HashMap: iterating the key-value pairs in random order

Question

I have a HashMap and I\'d like to iterate they key-value pairs in a different random order each time i get the iterator. Conceptually I\'d like to \"shuffle\" the map before

Answer 1

Actually you do not need to shuffle at all:
Just draw a random index in an array of keys and remove the key by overwritting with the last:

public class RandomMapIterator implements Iterator {

private final Map map;
private final K[] keys;

private int keysCount;

@SuppressWarnings("unchecked")
public RandomMapIterator(Map map) {
    this.map = map;
    this.keys = (K[]) map.keySet().toArray();
    this.keysCount = keys.length;
}

@Override
public boolean hasNext() {
    return keysCount!=0;
}

@Override
public V next() {
    int index = nextIndex();
    K key = keys[index];
    keys[index] = keys[--keysCount];
    return map.get(key);
}

protected int nextIndex() {
    return (int)(Math.random() * keysCount);
}

@Override
public void remove() {
    throw new UnsupportedOperationException();
}

}