Query "Merge" freezes on executing. Oracle via jdbc

I have query on merge. When it runs in SqlDeveloper, it executes correctly. But when I trying to execute in java using jdbc, it freezes.

    @Override
    public void updateRegion(int id, int region) {
        try {
            PreparedStatement statement = connection.prepareStatement(
                    "MERGE INTO LINKING_DOCTORS_TO_REGION l "
                    + "USING LINKING_DOCTORS_TO_REGION l1 "
                    + "ON (l1.user_ = ?) "
                    + "WHEN MATCHED THEN UPDATE SET region = ? "
                    + "WHEN NOT MATCHED THEN INSERT (region, user_) VALUES (?, ?)");
            statement.setInt(1, id);
            statement.setInt(4, id);
            statement.setInt(2, region);
            statement.setInt(3, region);
            statement.execute();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

What is wrong? Thanks