When should a for loop be used instead of a while loop?
The golden rule in iteration: everything done with a for loop
can be done with a while loop, BUT not all while loops can be
implemented with a for loop. for-loops are just a short-cut way for
writing a while loop, while an initialization statement, control
statement (when to stop), and a iteration statement (what to do
with the controlling factor after each iteration). = Examples of
for-loops = The most basic use for using for-loops is to do
something a set number of times: for(int k = 0; k < 10; k++); //
this loops runs for 10 times another less common use of the
for-loop is traversing raw listNodes, since it does contain an
initialization(finding the first node), control (as long as there
is a next node), and a iteration statement (get my next node).
i.e.: for(ListNode temp = startingNode; temp != null; temp =
temp.getNext); // this traverses the entire ListNode list and stops
when it has exhausted the list = How to implement for-loops using
while loop = Basically for loops are just short hand for while
loops, any for loop can be converted from: for([initialize];
[control statement]; [iteration]); to [initialize]; while([control
statement]) { //Do something [iteration]; } These two does the
exact same thing. = For When Only while Loop can be used =
while-loops are used when the exiting condition has nothing to do
with the number of loops or a controll variable, maybe you just
want to keep prompting the user for an input until the given input
is valid, like the following example which demands a positive
number: int x = [grab input]; while(x < 0) { // Do code
x = [grab input];
} It is true that, when used as intended, a for loop cannot do
everything a while loop can, however, in reality, for loops are
just as versatile. For example, the above while loop can easily be
rewritten to be a for loop as so:
for(int x = [grab input]; x < 0; x = [grab input]){
// Do Code
}
The above for loop behaves exactly like the while loop in the
previous heading. A better example of a while loop that should not
be a for loop might be:
while(true){
// Do some processing
// Check some condition. If condition is met, break out of
loop.
// Do some more processing.
}
Here, the checking of the condition comes in the middle of the
processing for the while loop, whereas the condition checked in a
for loop is always done at the beginning of the loop. Also, the
"iteration" statement is non-existant and is a factor of processing
done somewhere else in the while loop. Finally, there was no
initialization for this while loop. However, this while loop can
still be written as a for loop:
for(;true;){
// Do some processing
// Check some condition. If condition is met, break out of
loop.
// Do some more processing.
}
As you can see, a for loop is exactly like a while loop if you
leave out the initialization and iteration sections (you still
needs the semicolons, to signify those parts of the for loop are
still there, they just do nothing). However, it is clear that when
you do not need the extra portions of the for loop, why not just
use a while loop?
The basic for loop was extended in Java 5 to make iterating over
arrays and other collections more convenient. See this website for
further explanation:
(http://www.leepoint.net/notes-java/flow/loops/foreach.html)
Steve
Maxine
Vivi
