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How to Safely Remove Entries from a Concurrent Map While Iterating?
- Patricia ArquetteOriginal
- 2024-11-12 10:21:02404browse
Iterating Over and Removing from a Concurrent Map
When modifying a map during iteration, it's crucial to avoid ConcurrentModificationException errors. The classic approach of using for (Object key : map.keySet()) fails because map modifications can occur during the loop.
A common workaround is to copy the key set into a new collection, as seen in for (Object key : new ArrayList
A better solution involves using an iterator to remove map entries. Here's an example:
Map<String, String> map = new HashMap<>();
map.put("test", "test123");
map.put("test2", "test456");
for(Iterator<Map.Entry<String, String>> it = map.entrySet().iterator(); it.hasNext(); ) {
Map.Entry<String, String> entry = it.next();
if(entry.getKey().equals("test")) {
it.remove();
}
}
This code uses an iterator to safely remove entries from the map. The iterator's remove() method removes the current entry, allowing for safe and efficient map modifications during iteration.
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