iterating over and removing from a map

Here is a code sample to use the iterator in a for loop to remove the entry.

Map<String, String> map = new HashMap<String, String>() {
  {
    put("test", "test123");
    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();
    }
}

Use a real iterator.

Iterator<Object> it = map.keySet().iterator();

while (it.hasNext())
{
  it.next();
  if (something)
    it.remove();
 }

Actually, you might need to iterate over the entrySet() instead of the keySet() to make that work.

You have to use Iterator to safely remove element while traversing a map.

I agree with Paul Tomblin. I usually use the keyset's iterator, and then base my condition off the value for that key:

Iterator<Integer> it = map.keySet().iterator();
while(it.hasNext()) {
    Integer key = it.next();
    Object val = map.get(key);
    if (val.shouldBeRemoved()) {
        it.remove();
    }
}

An alternative, more verbose way

List<SomeObject> toRemove = new ArrayList<SomeObject>();
for (SomeObject key: map.keySet()) {
    if (something) {
        toRemove.add(key);
    }
}

for (SomeObject key: toRemove) {
    map.remove(key);
}

Maybe you can iterate over the map looking for the keys to remove and storing them in a separate collection. Then remove the collection of keys from the map. Modifying the map while iterating is usually frowned upon. This idea may be suspect if the map is very large.