Java: Calculation of vtable and vtable size moved to the __init method. (#5210)

vtable and vtable size depends only on `Table#bb_pos` but calculated in
`Table#_offset` method on each field lookup.
Doing this with every call of `Table#__offset` is redundant.

These values can be read once with change of `Table#bb_pos` and reused
for any field lookup.

java/com/google/flatbuffers/Table.java

@@ -37,6 +37,10 @@ public class Table {
   protected int bb_pos;
   /** The underlying ByteBuffer to hold the data of the Table. */
   protected ByteBuffer bb;
+  /** Used to hold the vtable position. */
+  protected int vtable_start;
+  /** Used to hold the vtable size. */
+  protected int vtable_size;
   Utf8 utf8 = Utf8.getDefault();
 
   /**
@@ -53,8 +57,7 @@ public class Table {
    * @return Returns an offset into the object, or `0` if the field is not present.
    */
   protected int __offset(int vtable_offset) {
-    int vtable = bb_pos - bb.getInt(bb_pos);
-    return vtable_offset < bb.getShort(vtable) ? bb.getShort(vtable + vtable_offset) : 0;
+    return vtable_offset < vtable_size ? bb.getShort(vtable_start + vtable_offset) : 0;
   }
 
   protected static int __offset(int vtable_offset, int offset, ByteBuffer bb) {
@@ -169,6 +172,8 @@ public class Table {
     offset += bb_pos;
     t.bb_pos = offset + bb.getInt(offset);
     t.bb = bb;
+    t.vtable_start = t.bb_pos - bb.getInt(t.bb_pos);
+    t.vtable_size = bb.getShort(t.vtable_start);
     return t;
   }
 
@@ -268,6 +273,8 @@ public class Table {
   public void __reset() {
     bb = null;
     bb_pos = 0;
+    vtable_start = 0;
+    vtable_size = 0;
   }
 }
 

src/idl_gen_general.cpp

@@ -874,7 +874,15 @@ class GeneralGenerator : public BaseGenerator {
     // accessor object. This is to allow object reuse.
     code += "  public void __init(int _i, ByteBuffer _bb) ";
     code += "{ " + lang_.accessor_prefix + "bb_pos = _i; ";
-    code += lang_.accessor_prefix + "bb = _bb; }\n";
+    code += lang_.accessor_prefix + "bb = _bb; ";
+    if (!struct_def.fixed && lang_.language == IDLOptions::kJava) {
+      code += lang_.accessor_prefix + "vtable_start = " + lang_.accessor_prefix + "bb_pos - ";
+      code += lang_.accessor_prefix + "bb." + FunctionStart('G') + "etInt(";
+      code += lang_.accessor_prefix + "bb_pos); " + lang_.accessor_prefix + "vtable_size = ";
+      code += lang_.accessor_prefix + "bb." + FunctionStart('G') + "etShort(";
+      code += lang_.accessor_prefix + "vtable_start); ";
+    }
+    code += "}\n";
     code +=
         "  public " + struct_def.name + " __assign(int _i, ByteBuffer _bb) ";
     code += "{ __init(_i, _bb); return this; }\n\n";

tests/MyGame/Example/Monster.java

@@ -15,7 +15,7 @@ public final class Monster extends Table {
   public static Monster getRootAsMonster(ByteBuffer _bb) { return getRootAsMonster(_bb, new Monster()); }
   public static Monster getRootAsMonster(ByteBuffer _bb, Monster obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
   public static boolean MonsterBufferHasIdentifier(ByteBuffer _bb) { return __has_identifier(_bb, "MONS"); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public Monster __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public Vec3 pos() { return pos(new Vec3()); }

tests/MyGame/Example/Referrable.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class Referrable extends Table {
   public static Referrable getRootAsReferrable(ByteBuffer _bb) { return getRootAsReferrable(_bb, new Referrable()); }
   public static Referrable getRootAsReferrable(ByteBuffer _bb, Referrable obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public Referrable __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public long id() { int o = __offset(4); return o != 0 ? bb.getLong(o + bb_pos) : 0L; }

