Added force-defaults to Java bindings

Change-Id: I62d10b639112788be3b0f670280bd50ef9fcf094

java/com/google/flatbuffers/FlatBufferBuilder.java

@@ -39,6 +39,7 @@ public class FlatBufferBuilder {
     int[] vtables = new int[16];  // List of offsets of all vtables.
     int num_vtables = 0;          // Number of entries in `vtables` in use.
     int vector_num_elems = 0;     // For the current vector being built.
+    boolean force_defaults = false; // False omits default values from the serialized data
 
    /**
     * Start with a buffer of size {@code initial_size}, then grow as required.
@@ -333,14 +334,14 @@ public class FlatBufferBuilder {
     }
 
     // Add a scalar to a table at `o` into its vtable, with value `x` and default `d`
-    public void addBoolean(int o, boolean x, boolean d) { if(x != d) { addBoolean(x); slot(o); } }
-    public void addByte   (int o, byte    x, int     d) { if(x != d) { addByte   (x); slot(o); } }
-    public void addShort  (int o, short   x, int     d) { if(x != d) { addShort  (x); slot(o); } }
-    public void addInt    (int o, int     x, int     d) { if(x != d) { addInt    (x); slot(o); } }
-    public void addLong   (int o, long    x, long    d) { if(x != d) { addLong   (x); slot(o); } }
-    public void addFloat  (int o, float   x, double  d) { if(x != d) { addFloat  (x); slot(o); } }
-    public void addDouble (int o, double  x, double  d) { if(x != d) { addDouble (x); slot(o); } }
-    public void addOffset (int o, int     x, int     d) { if(x != d) { addOffset (x); slot(o); } }
+    public void addBoolean(int o, boolean x, boolean d) { if(force_defaults || x != d) { addBoolean(x); slot(o); } }
+    public void addByte   (int o, byte    x, int     d) { if(force_defaults || x != d) { addByte   (x); slot(o); } }
+    public void addShort  (int o, short   x, int     d) { if(force_defaults || x != d) { addShort  (x); slot(o); } }
+    public void addInt    (int o, int     x, int     d) { if(force_defaults || x != d) { addInt    (x); slot(o); } }
+    public void addLong   (int o, long    x, long    d) { if(force_defaults || x != d) { addLong   (x); slot(o); } }
+    public void addFloat  (int o, float   x, double  d) { if(force_defaults || x != d) { addFloat  (x); slot(o); } }
+    public void addDouble (int o, double  x, double  d) { if(force_defaults || x != d) { addDouble (x); slot(o); } }
+    public void addOffset (int o, int     x, int     d) { if(force_defaults || x != d) { addOffset (x); slot(o); } }
 
     // Structs are stored inline, so nothing additional is being added. `d` is always 0.
     public void addStruct(int voffset, int x, int d) {
@@ -442,6 +443,19 @@ public class FlatBufferBuilder {
         finish(root_table);
     }
 
+    /**
+     * In order to save space, fields that are set to their default value
+     * don't get serialized into the buffer. Forcing defaults provides a
+     * way to manually disable this optimization.
+     *
+     * @param forceDefaults true always serializes default values
+     * @return this
+     */
+    public FlatBufferBuilder forceDefaults(boolean forceDefaults){
+        this.force_defaults = forceDefaults;
+        return this;
+    }
+
     // Get the ByteBuffer representing the FlatBuffer. Only call this after you've
     // called finish(). The actual data starts at the ByteBuffer's current position,
     // not necessarily at 0.