How to use Abstract Classes in java

Using Abstract Classes

<%!
javax.servlet.jsp.JspWriter localOut;

abstract class a
{
abstract String getText() throws java.io.IOException;

public void printem() throws java.io.IOException
{
localOut.println(getText());
}
}

class b extends a
{
String getText() throws java.io.IOException
{
return "Hello from JSP!";
}
}
%>
<%
localOut = out;

b bObject = new b();

bObject.printem();
%>