BrewlearnLabeled break & continue in Java
Exiting nested loops with labels.
Name your loop
Put a label (a name followed by a colon) in front of a loop. Then **break label;** exits that whole labeled loop, however deeply nested you are.
outer:
for (int r = 0; r < 3; r++) {
for (int c = 0; c < 3; c++) {
if (grid[r][c] == 0) break outer;
}
}
// break outer lands hereYour turn
Which pair is found first?
int found = -1;
search: for (int i = 1; i <= 4; i++) {
for (int j = 1; j <= 4; j++) {
if (i * j == 12) {
found = i * 10 + j;
break search;
}
}
}
System.out.println(found);3443-112
Show the answer
Rows are searched in order, so i = 3, j = 4 is the first pair with a product of 12, giving 34. break search then leaves both loops, so 4 x 3 is never reached.
continue with a label
**continue label; abandons the current inner loop and jumps to the next iteration of the labeled loop**. It's like saying "this row is done, next row please".
rows:
for (int r = 0; r < 3; r++) {
for (int c = 0; c < 3; c++) {
if (bad(r, c)) continue rows;
use(r, c);
}
}Trace it
What prints?
outer:
for (int r = 0; r < 3; r++) {
for (int c = 0; c < 3; c++) {
if (c == 1) continue outer;
System.out.print(r + "" + c + " ");
}
}00 10 2000 01 10 11 20 210001 11 21
Show the answer
In every row, as soon as c reaches 1, continue outer abandons the rest of that row and starts the next r. So each row prints only its c = 0 pair.
continue needs a loop
break label; may target any labeled statement, even a plain block. But continue label; must name a loop: a labeled block has no "next iteration". The compiler says not a loop label. And labels aren't goto: you can only jump *out of* statements you're inside.
block: {
if (done) break block; // ok
continue block; // error: not a loop label
}Escaping two loops
for (...) {
for (...) {
break; break;
}
}The first break leaves; the second is unreachable code, so it doesn't even compile.
search:
for (...) {
for (...) {
break search;
}
}Alternatives without labels: a boolean flag the outer loop checks, or move the loops into a method and return.
In real projects
Labels are rare in production code but perfectly legitimate for grid searches and parsers. Many teams prefer moving nested loops into a small method and using return: it's often clearer, and the method name explains what the search does.
Key takeaways
- Syntax: outer: for (...) { for (...) { break outer; } }
- break label exits the labeled statement completely
- continue label must name a loop
- Labels aren't goto: you can only jump out of statements you're inside
A line like http://example.com placed right before a statement in a method compiles! http: is a label, and //example.com is just a comment.
Practice questions
What does this print?
int found = -1;
search: for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= 3; j++) {
if (i * j == 6) {
found = i * 10 + j;
break search;
}
}
}
System.out.println(found);- 32
- -1
- 6
- 23
Check your answer
23. The first pair with i * j == 6 is i = 2, j = 3, giving 23. break search then leaves both loops, so i = 3, j = 2 is never reached.
Without labels, what's the usual way to stop two nested loops at once?
- Write break; break; on the same line
- Use continue in the inner loop
- Use a boolean flag checked by the outer loop, or move the loops into a method and return
- Set the outer loop's variable to null
Check your answer
Use a boolean flag checked by the outer loop, or move the loops into a method and return. A flag or an early return both work. break; break; doesn't: the second break is unreachable code and won't compile.