JAVA连接MYSQL,使用PreparedStatement 写查询,修改,添加,删除,语句

PreparedStatement ps=conn.prepareStatement("insert into Goods (Gname,Gprice,Gamount,Gdate,Gperson) values (?,?,?,?,?)");
ps.setString(1,goods.getGname());
ps.setInt(2,goods.getGprice());
ps.setInt(3,goods.getGamount());
ps.setString(4,goods.getGdate());
ps.setString(5,goods.getGperson());
i=ps.executeUpdate();

PreparedStatement ps=conn.prepareStatement("select * from USERMSG where username=? and password=?");
ps.setString(1,username);
ps.setString(2,password);
rs=ps.executeQuery();

PreparedStatement ps=conn.prepareStatement("update Goods set Gname=?,Gprice=?,Gamount=?,Gdate=?,Gperson=?  where Gid=?");
ps.setString(1,goods.getGname());
ps.setInt(2,goods.getGprice());
ps.setInt(3,goods.getGamount());
ps.setString(4,goods.getGdate());
ps.setString(5,goods.getGperson());
ps.setInt(6,goods.getId());
i=ps.executeUpdate();

PreparedStatement ps=conn.prepareStatement("delete from Goods where Gid=?");
ps.setString(1,username);
rs=ps.executeQuery();