Java优学网Optional类短文：告别空指针异常，用Optional优雅处理null值

// 一个实际的使用示例 String userInput = possiblyNullInput; String processed = Optional.ofNullable(userInput)

.map(String::trim)
.filter(s -> !s.isEmpty())
.orElse("默认值");

// 传统防御式编程 public String getUserCity(User user) {

if (user != null) {
    Address address = user.getAddress();
    if (address != null) {
        return address.getCity();
    }
}
return null;

}