tests/MyGame/Example/Stat.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class Stat extends Table {
   public static Stat getRootAsStat(ByteBuffer _bb) { return getRootAsStat(_bb, new Stat()); }
   public static Stat getRootAsStat(ByteBuffer _bb, Stat obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public Stat __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public String id() { int o = __offset(4); return o != 0 ? __string(o + bb_pos) : null; }

tests/MyGame/Example/TestSimpleTableWithEnum.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 final class TestSimpleTableWithEnum extends Table {
   public static TestSimpleTableWithEnum getRootAsTestSimpleTableWithEnum(ByteBuffer _bb) { return getRootAsTestSimpleTableWithEnum(_bb, new TestSimpleTableWithEnum()); }
   public static TestSimpleTableWithEnum getRootAsTestSimpleTableWithEnum(ByteBuffer _bb, TestSimpleTableWithEnum obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public TestSimpleTableWithEnum __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public byte color() { int o = __offset(4); return o != 0 ? bb.get(o + bb_pos) : 2; }

tests/MyGame/Example/TypeAliases.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class TypeAliases extends Table {
   public static TypeAliases getRootAsTypeAliases(ByteBuffer _bb) { return getRootAsTypeAliases(_bb, new TypeAliases()); }
   public static TypeAliases getRootAsTypeAliases(ByteBuffer _bb, TypeAliases obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public TypeAliases __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public byte i8() { int o = __offset(4); return o != 0 ? bb.get(o + bb_pos) : 0; }

tests/MyGame/Example2/Monster.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class Monster extends Table {
   public static Monster getRootAsMonster(ByteBuffer _bb) { return getRootAsMonster(_bb, new Monster()); }
   public static Monster getRootAsMonster(ByteBuffer _bb, Monster obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public Monster __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
 

tests/MyGame/InParentNamespace.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class InParentNamespace extends Table {
   public static InParentNamespace getRootAsInParentNamespace(ByteBuffer _bb) { return getRootAsInParentNamespace(_bb, new InParentNamespace()); }
   public static InParentNamespace getRootAsInParentNamespace(ByteBuffer _bb, InParentNamespace obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public InParentNamespace __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
 

tests/MyGame/MonsterExtra.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class MonsterExtra extends Table {
   public static MonsterExtra getRootAsMonsterExtra(ByteBuffer _bb) { return getRootAsMonsterExtra(_bb, new MonsterExtra()); }
   public static MonsterExtra getRootAsMonsterExtra(ByteBuffer _bb, MonsterExtra obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public MonsterExtra __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public float testfNan() { int o = __offset(4); return o != 0 ? bb.getFloat(o + bb_pos) : Float.NaN; }

tests/generate_code.bat

@@ -17,7 +17,7 @@ if "%1"=="-b" set buildtype=%2
 
 ..\%buildtype%\flatc.exe --cpp --java --csharp --go --binary --python --lobster --lua --js --rust --ts --php --grpc --gen-mutable --reflect-names --gen-object-api --gen-compare --no-includes --cpp-ptr-type flatbuffers::unique_ptr --no-fb-import -I include_test monster_test.fbs monsterdata_test.json || goto FAIL
 ..\%buildtype%\flatc.exe --cpp --java --csharp --go --binary --python --lobster --lua --js --rust --ts --php --gen-mutable --reflect-names --no-fb-import --cpp-ptr-type flatbuffers::unique_ptr  -o namespace_test namespace_test/namespace_test1.fbs namespace_test/namespace_test2.fbs || goto FAIL
-..\%buildtype%\flatc.exe --cpp --js --ts --php --gen-mutable --reflect-names --gen-object-api --gen-compare --cpp-ptr-type flatbuffers::unique_ptr -o union_vector ./union_vector/union_vector.fbs || goto FAIL
+..\%buildtype%\flatc.exe --cpp --java --js --ts --php --gen-mutable --reflect-names --gen-object-api --gen-compare --cpp-ptr-type flatbuffers::unique_ptr -o union_vector ./union_vector/union_vector.fbs || goto FAIL
 ..\%buildtype%\flatc.exe -b --schema --bfbs-comments --bfbs-builtins -I include_test monster_test.fbs || goto FAIL
 ..\%buildtype%\flatc.exe --jsonschema --schema -I include_test monster_test.fbs || goto FAIL
 

