defaultdict in java

DefaultHashMap.java

public class DefaultHashMap<K, V> extends HashMap<K, V> {

    private final Class<V> cls;

    public DefaultHashMap(Class factory) {
        this.cls = factory;
    }

    @Override
    public V get(Object key) {
        V value = super.get(key);
        if (value == null) {
            try {
                value = cls.newInstance();
            } catch (Exception e) {
                e.printStackTrace();
            }
            this.put((K) key, value);
        }
        return value;
    }

    public static void main(String[] args) {
        Map<String, List<String>> dm = new DefaultHashMap<String, List<String>>(ArrayList.class);
        dm.get("missing").add("roger");
        dm.get("missing").add("roger2");
        System.out.println(dm.get("missing"));
        System.out.println(dm.get("missing2"));
    }

}