Java Reference
In-Depth Information
loop and the while keyword to mark the end and introduce the loop condition.
Also, unlike the while loop, the do loop is terminated with a semicolon. This is
because the do loop ends with the loop condition rather than simply ending with a
curly brace that marks the end of the loop body. The following do loop prints the
same output as the while loop just discussed:
a x
int count = 0 ;
do {
System . out . println ( count );
count ++;
} while ( count < 10 );
The do loop is much less commonly used than its while cousin because, in practice,
it is unusual to encounter a situation where you are sure you always want a loop to
execute at least once.
The for Statement
The for statement provides a looping construct that is often more convenient than
the while and do loops. The for statement takes advantage of a common looping
pattern. Most loops have a counter, or state variable of some kind, that is initialized
before the loop starts, tested to determine whether to execute the loop body, and
then incremented or updated somehow at the end of the loop body before the test
expression is evaluated again. The initialization, test, and update steps are the three
crucial manipulations of a loop variable, and the for statement makes these three
steps an explicit part of the loop syntax:
for ( initialize ; test ; update ) {
This for loop is basically equivalent to the following while loop:
initialize ;
while ( test ) {
statement ;
update ;
Placing the initialize , test , and update expressions at the top of a for loop
makes it especially easy to understand what the loop is doing, and it prevents mis‐
takes such as forgetting to initialize or update the loop variable. The interpreter dis‐
cards the values of the initialize and update expressions, so to be useful, these
expressions must have side effects. initialize is typically an assignment expression
while update is usually an increment, decrement, or some other assignment.
The following for loop prints the numbers 0 to 9, just as the previous while and do
loops have done:
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