Fixed possible alignment issue in Java

Tested: on Linux

Change-Id: Ie80aa19ed13ac4fa15cd3fd768f1a35526bdc607

java/flatbuffers/FlatBufferBuilder.java

@@ -123,10 +123,11 @@ public class FlatBufferBuilder {
         putInt(off);
     }
 
-    public void startVector(int elem_size, int num_elems) {
+    public void startVector(int elem_size, int num_elems, int alignment) {
         notNested();
         vector_num_elems = num_elems;
         prep(SIZEOF_INT, elem_size * num_elems);
+        prep(alignment, elem_size * num_elems); // Just in case alignment > int.
     }
 
     public int endVector() {
@@ -137,7 +138,7 @@ public class FlatBufferBuilder {
     public int createString(String s) {
         byte[] utf8 = s.getBytes(utf8charset);
         addByte((byte)0);
-        startVector(1, utf8.length);
+        startVector(1, utf8.length, 1);
         System.arraycopy(utf8, 0, bb.array(), space -= utf8.length, utf8.length);
         return endVector();
     }

src/idl_gen_java.cpp

@@ -320,8 +320,12 @@ static void GenStruct(StructDef &struct_def,
         code += "  public static void start" + MakeCamel(field.name);
         code += "Vector(FlatBufferBuilder builder, int numElems) ";
         code += "{ builder.startVector(";
-        code += NumToString(InlineSize(field.value.type.VectorType()));
+        auto vector_type = field.value.type.VectorType();
-        code += ", numElems); }\n";
+        auto alignment = InlineAlignment(vector_type);
+        auto elem_size = InlineSize(vector_type);
+        code += NumToString(elem_size);
+        code += ", numElems, " + NumToString(alignment);
+        code += "); }\n";
       }
     }
     code += "  public static int end" + struct_def.name;

tests/MyGame/Example/Monster.java

@@ -33,26 +33,29 @@ public class Monster extends Table {
   public Monster enemy(Monster obj) { int o = __offset(28); return o != 0 ? obj.__init(__indirect(o + bb_pos), bb) : null; }
   public byte testnestedflatbuffer(int j) { int o = __offset(30); return o != 0 ? bb.get(__vector(o) + j * 1) : 0; }
   public int testnestedflatbufferLength() { int o = __offset(30); return o != 0 ? __vector_len(o) : 0; }
+  public Monster testempty() { return testempty(new Monster()); }
+  public Monster testempty(Monster obj) { int o = __offset(32); return o != 0 ? obj.__init(__indirect(o + bb_pos), bb) : null; }
 
-  public static void startMonster(FlatBufferBuilder builder) { builder.startObject(14); }
+  public static void startMonster(FlatBufferBuilder builder) { builder.startObject(15); }
   public static void addPos(FlatBufferBuilder builder, int posOffset) { builder.addStruct(0, posOffset, 0); }
   public static void addMana(FlatBufferBuilder builder, short mana) { builder.addShort(1, mana, 150); }
   public static void addHp(FlatBufferBuilder builder, short hp) { builder.addShort(2, hp, 100); }
   public static void addName(FlatBufferBuilder builder, int nameOffset) { builder.addOffset(3, nameOffset, 0); }
   public static void addInventory(FlatBufferBuilder builder, int inventoryOffset) { builder.addOffset(5, inventoryOffset, 0); }
-  public static void startInventoryVector(FlatBufferBuilder builder, int numElems) { builder.startVector(1, numElems); }
+  public static void startInventoryVector(FlatBufferBuilder builder, int numElems) { builder.startVector(1, numElems, 1); }
   public static void addColor(FlatBufferBuilder builder, byte color) { builder.addByte(6, color, 8); }
   public static void addTestType(FlatBufferBuilder builder, byte testType) { builder.addByte(7, testType, 0); }
   public static void addTest(FlatBufferBuilder builder, int testOffset) { builder.addOffset(8, testOffset, 0); }
   public static void addTest4(FlatBufferBuilder builder, int test4Offset) { builder.addOffset(9, test4Offset, 0); }
-  public static void startTest4Vector(FlatBufferBuilder builder, int numElems) { builder.startVector(4, numElems); }
+  public static void startTest4Vector(FlatBufferBuilder builder, int numElems) { builder.startVector(4, numElems, 2); }
   public static void addTestarrayofstring(FlatBufferBuilder builder, int testarrayofstringOffset) { builder.addOffset(10, testarrayofstringOffset, 0); }
-  public static void startTestarrayofstringVector(FlatBufferBuilder builder, int numElems) { builder.startVector(4, numElems); }
+  public static void startTestarrayofstringVector(FlatBufferBuilder builder, int numElems) { builder.startVector(4, numElems, 4); }
   public static void addTestarrayoftables(FlatBufferBuilder builder, int testarrayoftablesOffset) { builder.addOffset(11, testarrayoftablesOffset, 0); }
-  public static void startTestarrayoftablesVector(FlatBufferBuilder builder, int numElems) { builder.startVector(4, numElems); }
+  public static void startTestarrayoftablesVector(FlatBufferBuilder builder, int numElems) { builder.startVector(4, numElems, 4); }
   public static void addEnemy(FlatBufferBuilder builder, int enemyOffset) { builder.addOffset(12, enemyOffset, 0); }
   public static void addTestnestedflatbuffer(FlatBufferBuilder builder, int testnestedflatbufferOffset) { builder.addOffset(13, testnestedflatbufferOffset, 0); }
-  public static void startTestnestedflatbufferVector(FlatBufferBuilder builder, int numElems) { builder.startVector(1, numElems); }
+  public static void startTestnestedflatbufferVector(FlatBufferBuilder builder, int numElems) { builder.startVector(1, numElems, 1); }
+  public static void addTestempty(FlatBufferBuilder builder, int testemptyOffset) { builder.addOffset(14, testemptyOffset, 0); }
   public static int endMonster(FlatBufferBuilder builder) { return builder.endObject(); }
 };