// 錯(cuò)誤示范！?
public void processUser(Optional user) {
    // ...
}

// 沒(méi)必要！?
Optional> names = Optional.of(Arrays.asList("A", "B"));

// 錯(cuò)誤示范！?
class User {
    private Optional name; // 不要這樣做！
}

public String getEmployeeManagerName(Employee employee) {
    if (employee != null) {
        Department dept = employee.getDepartment();
        if (dept != null) {
            Employee manager = dept.getManager();
            if (manager != null) {
                return manager.getName();
            }
        }
    }
    return "無(wú)經(jīng)理";
}

public String getEmployeeManagerName(Employee employee) {
    return Optional.ofNullable(employee)
        .map(Employee::getDepartment)
        .map(Department::getManager)
        .map(Employee::getName)
        .orElse("無(wú)經(jīng)理");
}

public List getAllManagerNames(List employees) {
    return employees.stream()
        .map(Employee::getDepartment)
        .filter(Objects::nonNull)
        .map(Department::getManager)
        .filter(Objects::nonNull)
        .map(Employee::getName)
        .filter(Objects::nonNull)
        .collect(Collectors.toList());
}

public List getAllManagerNames(List employees) {
    return employees.stream()
        .map(Employee::getDepartment)
        .flatMap(dept -> Optional.ofNullable(dept).stream())
        .map(Department::getManager)
        .flatMap(manager -> Optional.ofNullable(manager).stream())
        .map(Employee::getName)
        .flatMap(name -> Optional.ofNullable(name).stream())
        .collect(Collectors.toList());
}

public interface UserRepository extends JpaRepository {
    Optional findByUsername(String username);
}

@GetMapping("/users/{id}")
public ResponseEntity getUser(@PathVariable Long id) {
    return userRepository.findById(id)
           .map(user -> ResponseEntity.ok(user))
           .orElse(ResponseEntity.notFound().build());
}

String timeout = Optional.ofNullable(config.get("timeout"))
                        .map(String::valueOf)
                        .orElse("30");

Optional.ofNullable(legacyMethodThatReturnsNull())...