Nullable annotation usage

Question

I saw some method in java declared as   void foo  Nullable Object obj            What s the meaning of  Nullable here  Does it mean the input could be null   Without the annotation  the input can still be null  so I guess that s not just it

User · Answer

This annotation is commonly used to eliminate NullPointerExceptions. @Nullable says that this parameter might be null. A good example of such behaviour can be found in Google Guice. In this lightweight dependency injection framework you can tell that this dependency might be null. If you would try to pass null without an annotation the framework would refuse to do it's job.

What is more @Nullable might be used with @NotNull annotation. Here you can find some tips on how to use them properly. Code inspection in IntelliJ checks the annotations and helps to debug the code.

User · Answer

Granted  there are definitely different thinking  in my world  I cannot enforce  Never pass a null  because I am dealing with uncontrollable third parties like API callers  database records  former programmers etc    so I am paranoid and defensive in approaches  Since you are on Java8 or later there is a bit cleaner approach than an if block   public String foo  Nullable String mayBeNothing       return Optional ofNullable mayBeNothing  orElse  Really Nothing        You can also throw some exception in there by swapping  orElse to  orElseThrow    - gt  new Exception  Dont  send a null      If you don t want to use  Nullable  which adds nothing functionally  why not just name the parameter with mayBe    so your intention is clear

User · Answer

Different tools may interpret the meaning of  Nullable differently  For example  the Checker Framework and FindBugs handle  Nullable differently

User · Answer

It makes it clear that the method accepts null values  and that if you override the method  you should also accept null values   It also serves as a hint for code analyzers like FindBugs  For example  if such a method dereferences its argument without checking for null first  FindBugs will emit a warning

[java] @Nullable annotation usage

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