删：
Connection conn=SQLHelper.getConnection();
try
{
     String sql="delete from user where username=xiao";
     Statement stm=conn.createStatement();
     stm.execute(sql);
     conn.close();
}
catch(Exception ex)
{
}

查：
ArrayList<user1> list=new ArrayList<user1>();
Connection conn=SQLHelper.getConnection();
try
{
     String sql="select * from user1";
     Statement stm=conn.createStatement();
     ResultSet rs=stm.executeQuery();
    while(rs.next())
   {
            user1 my=new user1();
            user1.setUsername(rs.getString("username"));
            user1.setPasswrd(rs.getString("passwrd"));
            list.add(user1);
    }
     conn.close();
}
catch(Exception ex)
{
}

至于改就是SQL语句用Update ************,跟上面差不多。

直接去网上找个项目吧!

楼上正解