gistfile1.java

        PreparedStatement ps = connection.prepareStatement("INSERT INTO users (first_name, email, last_name) VALUES (?, ?, ?)", new String[]{"id"});
        ps.setObject(1, "John");
        ps.setObject(2, "Doe");
        ps.setObject(3, "john@doe.com");

        ps.executeUpdate();

        ResultSet rs = ps.getGeneratedKeys();
        rs.next();
        Object id = rs.getObject(1);
        System.out.println("Generated Id value: " + id);
        System.out.println("Generated Id class: " + id.getClass());


        Statement s = connection.createStatement();
        ResultSet rs1 = s.executeQuery("select * from users");
        rs1.next();

        Object realId = rs1.getObject("id");
        System.out.println("realId Id value: " + realId);
        System.out.println("realId Id class: " + realId.getClass());

Output:
Generated Id value: 1
Generated Id class: class java.lang.Long
realId Id value: 1
realId Id class: class java.lang.Integer