // Write root type.
+        bb.put(stack.get(0).storedPackedType());
+        // Write root size. Normally determined by parent, but root has no parent :)
+        bb.put((byte) byteWidth);
+        bb.limit(bb.position());
+        this.finished = true;
+        return bb;
+    }
+
+    /*
+     * Create a vector based on the elements stored in the stack
+     *
+     * @param key reference to its key
+     * @param start  element in the stack
+     * @param length size of the vector
+     * @param typed  whether is TypedVector or not
+     * @param fixed  whether is Fixed vector or not
+     * @param keys Value representing key vector
+     * @return Value representing the created vector
+     */
+    private Value createVector(int key, int start, int length, boolean typed, boolean fixed, Value keys) {
+        assert (!fixed || typed); // typed=false, fixed=true combination is not supported.
+        // Figure out smallest bit width we can store this vector with.
+        int bitWidth = Math.max(WIDTH_8, widthUInBits(length));
+        int prefixElems = 1;
+        if (keys != null) {
+            // If this vector is part of a map, we will pre-fix an offset to the keys
+            // to this vector.
+            bitWidth = Math.max(bitWidth, keys.elemWidth(bb.position(), 0));
+            prefixElems += 2;
+        }
+        int vectorType = FBT_KEY;
+        // Check bit widths and types for all elements.
+        for (int i = start; i < stack.size(); i++) {
+            int elemWidth = stack.get(i).elemWidth(bb.position(), i + prefixElems);
+            bitWidth = Math.max(bitWidth, elemWidth);
+            if (typed) {
+                if (i == start) {
+                    vectorType = stack.get(i).type;
+                } else {
+                    // If you get this assert, you are writing a typed vector with
+                    // elements that are not all the same type.
+                    assert (vectorType == stack.get(i).type);
+                }
+            }
+        }
+        // If you get this assert, your fixed types are not one of:
+        // Int / UInt / Float / Key.
+        assert (!fixed || FlexBuffers.isTypedVectorElementType(vectorType));
+
+        int byteWidth = align(bitWidth);
+        // Write vector. First the keys width/offset if available, and size.
+        if (keys != null) {
+            writeOffset(keys.iValue, byteWidth);
+            writeInt(1L << keys.minBitWidth, byteWidth);
+        }
+        if (!fixed) {
+            writeInt(length, byteWidth);
+        }
+        // Then the actual data.
+        int vloc = bb.position();
+        for (int i = start; i < stack.size(); i++) {
+            writeAny(stack.get(i), byteWidth);
+        }
+        // Then the types.
+        if (!typed) {
+            for (int i = start; i < stack.size(); i++) {
+                bb.put(stack.get(i).storedPackedType(bitWidth));
+            }
+        }
+        return new Value(key, keys != null ? FBT_MAP
+                : (typed ? FlexBuffers.toTypedVector(vectorType, fixed ? length : 0)
+                : FBT_VECTOR), bitWidth, vloc);
+    }
+
+    private void writeOffset(long val, int byteWidth) {
+        int reloff = (int) (bb.position() - val);
+        assert (byteWidth == 8 || reloff < 1L << (byteWidth * 8));
+        writeInt(reloff, byteWidth);
+    }
+
+    private void writeAny(final Value val, int byteWidth) {
+        switch (val.type) {
+            case FBT_NULL:
+            case FBT_BOOL:
+            case FBT_INT:
+            case FBT_UINT:
+                writeInt(val.iValue, byteWidth);
+                break;
+            case FBT_FLOAT:
+                writeDouble(val.dValue, byteWidth);
+                break;
+            default:
+                writeOffset(val.iValue, byteWidth);
+                break;
+        }
+    }
+
+    private void writeDouble(double val, int byteWidth) {
+        if (byteWidth == 4) {
+            bb.putFloat((float) val);
+        } else if (byteWidth == 8) {
+            bb.putDouble(val);
+        }
+    }
+
+    public int startMap() {
+        return stack.size();
+    }
+
+    public int endMap(String key, int start) {
+        int iKey = putKey(key);
+
+        Collections.sort(stack.subList(start, stack.size()), valueComparator);
+
+        Value keys = createKeyVector(start, stack.size() - start);
+        Value vec = createVector(iKey, start, stack.size() - start, false, false, keys);
+        // Remove temp elements and return map.
+        while (stack.size() > start) {
+            stack.remove(stack.size() - 1);
+        }
+        stack.add(vec);
+        return (int) vec.iValue;
+    }
+
+    private Value createKeyVector(int start, int length) {
+        // Figure out smallest bit width we can store this vector with.
+        int bitWidth = Math.max(WIDTH_8, widthUInBits(length));
+        int prefixElems = 1;
+        // Check bit widths and types for all elements.
+        for (int i = start; i < stack.size(); i++) {
+            int elemWidth = Value.elemWidth(FBT_KEY, WIDTH_8, stack.get(i).key, bb.position(), i + prefixElems);
+            bitWidth = Math.max(bitWidth, elemWidth);
+        }
+
+        int byteWidth = align(bitWidth);
+        // Write vector. First the keys width/offset if available, and size.
