The JSP Files - Parts 1 to 8: Tagged and Bagged

Do It, Or Else...

In addition to the "if" statement, JSP also offers the "if-else" statement, which allows you to execute different blocks of code depending on whether the expression is evaluated as true or false.

The structure of an "if-else" statement looks like this:

if (condition)        
{        
do this!        
}        
else        
{        
do this!        
}

In this case, if the conditional expression evaluates as false, all statements within the curly braces of the "else" block will be executed. Modifying the example above, we have:

<%!        
// declare temperature variable        
int temp = 50;        
%>        
       
<%        
// check temperature and display output        
if (temp > 30)        
{        
out.println("Man, it's hot out there!");        
}        
else        
{        
out.println("Well, at least it isn't as hot as it could be!"); } %>

In this case, if the first past of the construct fails (temperature is *not* greater than 30), control is transferred to the second part -- the "else" statement -- and the code within the "else" block is executed instead. You can test both possibilities by adjusting the value of the "temp" variable, and viewing the resulting output in your browser.

Cookie-Cutter Code

The "if-else" construct certainly offers a smidgen more flexibility than the basic "if" construct, but still limits you to only two possible courses of action. If your script needs to be capable of handling more than two possibilities, you should reach for the "if-else if-else" construct, which is a happy combination of the two constructs you've just been reading about.

if (first condition is true)        
{        
do this!        
}        
else if (second condition is true)        
{        
do this!        
}        
else if (third condition is true)        
{        
do this!        
}        
       
... and so on ...        
       
else        
{        
do this!        
}

Take a look at it in action:

<%!        
// declare temperature variable        
int temp = 20;        
%>        
       
<%        
// check temperature and display output        
// what happens if temp is less than 25 degrees        
if (temp >= 25)        
{        
out.println("Man, it's hot out there!");        
}        
// what happens if temp is between 25 and 10 degrees        
else if (temp < 25 && temp > 10)        
{        
out.println("Great weather, huh?!");        
}        
// what happens if temp is less than ten degrees        
else if (temp <= 10)        
{        
out.println("Man, it's freezing out there!");        
}        
// this is redundant, included for illustrative purposes        
else        
{        
out.println("Huh? Somebody screwed up out there!");        
}        
%>

In this case, depending on the value of the "temp" variable, the appropriate code branch is executed, thereby making it possible to write scripts which allow for multiple possibilities.

One important point to be noted here: control is transferred to successive "if" branches only if the preceding condition(s) turn out to be false. Or, in English, once a specific conditional expression is satisfied, all subsequent conditional expressions are ignored.

Here's another example, this one using the day of the week to decide which fortune cookie to display. Alter the "day" variable to see a different cookie each time.

<%!        
String day = "Monday";        
String fortune;        
%>        
<%        
// check day and set fortune        
if (day.equals("Monday"))        
{        
fortune = "Adam met Eve and turned over a new leaf.";        
}        
else if (day.equals("Tuesday"))        
{        
fortune = "Always go to other people's funerals, otherwise          
they won't come to yours."; } else if (day.equals("Wednesday"))        
{ fortune = "An unbreakable toy is useful for breaking other toys."; }        
else if (day.equals("Thursday")) { fortune = "Be alert - the          
world needs more lerts."; } else if (day.equals("Friday"))        
{ fortune = "Crime doesn't pay, but the hours are good."; }          
else { fortune = "Sorry, closed on the weekend"; }          
// print output out.println(fortune); %        
>
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