[java] simplify (and probably speedup) Type.createEmptyInstance

std/java/_std/Type.hx

@@ -243,11 +243,18 @@ enum ValueType {
 		return null;
 	}
 
-	public static function createEmptyInstance<T>( cl : Class<T> ) : T untyped
-	{
-		if (Reflect.hasField(cl, "__hx_createEmpty"))
-			return cl.__hx_createEmpty();
-		return createInstance(cl, []);
+	// cache empty constructor arguments so we don't allocate it on each createEmptyInstance call
+	@:protected @:readOnly static var __createEmptyInstance_EMPTY_TYPES = java.NativeArray.make(java.Lib.toNativeEnum(java.internal.Runtime.EmptyObject));
+	@:protected @:readOnly static var __createEmptyInstance_EMPTY_ARGS = java.NativeArray.make(java.internal.Runtime.EmptyObject.EMPTY);
+
+	public static function createEmptyInstance<T>( cl : Class<T> ) : T {
+		var t = java.Lib.toNativeType(cl);
+		try {
+			var ctor = t.getConstructor(__createEmptyInstance_EMPTY_TYPES);
+			return ctor.newInstance(__createEmptyInstance_EMPTY_ARGS);
+		} catch (_:java.lang.NoSuchMethodException) {
+			return t.newInstance();
+		}
 	}
 
 	@:functionCode('

std/java/internal/Runtime.hx

@@ -584,7 +584,7 @@ package java.internal;
 	}
 }
 
-@:keep @:native("haxe.lang.EmptyObject") private enum EmptyObject
+@:keep @:native("haxe.lang.EmptyObject") enum EmptyObject
 {
 	EMPTY;
 }