HashMap lookup fails due to missing hashCode

import java.util.HashMap;
import java.util.Map;
import java.util.Objects;

class UserKey {
    String username;
    UserKey(String u) { this.username = u; }
    
    // Overrides equals but NOT hashCode!
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        UserKey userKey = (UserKey) o;
        return Objects.equals(username, userKey.username);
    }
}

public class Main {
    public static int cacheUserRecord(String username) {
        Map<UserKey, Integer> map = new HashMap<>();
        map.put(new UserKey(username), 100);
        // Lookup creates new UserKey instance with different default identity hashCode
        Integer val = map.get(new UserKey(username));
        return val != null ? val : -1;
    }

    public static void main(String[] args) {
        System.out.println(cacheUserRecord("Alice"));
    }
}