tests/generate_code.sh

@@ -17,7 +17,7 @@ set -e
 
 ../flatc --cpp --java --csharp --dart --go --binary --lobster --lua --python --js --ts --php --rust --grpc --gen-mutable --reflect-names --gen-object-api --gen-compare --no-includes --cpp-ptr-type flatbuffers::unique_ptr  --no-fb-import -I include_test monster_test.fbs monsterdata_test.json
 ../flatc --cpp --java --csharp --dart --go --binary --lobster --lua --python --js --ts --php --rust --gen-mutable --reflect-names --no-fb-import --cpp-ptr-type flatbuffers::unique_ptr  -o namespace_test namespace_test/namespace_test1.fbs namespace_test/namespace_test2.fbs
-../flatc --cpp --js --ts --php --gen-mutable --reflect-names --gen-object-api --gen-compare --cpp-ptr-type flatbuffers::unique_ptr -o union_vector ./union_vector/union_vector.fbs
+../flatc --cpp --java --js --ts --php --gen-mutable --reflect-names --gen-object-api --gen-compare --cpp-ptr-type flatbuffers::unique_ptr -o union_vector ./union_vector/union_vector.fbs
 ../flatc -b --schema --bfbs-comments --bfbs-builtins -I include_test monster_test.fbs
 ../flatc --jsonschema --schema -I include_test monster_test.fbs
 ../flatc --cpp --java --csharp --python --gen-mutable --reflect-names --gen-object-api --gen-compare --no-includes monster_extra.fbs || goto FAIL

tests/namespace_test/NamespaceA/NamespaceB/TableInNestedNS.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class TableInNestedNS extends Table {
   public static TableInNestedNS getRootAsTableInNestedNS(ByteBuffer _bb) { return getRootAsTableInNestedNS(_bb, new TableInNestedNS()); }
   public static TableInNestedNS getRootAsTableInNestedNS(ByteBuffer _bb, TableInNestedNS obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public TableInNestedNS __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public int foo() { int o = __offset(4); return o != 0 ? bb.getInt(o + bb_pos) : 0; }

tests/namespace_test/NamespaceA/SecondTableInA.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class SecondTableInA extends Table {
   public static SecondTableInA getRootAsSecondTableInA(ByteBuffer _bb) { return getRootAsSecondTableInA(_bb, new SecondTableInA()); }
   public static SecondTableInA getRootAsSecondTableInA(ByteBuffer _bb, SecondTableInA obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public SecondTableInA __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public NamespaceC.TableInC referToC() { return referToC(new NamespaceC.TableInC()); }

tests/namespace_test/NamespaceA/TableInFirstNS.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class TableInFirstNS extends Table {
   public static TableInFirstNS getRootAsTableInFirstNS(ByteBuffer _bb) { return getRootAsTableInFirstNS(_bb, new TableInFirstNS()); }
   public static TableInFirstNS getRootAsTableInFirstNS(ByteBuffer _bb, TableInFirstNS obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public TableInFirstNS __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public NamespaceA.NamespaceB.TableInNestedNS fooTable() { return fooTable(new NamespaceA.NamespaceB.TableInNestedNS()); }

tests/namespace_test/NamespaceC/TableInC.java

@@ -11,7 +11,7 @@ import com.google.flatbuffers.*;
 public final class TableInC extends Table {
   public static TableInC getRootAsTableInC(ByteBuffer _bb) { return getRootAsTableInC(_bb, new TableInC()); }
   public static TableInC getRootAsTableInC(ByteBuffer _bb, TableInC obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public TableInC __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public NamespaceA.TableInFirstNS referToA1() { return referToA1(new NamespaceA.TableInFirstNS()); }

