Question

Just found a bug in this code :

    for(String link : tempList1){
        if(!tempList2.contains(link));{
            listToPopulate.add(link);
        }
    }

The ‘;’ at the end of if(!tempList2.contains(link)) causes the condition to evaluate to true, even though it should be false. Why is this occurring ?

Fix is to just remove the ‘;’

Answer 1

The compiler sees an if condition followed by a stand-alone block. With standard indenting, it would look like this:

for(String link : tempList1){
    if(!tempList2.contains(link))
        ;  // ; is a no-op statement.
    {
        listToPopulate.add(link);
    }
}

http://en.wikipedia.org/wiki/NOP#NOP_code

The simplest possible statement in C that behaves like a NOP is the so called null statement, which is just a semi-colon in a context requiring a statement.

Java inherited this syntax from C.