Strange control statement in Collection class

Question

I came across this code in Java API Collection class. Does it work like switch statement ? How is this idiom called ?

public static int indexOfSubList(List<?> source, List<?> target) { int sourceSize = source.size(); int targetSize = target.size(); int maxCandidate = sourceSize - targetSize; if (sourceSize < INDEXOFSUBLIST_THRESHOLD || (source instanceof RandomAccess&&target instanceof RandomAccess)) { nextCand: for (int candidate = 0; candidate <= maxCandidate; candidate++) { for (int i=0, j=candidate; i<targetSize; i++, j++) if (!eq(target.get(i), source.get(j))) continue nextCand; // Element mismatch, try next cand return candidate; // All elements of candidate matched target } } else { // Iterator version of above algorithm ListIterator<?> si = source.listIterator(); nextCand: for (int candidate = 0; candidate <= maxCandidate; candidate++) { ListIterator<?> ti = target.listIterator(); for (int i=0; i<targetSize; i++) { if (!eq(ti.next(), si.next())) { // Back up source iterator to next candidate for (int j=0; j<i; j++) si.previous(); continue nextCand; } } return candidate; } } return -1; // No candidate matched the target }

Does what work like switch? You've presented a lot of code. Are you really just interested in the labeled continue statements? — Jon Skeet
– Jon Skeet, Commented Jan 4, 2013 at 13:56
@JonSkeet I think he is referring to labels and labelled continues — Mark Rotteveel
– Mark Rotteveel, Commented Jan 4, 2013 at 13:58

Mob · Accepted Answer · 2013-01-04 14:04:34Z

5

No, its just a labeled break/continue. see here:

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/branch.html

Java allows using label as break/continue targets. By default a break/continue will affect the inner-most loop its in, but using labels you can break out of outer loops.

edited Jan 4, 2013 at 14:04

Mob

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answered Jan 4, 2013 at 13:56

radai

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3 Comments

radai Over a year ago

its rarely useful, and makes some people cross themselves and call you the devil for using gotos :-)

xagyg Over a year ago

In 25 years of programming I have used a label (in C) once. Never needed it yet in Java (in 15 years)! Try to avoid it if possible.

radai Over a year ago

i used it for the 1st time about 2 weeks after taking up java and got into a heated argument with my then-team-lead. if you really need to break/continue out of an inner loop, say 3+ loops deep it both perfors better and looks better (the aternative involves a boolean flag and a lot of noise checking it). of course if you have 3+ loops one inside the other there's probably something else wrong with your code ...

NPE · Accepted Answer · 2013-01-04 13:58:14Z

Assuming you're referring to nextCand: and continue nextCand;, it's simply a way to continue to the next iteration of the outer loop from within the inner loop.

A simple continue would continue the inner loop instead.

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