how to write a hashcode method for a hashmap in java code example

Example: java hashcode

@Overridepublic int hashCode() {    int hash = 7;    hash = 31 * hash + (int) id;    hash = 31 * hash + (name == null ? 0 : name.hashCode());    hash = 31 * hash + (email == null ? 0 : email.hashCode());    return hash;}