JSP中的输出问题

<HTML>
    <HEAD>
        <TITLE>Using Restricted Access</TITLE>
    </HEAD>    <BODY>
        <H1>Using Restricted Access</H1>
        <%!
            javax.servlet.jsp.JspWriter localOut;            class vehicle
            {
                protected void start()  throws java.io.IOException
                {
                    localOut.println("Starting...<BR>");
                }
            }            class automobile extends vehicle
            {
                public void drive() throws java.io.IOException 
                {
                    localOut.println("Driving...<BR>");
                }
            }
        %>     
        <%
               localOut = out;              out.println("Creating an automobile...<BR>");
            automobile a = new automobile();
            a.start();
            a.drive();
        %>
    </BODY>
</HTML> 
请问 localOut = out;  是什么意思
为什么不能直接用 localOut.println