Читать книгу OCP Oracle Certified Professional Java SE 17 Developer Study Guide - Jeanne Boyarsky - Страница 209

Let's now extend our discussion of advanced loop control with the continue statement, a statement that causes flow to finish the execution of the current loop iteration, as shown in Figure 3.10.

FIGURE 3.10 The structure of a continue statement

You may notice that the syntax of the continue statement mirrors that of the break statement. In fact, the statements are identical in how they are used, but with different results. While the break statement transfers control to the enclosing statement, the continue statement transfers control to the boolean expression that determines if the loop should continue. In other words, it ends the current iteration of the loop. Also, like the break statement, the continue statement is applied to the nearest inner loop under execution, using optional label statements to override this behavior.

Let's take a look at an example. Imagine we have a zookeeper who is supposed to clean the first leopard in each of four stables but skip stable b entirely.

1: public class CleaningSchedule { 2: public static void main(String[] args) { 3: CLEANING: for(char stables = 'a'; stables<='d'; stables++) { 4: for(int leopard = 1; leopard<4; leopard++) { 5: if(stables=='b' || leopard==2) { 6: continue CLEANING; 7: } 8: System.out.println("Cleaning: "+stables+","+leopard); 9: } } } }

With the structure as defined, the loop will return control to the parent loop any time the first value is b or the second value is 2. On the first, third, and fourth executions of the outer loop, the inner loop prints a statement exactly once and then exits on the next inner loop when leopard is 2. On the second execution of the outer loop, the inner loop immediately exits without printing anything since b is encountered right away. The following is printed:

Cleaning: a,1 Cleaning: c,1 Cleaning: d,1

Now, imagine we remove the CLEANING label in the continue statement so that control is returned to the inner loop instead of the outer. Line 6 becomes the following:

6: continue;

This corresponds to the zookeeper cleaning all leopards except those labeled 2 or in stable b. The output is then the following:

Cleaning: a,1 Cleaning: a,3 Cleaning: c,1 Cleaning: c,3 Cleaning: d,1 Cleaning: d,3

Finally, if we remove the continue statement and the associated if statement altogether by removing lines 5–7, we arrive at a structure that outputs all the values, such as this:

Cleaning: a,1 Cleaning: a,2 Cleaning: a,3 Cleaning: b,1 Cleaning: b,2 Cleaning: b,3 Cleaning: c,1 Cleaning: c,2 Cleaning: c,3 Cleaning: d,1 Cleaning: d,2 Cleaning: d,3