Java Reference
In-Depth Information
This statement defines and initializes a counter but we have not defined a counter update. Because the counter
is never updated, the condition will always be true and the println statement will execute endlessly. What we have
created is called an
endless
(or
infinite
)
loop
. Do I need to tell you that this is a bad thing?
If you were to run the application now, it would run until you either terminated it from the Console view or
closed RAD.
We definitely need to update the ctr so that it reaches 10 and the loop is ended.
6.
After the println statement, add the following:
ctr = ctr + 1;
7.
Save and run LoopTestApp.
The results will be the same as the
for
loop: 10 lines with the counter (ctr) value followed by the word “little.”
8.
Comment out the
while
loop (don't comment out the ctr definition).
9.
Add the following
do while
loop after the ctr definition:
do
{
System.out.println(ctr + " little");
ctr = ctr + 1;
}
while
(ctr <= 10);
10.
Save and run LoopTestApp.
Once again, the same results will be displayed. You may be wondering why there are three methods for defining
loops. Unfortunately, you do not have enough programming experience to appreciate the subtle differences between
the three methods. When we change our application to access a database, your appreciation of loops will grow
considerably.
Tutorial: More About Iteration
The keywords
break
and
continue
are often used with loops. A break statement ends the loop. This means that the
first statement following the loop will be executed. A continue statement bypasses any remaining statements within
the loop but does not end the loop. A
continue
statement in a
for
loop results in the counter being updated, and the
next iteration is performed. In
while
and
do while
loops, a continue forces the JVM to perform the condition test and
either perform another iteration or end the loop.
Both keywords are usually used within an
if
statement to stop looping or to skip the remaining statements in one
iteration of a loop. Let's try to skip the “5 little” text.
1.
In LoopTestApp, comment out the
do while
loop (don't comment out the ctr definition).
2.
Add the following
do while
loop and run the application:
do
{
System.out.println(ctr + " little");
if
(ctr == 5) {
break
;
}
ctr = ctr + 1;
}
while
(ctr <= 10);
