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These methods are usually overridden when you want to use objects of that type as keys in data structures like hashtables.
Whenever overriding the equals method is recommended to also override the hashCode method. That is because there must be a relationship between these two methods: equal objects must have equal hash codes, but non-equal objects can have the same hash code.

If the methods are not overridden , then using them as keys in a hashtable is practically impossible (inefficient). By default equals returns true if the two reference variables refer to the same object , and hashCode returns different hash codes for different objects.

Failure to override one of them while overriding other will result in inconsistent working of hash-based collections..

@Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj == null || obj.getClass() != this.getClass()) {
            return false;
        }

        Person guest = (Person) obj;
        return id == guest.id;
    }
    
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((firstName == null) ? 0 : firstName.hashCode());
        result = prime * result + id;
        result = prime * result
                + ((lastName == null) ? 0 : lastName.hashCode());
        return result;
    }

public boolean equals(Object object) {
return this == object;
}

public int hashCode() {
return VMMemoryManager.getIdentityHashCode(this);
}

@techpanja: I think you should add instance of check before casting

Person guest = (Person) obj;