The JSP Files (part 2): Attack Of The Killer Fortune Cookies (
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The second part of our introductory JSP tutorial discusses
arithmetic, logical and comparison operators, together with simple examples
and illustrations. You'll also learn the basics of JSP's numerous
conditional expressions, including the "if", "if-else" and "switch"
statements, and find out a little more about the String object.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 |
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