import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class Main {
  public static void main(String args[]) throws Exception {
    Connection con = null;
    Class.forName("oracle.jdbc.driver.OracleDriver");
    con = DriverManager.getConnection(
        "jdbc:oracle:thin:@192.201.32.92:1521:psprd1", "username", "password");
    String query = null;
    ResultSet rset = null;
    query = "UPDATE t1 " + " SET id = ?";
    PreparedStatement stmt = con.prepareStatement(query);
    // stmt.setInt(paramIndex++, null);
    stmt.setNull(1, java.sql.Types.INTEGER);
    stmt.executeUpdate();
    stmt.close();
    query = "select id from t1 ";
    stmt = con.prepareStatement(query);
    rset = stmt.executeQuery();
    rset.next();
    System.out.println(rset.getString("id"));
    rset.close();
    stmt.close();
    con.close();
  }
}

SQL

create table t1 (id number default 1 );
insert into t1 (id) values (2);