JAVA.SQL.SQLEXCEPTION:ORA-00001: Violates the unique constraint (SCOTT. sys_c0011456)

I tb_user the primary key of the database is the ID, in this Java program:

String sql= "INSERT into Tb_user (Id,user_name,user_password) VALUES (User_seq.nextval, '" +un+ "', '" +pw+ "')";

The sequence is also the primary key, the initial value when the sequence is created because the default value of 1 is selected, and the original tb_user has a value

This Java exception is a duplicate of the primary key.

So change the initial value of the modified sequence a bit larger, I will change to 3.

JAVA.SQL.SQLEXCEPTION:ORA-00001: Violates the unique constraint (SCOTT. sys_c0011456)