tests/union_vector/Attacker.java

@@ -9,10 +9,11 @@ import com.google.flatbuffers.*;
 public final class Attacker extends Table {
   public static Attacker getRootAsAttacker(ByteBuffer _bb) { return getRootAsAttacker(_bb, new Attacker()); }
   public static Attacker getRootAsAttacker(ByteBuffer _bb, Attacker obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public Attacker __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public int swordAttackDamage() { int o = __offset(4); return o != 0 ? bb.getInt(o + bb_pos) : 0; }
+  public boolean mutateSwordAttackDamage(int sword_attack_damage) { int o = __offset(4); if (o != 0) { bb.putInt(o + bb_pos, sword_attack_damage); return true; } else { return false; } }
 
   public static int createAttacker(FlatBufferBuilder builder,
       int sword_attack_damage) {

tests/union_vector/BookReader.java

@@ -11,6 +11,7 @@ public final class BookReader extends Struct {
   public BookReader __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public int booksRead() { return bb.getInt(bb_pos + 0); }
+  public void mutateBooksRead(int books_read) { bb.putInt(bb_pos + 0, books_read); }
 
   public static int createBookReader(FlatBufferBuilder builder, int booksRead) {
     builder.prep(4, 4);

tests/union_vector/Movie.java

@@ -10,15 +10,17 @@ public final class Movie extends Table {
   public static Movie getRootAsMovie(ByteBuffer _bb) { return getRootAsMovie(_bb, new Movie()); }
   public static Movie getRootAsMovie(ByteBuffer _bb, Movie obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
   public static boolean MovieBufferHasIdentifier(ByteBuffer _bb) { return __has_identifier(_bb, "MOVI"); }
-  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; }
+  public void __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; vtable_start = bb_pos - bb.getInt(bb_pos); vtable_size = bb.getShort(vtable_start); }
   public Movie __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public byte mainCharacterType() { int o = __offset(4); return o != 0 ? bb.get(o + bb_pos) : 0; }
+  public boolean mutateMainCharacterType(byte main_character_type) { int o = __offset(4); if (o != 0) { bb.put(o + bb_pos, main_character_type); return true; } else { return false; } }
   public Table mainCharacter(Table obj) { int o = __offset(6); return o != 0 ? __union(obj, o) : null; }
   public byte charactersType(int j) { int o = __offset(8); return o != 0 ? bb.get(__vector(o) + j * 1) : 0; }
   public int charactersTypeLength() { int o = __offset(8); return o != 0 ? __vector_len(o) : 0; }
   public ByteBuffer charactersTypeAsByteBuffer() { return __vector_as_bytebuffer(8, 1); }
   public ByteBuffer charactersTypeInByteBuffer(ByteBuffer _bb) { return __vector_in_bytebuffer(_bb, 8, 1); }
+  public boolean mutateCharactersType(int j, byte characters_type) { int o = __offset(8); if (o != 0) { bb.put(__vector(o) + j * 1, characters_type); return true; } else { return false; } }
   public Table characters(Table obj, int j) { int o = __offset(10); return o != 0 ? __union(obj, __vector(o) + j * 4 - bb_pos) : null; }
   public int charactersLength() { int o = __offset(10); return o != 0 ? __vector_len(o) : 0; }
 

tests/union_vector/Rapunzel.java

@@ -11,6 +11,7 @@ public final class Rapunzel extends Struct {
   public Rapunzel __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
 
   public int hairLength() { return bb.getInt(bb_pos + 0); }
+  public void mutateHairLength(int hair_length) { bb.putInt(bb_pos + 0, hair_length); }
 
   public static int createRapunzel(FlatBufferBuilder builder, int hairLength) {
     builder.prep(4, 4);