when will hashcode be calculated [closed]

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I want to put an object that has been created for a while into a hashmap, and I want it to store according to the current state of the objects.

So I wonder when the hashcode of this object is calculated: when it is created or it is put into the map. And if it is the first situation, how to store the current state.

Thanks a lot.

Edit: I actually mean store it according to the state when insert it into the map. Sorry to mislead.

Answer 1

An object's hashcode is retrieved whenever any code calls the object's hashCode() method (such as a collection, container or any other method).

All the classes inherit a basic hash scheme from the fundamental base class java.lang.Object, but instead many override this to provide a hash function that better handles their specific data. Classes which provide their own implementation must override the object method public int hashCode().

Ref: java hashCode()

Answer 2

Thanks to the reminder of David Wallace, I found this code in hashmap:

public V put(K key, V value) {
    if (key == null)
        return putForNullKey(value);
    int hash = hash(key.hashCode());
    int i = indexFor(hash, table.length);
    for (Entry<K,V> e = table[i]; e != null; e = e.next) {
        Object k;
        if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
            V oldValue = e.value;
            e.value = value;
            e.recordAccess(this);
            return oldValue;
        }
    }

And it indeed invoke the hashCode() when put it into hashmap.