Example2.java

class Example2 {
    private final Database database;

    Example2(Database database) {
        this.database = database;
    }

    boolean activateUser(Long userId) {
        User user = database.findUser(userId);
        if (user != null && !user.isActive()) {
            database.activateUser(userId);
            return true;
        } else {
            return false;
        }
    }
}

interface Database {
    User findUser(Long id);

    void activateUser(Long id);
}

interface User {
    boolean isActive();
}