ConcurrentModificationException with LinkedHashMap

Question

Not sure what is triggering a java.util.ConcurrentModificationException when I iterate over the LinkedHashMap structure in the code below. Using the

Answer 1

Your code

for(String key : lru_cache.keySet()){
    System.out.println(lru_cache.get(key));
}

Actually compiles to:

Iterator it = lru_cache.keySet().iterator();
while (it.hasNext()) {
    String key = it.next();
    System.out.println(lru_cache.get(key));
}

Next, your LRU cache shrinks itself to MAX_SIZE elements not when calling set(), but when calling get() - above answers explain why.

Thus we have following behavior:

• new iterator created to iterate over lru_cache.keySet() collection
• lru_cache.get() called to extract element from your cache
• get() invocation truncates lru_cache to MAX_SIZE elements (in your case 3)
• iterator it becomes invalid due to collection modification and throws on next iteration.