[JAVA] About the handling of Null

I think that many people may find null checking annoying when touching the development language. I think it's normal to see the existence of null objects, but to be honest, I think it's awkward to wrap even if you look at auto_ptr in C ++ / stl and Optional in java. Under such circumstances, I am very happy to try to eliminate null at the language level like kotlin.

So, I'd like to consider how to write code that does not encounter null, so I will write down what I care about for the time being

** Why do you hate null? ** **

The most disliked part of null is if (null === I think that the context is described as a context that has nothing to do with business logic. Therefore, I am thinking about how beautifully various people can be summarized only in business logic.

** Wrapping case as a common null avoidance method **

First, try collecting general null avoidance methods as far as you are interested

*** Return value of Collection ***

*** There is no need to perform null check like if statement, so there is no sense of discomfort in business logic *** List/Array/Map In SQL etc., if there is no data when getting the result, null may be returned. By using List, Array, etc. as the return value, null check can be eliminated or the number of items can be checked.

*** Optional *** and *** std :: auto_ptr ***

*** Instead of null check, substitute processing is inserted, but surrogate value can be entered in one statement, so the sense of incongruity in business logic is lessened *** std::auto_ptr In C / C ++, the operator operator can be used, so it can be used without discomfort depending on the application.

 int* pint = ptr.get();
```Etc., there is a problem of ownership etc. and it is necessary to pay attention to the implementation method

 Even though I want to use an object, it feels strange to call a method because it is wrapped.
 I've heard that it's always used only as a return value, but I think it's awkward to receive it as a return value and substitute it anew.

## *** Reactive Mono / Flux ***
 *** There is no need to perform null check like if statement, so there may be no discomfort in business logic ***
 It says "Issue one item at most", but intentionally wraps it with only 0 .. 1.
 It says "0 to N items" and intentionally represents 0 .. N.

# ** Cases where null conditions are not described, such as NullObject **
## *** Existence of exception and try / catch ***
 Recently, by using exception and try / catch, segmentation fault etc. caused by nullpo has disappeared, so it may be said that you do not have to worry about null object.

## *** If there is no exception ***
 When null check is not performed, memory leaks occur frequently and may cause unintended behavior.
 Therefore, it is necessary to perform appropriate error handling after null check.

 ***null object***
 When returning an object, returning a type other than object (null) will result in an unintended branch, but if a single object is returned, the logic can proceed smoothly.
 However, since it is necessary to return a reasonable behavior or exception in all methods, it may be more straightforward to throw a NullPointerException normally nowadays on the premise of try / catch.

Recommended Posts

About the handling of Null
About the description of Docker-compose.yml
About the behavior of ruby Hash # ==
About the basics of Android development
About error handling of comment function
About the role of the initialize method
Think about the 7 rules of Optional
Summary about the introduction of Device
About the log level of java.util.logging.Logger
About exception handling
About exception handling
About the version of Docker's Node.js image
What is testing? ・ About the importance of testing
About the operation of next () and nextLine ()
About the method
About the initial display of Spring Framework
About the error message Invalid redeclaration of'***'
About the treatment of BigDecimal (with reflection)
About the number of threads of Completable Future
About the package
About the mechanism of the Web and HTTP
[Java] Handling of JavaBeans in the method chain
Think about the combination of Servlet and Ajax
About the official start guide of Spring Framework
About the description order of Java system properties
About the idea of anonymous classes in Java
About next () and nextLine () of the Scanner class
Output about the method # 2
About the StringBuilder class
The world of clara-rules (2)
Commentary: About the interface
About Ruby exception handling
About disconnect () of HttpURLConnection
About the asset pipeline
About the function double-java
About selection of OpenJDK
About DI of Spring ①
About the ternary operator
Judgment of the calendar
The world of clara-rules (4)
The world of clara-rules (1)
null specifies the type
About DI of Spring ②
The world of clara-rules (3)
About the length method
About the Kernel module
The world of clara-rules (5)
The idea of quicksort
About the authenticate method.
About the map method
About the ancestors method
About form. ○○ of form_with
[Output] About the database
About @Accessors of Lombok
About the [ruby] operator
About the to_s method.
The idea of jQuery
[Grails] About the setting area and the setting items of application.yml
About the usefulness of monads from an object-oriented perspective
Talking about the merits of database bind variables ((1) Introduction)
About the problem of deadlock in parallel processing in gem'sprockets' 4.0