Jump Statements and Loop Variations: break, continue and Labels

Hello students, welcome to Kwickprep. A break inside two loops leaves only the inner one. So how do you jump out of both at once? Today we trace break and continue step by step, and learn labels for nested loops. We will also meet infinite loops, empty loops, and the loop variations that board papers love.

A jump statement moves control to another place, instead of the next line. Break stops the loop completely, and control goes to the line after the loop. Continue skips only the rest of the current iteration, and the loop carries on with the next one. We usually put them inside an if, so they act only in a special case.

Let us trace it. When i is one, i equals three is false, so it prints one. When i is two, it prints two. When i is three, the condition is true, and break ends the loop at once. Four and five never run, and control goes to the line after the loop, which prints Done.

Now the same loop with continue. When i is one and two, they print as before. When i is three, continue skips the print, but the loop does not end. In a for loop, continue jumps to the update, so i becomes four. Four and five print, and then Done.

Here is the difference in one table. After break, the loop ends, but after continue, the loop goes on. Break jumps to the line after the loop, while continue jumps to the next iteration. Break is also used to end a switch, and continue only ever affects a loop.

A label is a name followed by a colon, written just before a loop. Here the outer loop is labelled outer. A plain break would leave only the inner loop. But break outer leaves both loops at once. So only one, one prints, and the program ends.

Pause and predict. This time it says continue outer. When j reaches two, Java skips the rest of the inner loop, and starts the next iteration of the outer loop. So for each i, only j equals one prints. The output is one one, two one, and three one.

An infinite loop is a loop whose condition never becomes false, so it never stops by itself. For with two semicolons and nothing else has no condition, so Java treats it as always true. While true is also always true, and we stop it from inside with a break. But a while loop that forgets to update i is a bug, and the program hangs.

An empty loop has no body, only a semicolon. Older textbooks call it a time delay loop, because it only counts. Here i is declared outside, so we can print it later. The loop runs while i is five or less, and stops when i becomes six. So it prints six, just once.

Board papers often change the normal loop, so learn these variations. A loop can count down, using i minus minus. It can move in steps, like i plus equals two, which gives one, three, five, seven and nine. It can use two variables, separated by a comma. And any of the three parts can be left out, which makes a for loop behave like a while loop.

Here is a typical board question. How many times does the loop run, and what prints? Trace it. First i is one and j is ten. Then i is three and j is eight, then i is five and j is six. Next i is seven and j is four, so i less than j is false. The loop ran three times, and it prints seven four.

Let us recap. Break ends the loop, while continue skips only the current iteration. A label lets break or continue act on an outer loop. For with two semicolons and while true are infinite loops. A loop that ends in a semicolon has an empty body. And to answer variation questions, write down every value of the variables, step by step.