Map keySet, values should not be used

I got a warning that I can use ʻentrySet ()` in findbugs even with code that uses only key like ↓.

for(var key : map.keySet()){
    // map.get(key)Processing that uses only key purely without doing such things
}

I interpreted that ʻentrySet () is more efficient if both key and value ** are used, so if only one is used, isn't it related to efficiency? Rather, ʻEntry <K, V> has both key and value, so I think that one of the unnecessary resources is wasted, so I will look at the internal implementation for trade-in.

AbstractMap.java

public Set<K> keySet() {
        Set<K> ks = keySet;
        if (ks == null) {
            ks = new AbstractSet<K>() {
                public Iterator<K> iterator() {
                    return new Iterator<K>() {
                        private Iterator<Entry<K,V>> i = entrySet().iterator();
                        
                        //Abbreviation

                    };
                }
            };
            keySet = ks;
        }
        return ks;
    }

If there is no keySet, it is created and stored in the field, but it can be seen that ʻentrySet (). Iterator () is called to initialize ʻIterator <K>. After all, it seems that keySet () and values () go through ʻentrySet ()`.

In other words, the warning that you should use ʻentrySet ()` to stop thinking, even if you have only one of the key or value, was ** correct **.