The JSP Files (part 2): Attack Of The Killer Fortune Cookies

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.

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

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February 22, 2001

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With a little bit of luck, our introductory article on JSP left you so excited that you spent the last few days eagerly practicing variable names and letting your friends know how much smarter you are than them. And this week, we're going to help you cement your reputation still further, by giving you a crash course in JSP's conditional statements and loops.

Make sure you're strapped in tight - this is gonna be one hell of a ride!{mospagebreak title=Adding It All Up} You'll remember how, in the first part of this tutorial, we used the + operator to add numbers and strings together. And just as you have the + operator for addition, JSP comes with a bunch of other arithmetic operators designed to simplify the task of performing mathematical operations.

The following example demonstrates the important arithmetic operators available in JSP:

<html>
<head>
</head>
<body>
<%!
// declare variables
int alpha = 25;
int beta = 5;
int sum, difference, product, quotient, remainder;
%>
<%
// perform operations
out.println("The sum of " + alpha + " and " + beta + " is " + (alpha +
beta) + "<br>");
out.println("The difference of " + alpha + " and " + beta + " is " + (alpha
- beta) + "<br>");
out.println("The product of " + alpha + " and " + beta + " is " + (alpha *
beta) + "<br>");
out.println("The quotient after division of " + alpha + " and " + beta + "
is " + (alpha / beta) + "<br>");
out.println("The remainder after division of " + alpha + " and " + beta + "
is " + (alpha % beta) + "<br>");
%>
</body>
</html>

And here's the output:


The sum of 25 and 5 is 30
The difference of 25 and 5 is 20
The product of 25 and 5 is 125
The quotient after division of 25 and 5 is 5
The remainder after division of 25 and 5 is 0

As with all other programming languages, division and multiplication take precedence over addition and subtraction, although parentheses can be used to give a particular operation greater precedence. For example,

<%
out.println(10 + 2 * 4);
%>
<hr noshade size=1 color=#cccccc></pre></blockquote><br>
returns 18, while<br>
<blockquote><pre><hr noshade size=1 color=#cccccc>
<%
out.println((10 + 2) * 4);
%>

returns 48.

In addition to these operators, JSP comes with the very useful auto-increment [++] and auto-decrement [--] operators, which you'll see a lot of in the next article. The auto-increment operator increments the value of the variable to which it is applied by 1, while the auto-decrement operator does the opposite. Here's an example:

<%!
int x = 99;
%>
<%
// x = 99
out.println("Before increment, x = " + x + "<br>");
x++;
// x = 100
out.println("After increment, x = " + x);
%>

JSP also comes with a bunch of comparison operators, whose sole raison d'etre is to evaluate expressions and determine if they are true or false. The following table should make this clearer.

Assume x=4 and y=10

Operator	What It Means	Expression	Result
==	is equal to	x == y	False
!=	is not equal to	x != y	True
>	is greater than	x > y	False
<	is less than	x < y	True
>=	is greater than or equal to	x >= y	False
<=	is less than or equal to	x <= y	True