CODEWITHSUNDEEP
java
neo
neo

Reputation: 2471

HashMap how to find out "extra" keys and remove them

Suppose I have a Hashmap object myMap and it contains a set of keys and values,

key1, value1
key2, value2
...
...

let's say I have 30 keys in total.

Now I am getting a list of keys: key1, key2...., say there are 28.

What is the best way to check myMap object and remove keys that are NOT in my list of keys? Do I have to iterate thru the hashmap keyset and compare each one in the list?

thanks.

Upvotes: 3

Views: 346

Answers (2)

Fritz
Fritz

Reputation: 10055

Use the containsKey method for each key you have, and if the method returns false, remove it. Another option is to use Map#keySet#retainAll.

Upvotes: 2

rgettman
rgettman

Reputation: 178303

Get the set of keys from the map. The set is backed by the map. Then call retainAll on it.

Set<String> keys = myMap.keySet();
keys.retainAll(keyList);

Here's the documentation on the keySet method.

Here's the documentation on the retainAll method.

Upvotes: 6

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