Reset all values in hashmap without iterating?

Question

I am trying reset all values in a HashMap to some default value if a condition fails.

Currently i am doing this by iterating over all the keys and individually resetting the values.
Is there any possible way to set a same value to all the keys without iterating?

Something like:

hm.putAll("some val")  //hm is hashmap object

Answer 1

You can't avoid iterating but if you're using java-8, you could use the replaceAll method which will do that for you.

Apply the specified function to each entry in this map, replacing each entry's value with the result of calling the function's Function#map method with the current entry's key and value.

m.replaceAll((k,v) -> yourDefaultValue);

Basically it iterates through each node of the table the map holds and affect the return value of the function for each value.

@Override
public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
    Node<K,V>[] tab;
    if (function == null)
        throw new NullPointerException();
    if (size > 0 && (tab = table) != null) {
        int mc = modCount;
        for (int i = 0; i < tab.length; ++i) {
            for (Node<K,V> e = tab[i]; e != null; e = e.next) {
                e.value = function.apply(e.key, e.value); //<-- here
            }
        }
        if (modCount != mc)
            throw new ConcurrentModificationException();
    }
}

Example:

public static void main (String[] args){ 
    Map<String, Integer> m = new HashMap<>();
    m.put("1",1);
    m.put("2",2);

    System.out.println(m);
    m.replaceAll((k,v) -> null);
    System.out.println(m);
}

Output:

{1=1, 2=2}
{1=null, 2=null}