+        writeInt(length, byteWidth);
+        // Then the actual data.
+        int vloc = bb.position();
+        for (int i = start; i < stack.size(); i++) {
+            int pos = stack.get(i).key;
+            assert(pos != -1);
+            writeOffset(stack.get(i).key, byteWidth);
+        }
+        // Then the types.
+        return new Value(-1, FlexBuffers.toTypedVector(FBT_KEY,0), bitWidth, vloc);
+    }
+
+    public static class Value {
+        final int type;
+        // for scalars, represents scalar size in bytes
+        // for vectors, represents the size
+        // for string, length
+        final int minBitWidth;
+        // float value
+        final double dValue;
+        // integer value
+        long iValue;
+        // position of the key associated with this value in buffer
+        int key;
+
+        Value(int key, int type, int bitWidth, long iValue) {
+            this.key = key;
+            this.type = type;
+            this.minBitWidth = bitWidth;
+            this.iValue = iValue;
+            this.dValue = Double.MIN_VALUE;
+        }
+
+        Value(int key, int type, int bitWidth, double dValue) {
+            this.key = key;
+            this.type = type;
+            this.minBitWidth = bitWidth;
+            this.dValue = dValue;
+            this.iValue = Long.MIN_VALUE;
+        }
+
+        static Value bool(int key, boolean b) {
+            return new Value(key, FBT_BOOL, WIDTH_8, b ? 1 : 0);
+        }
+
+        static Value blob(int key, int position, int type, int bitWidth) {
+            return new Value(key, type, WIDTH_8, position);
+        }
+
+        static Value int8(int key, int value) {
+            return new Value(key, FBT_INT, WIDTH_8, value);
+        }
+
+        static Value int16(int key, int value) {
+            return new Value(key, FBT_INT, WIDTH_16, value);
+        }
+
+        static Value int32(int key, int value) {
+            return new Value(key, FBT_INT, WIDTH_32, value);
+        }
+
+        static Value int64(int key, long value) {
+            return new Value(key, FBT_INT, WIDTH_64, value);
+        }
+
+        static Value uInt8(int key, int value) {
+            return new Value(key, FBT_UINT, WIDTH_8, value);
+        }
+
+        static Value uInt16(int key, int value) {
+            return new Value(key, FBT_UINT, WIDTH_16, value);
+        }
+
+        static Value uInt32(int key, int value) {
+            return new Value(key, FBT_UINT, WIDTH_32, value);
+        }
+
+        static Value uInt64(int key, long value) {
+            return new Value(key, FBT_UINT, WIDTH_64, value);
+        }
+
+        static Value float32(int key, float value) {
+            return new Value(key, FBT_FLOAT, WIDTH_32, value);
+        }
+
+        static Value float64(int key, double value) {
+            return new Value(key, FBT_FLOAT, WIDTH_64, value);
+        }
+
+        private byte storedPackedType() {
+            return storedPackedType(WIDTH_8);
+        }
+
+        private byte storedPackedType(int parentBitWidth) {
+            return packedType(storedWidth(parentBitWidth), type);
+        }
+
+        private static byte packedType(int bitWidth, int type) {
+            return (byte) (bitWidth | (type << 2));
+        }
+
+        private int storedWidth(int parentBitWidth) {
+            if (FlexBuffers.isTypeInline(type)) {
+                return Math.max(minBitWidth, parentBitWidth);
+            } else {
+                return minBitWidth;
+            }
+        }
+
+        private int elemWidth(int bufSize, int elemIndex) {
+            return elemWidth(type, minBitWidth, iValue, bufSize, elemIndex);
+        }
+
+        private static int elemWidth(int type, int minBitWidth, long iValue, int bufSize, int elemIndex) {
+            if (FlexBuffers.isTypeInline(type)) {
+                return minBitWidth;
+            } else {
+                // We have an absolute offset, but want to store a relative offset
+                // elem_index elements beyond the current buffer end. Since whether
+                // the relative offset fits in a certain byte_width depends on
+                // the size of the elements before it (and their alignment), we have
+                // to test for each size in turn.
+
+                // Original implementation checks for largest scalar
+                // which is long unsigned int
+                for (int byteWidth = 1; byteWidth <= 32; byteWidth *= 2) {
+                    // Where are we going to write this offset?
+                    int offsetLoc = bufSize + paddingBytes(bufSize, byteWidth) + (elemIndex * byteWidth);
+                    // Compute relative offset.
+                    long offset = offsetLoc - iValue;
+                    // Does it fit?
+                    int bitWidth = widthUInBits((int) offset);
+                    if (((1L) << bitWidth) == byteWidth)
+                        return bitWidth;
+                }
+                assert (false);  // Must match one of the sizes above.
+                return WIDTH_64;
+            }
+        }
+
+        private static int paddingBytes(int bufSize, int scalarSize) {
+            return ((~bufSize) + 1) & (scalarSize - 1);
+        }
+    }
+}