Are String hashCode in java pre-computed?

Question

in Java when I say.

String str= "abcd";
str.hashCode(); 

My question is When is Hashcode calculated? @ line 1 or @ line 2?

I am assuming , that hashcode is pre-computed. Whenever string is updated hashcode would also 'perhaps' update.

or its the other way i.e. every time you call str.hashCode() java computes its using the formula that's described here.

Consistency of hashCode() on a Java string

Answer 1

Strings can't be updated since they're immutable, and the value is cached after it's computed once:

public int hashCode() {
        int h = hash;
        if (h == 0 && value.length > 0) {
            char val[] = value;

            for (int i = 0; i < value.length; i++) {
                h = 31 * h + val[i];
            }
            hash = h;
        }
        return h;
    }

Answer 2

You cannot "update" a string. Strings are immutable. When you "change" a string instance, you actually get a new string instance.