Switching Things Around - Java

The second part of our introductory JSP tutorial discussesarithmetic, logical and comparison operators, together with simple examplesand illustrations. You'll also learn the basics of JSP's numerousconditional expressions, including the "if", "if-else" and "switch"statements, and find out a little more about the String object.

TABLE OF CONTENTS:

By: Vikram Vaswani and Harish Kamath, (c) Melonfire

Poor Best

Rating:

/ 4

February 22, 2001

print this article

SEARCH DEV SHED

TOOLS YOU CAN USE

Finally, JSP rounds out its conditional expressions with the "switch" statement, which offers an alternative method of transferring control from one program block to another. Here's what it looks like:

switch (decision-variable)
{
case first_condition_is true:
do this!
case second_condition_is true:
do this!
case third_condition_is true:
do this!
... and so on...
default:
do this by default!
}

The "switch" statement can best be demonstrated by rewriting the previous example using "switch" instead of "if-else if-else".

<%!
int dayOfWeek = 3;
String fortune;
%>
<%
// the decision variable here is the day chosen by the user
switch (dayOfWeek)
{
// first case
case 1:
fortune = "Adam met Eve and turned over a new leaf.";
break;
// second case
case 2:
fortune = "Always go to other people's funerals, otherwise they
won't come to yours.";
break;
case 3:
fortune = "An unbreakable toy is useful for breaking other toys.";
break;
case 4:
fortune = "Be alert - the world needs more lerts.";
break;
case 5:
fortune = "Crime doesn't pay, but the hours are good.";
break;
// if none of them match...
default:
fortune = "Sorry, closed on the weekend";
break;
}
// print output
out.println(fortune);
%>

The first thing you'll notice is that the "day" variable from the previous example has been converted to a numeric "dayOfWeek" variable - this is because the "switch" construct only works when the decision variable is an integer.

There are also a couple of important keywords here: the "break" keyword is used to break out of the "switch" statement block and move immediately to the lines following it, while the "default" keyword is used to execute a default set of statements when the variable passed to "switch" does not satisfy any of the conditions listed within the block.

And that's about it. You now know enough about JSP's conditional statements to begin writing simple programs - so go practice! And come back for the next issue, when we'll be talking about loops, demonstrating other String object methods, and even taking a quick look at the new Response object.