Re: LinkedHashMap - get latest key?

Andreas Leitgeb <avl@auth.logic.tuwien.ac.at> wrote:


If you don't have to remove objects from the map, or you can live with
remove being O( n ) when it's the latest added element that's removed,
you can just subclass LinkedHashMap like below. (Warning: the code
hasn't been tested, just written. Caveat emptor.)

If you frequently pop the most recently added element from the map,
though, this approach is useless.

public class LinkedHashMapHack<K, V> extends LinkedHashMap<K, V> {

    private K mostRecentKey;
    private V mostRecentValue;

    public Map.Entry<K, V> getMostRecentEntry( Object key ) {
        Map.Entry<K, V> mostRecentEntry = new AbstractMap.SimpleImmutableEntry<>( mostRecentKey, mostRecentValue );
        return mostRecentEntry;
    }

    @Override
    public void clear() {
        super.clear();
        mostRecentKey = null;
        mostRecentValue = null;
    }

    @Override
    public V put( K key, V value ) {
        V previousAtKey = super.put( key, value );
        mostRecentKey = key;
        mostRecentValue = value;
        return previousAtKey;
    }

    @Override
    public V remove( Object key ) {
        V removed = super.remove( key );

        if( size() == 0 ) {
            mostRecentKey = null;
            mostRecentValue = null;
        } else if( key.equals( mostRecentKey ) ) {
            findNewMostRecentKeyAndValue();
        }

        return removed;
    }

    private void findNewMostRecentKeyAndValue() {
        Map.Entry<K, V> lastEntry = null;
        for( Map.Entry<K, V> entry : super.entrySet() ) {
            lastEntry = entry;
        }

        mostRecentKey = lastEntry.getKey();
        mostRecentValue = lastEntry.getValue();
    }
  }

--
Leif Roar Moldskred