2.27 Jb0230: java oop: flow of control  (Page 6/9)

One author suggests that even the middle clause can be empty, but it isn't obvious to this author how the loop would ever terminate if there is noconditional expression to be evaluated. Perhaps the loop could be terminated by using a break inside the loop, but in that case, you might just as welluse a while loop.

The for-each loop

There is another form of loop structure that is often referred to as a for-each loop. In order to appreciate the benefits of this loop structure, you need to be familiar with Java collections and iterators,both of which are beyond the scope of this module.

As near as I can tell, there is nothing that you can do with the for-each loop that you cannot also do with the conventional for loop described above. Therefore, I rarely use it. You can find a description ofthe for-each loop on this Oracle website .

I don't plan to discuss it further in this module. However, before you go for a job interview, you should probably do some online research and learn about itbecause an interviewer could use a question about the for-each loop to trip you up in the Q and A portion of the interview.

The do-while loop

The do-while loop is another implementation of the loop pillar mentioned earlier . However, it differs from the while loop and the for loop in one important respect; it is an exit-condition loop.

An exit-condition loop

Java provides an exit-condition loop having the syntax shown in Figure 6 .

Behavior

The statements in the body of the loop continue to be executed for as long as the conditional expression evaluates to true.An exit-condition loop guarantees that the body of the loop will be executed at least one time, even if the conditional expressionevaluates to false the first time it is tested.

The break and continue statements

General behavior

Although some authors suggest that the break and continue statements provide an alternative to the infamous goto statement of earlier programming languages, it appears that the behaviors of the labeled break and labeled continue statements are muchmore restrictive than a general goto .

Unlabeled break and continue

The break and continue statements are supported in both labeled and unlabeled form.

First consider the behavior of break and continue in their unlabeled configuration.

Use of a break statement

The break statement can be used in a switch statement or in a loop. When encountered in a switch statement, breakcauses control to be passed to the next statement outside the innermost enclosing switch statement.

When break is encountered in a loop, it causes control to be passed to the next statement outside the innermost enclosing loop.

As you will see later, labeled break statements can be used to pass control to the next statement following switch or loop statementsbeyond the innermost switch or loop statement when those statements are nested.

Use of a continue statement

The continue statement cannot be used in a switch statement, but can be used inside a loop.