Is the following code safe? Assume its single-threaded.
for(String s : set){ set.remove(s); set.remove(randomElementFromSet()); } I'm pretty sure this should be fine, but I want to double check that I run no risk of iterating over an element that has already been removed.
Also if possible please provide reference so I can look it up next time.
Have you tried it? You would get ConcurrentModificationException.
One safe way to remove elements from a Collection while iterating over it is by using an Iterator explicitly:
for(Iterator<String> iter = set.iterator(); iter.hasNext();) { String s = iter.next(); iter.remove(); } You should not filter a collection using a for-each loop as you can get a ConcurrentModificationException.
To do it correctly you can use an Iterator, or removeIf. Both of these pieces of code print [Foo].
Approach using Iterator:
Set<String> set = new HashSet<String>(Arrays.asList("Foo", "Bar", "Baz")); for (Iterator<String> i = set.iterator(); i.hasNext();) if (i.next().contains("B")) i.remove(); System.out.println(set); Approach using removeIf (Java 8):
Set<String> set = new HashSet<>(Arrays.asList("Foo", "Bar", "Baz")); set.removeIf(str -> str.contains("B")); System.out.println(set); 