问题
The documentation for @ParametersAreNonnullByDefault says, that:
This annotation can be applied to a package, class or method to indicate that the method parameters in that element are nonnull by default unless ...
I don't consider a method's return type/value to be it's parameter. It is only part of its signature, so this is kind of ambiguous for me.
The Java tutorial for methods seems to think like me.
As Joachim Sauer pointed out for me in the comments section of his answer, the name @ParametersAreNonnullByDefault (parameters) should've clearly indicated for me that this annotation doesn't apply to methods' return types/values. I was blind! :) Thanks Joachim!
In light of this I can only says that an @EverythingIsNonnullByDefault should exist somwhere. :)
回答1:
I don't see a reason why @ParametersAreNonnullByDefault should apply to return values.
回答2:
No, @ParametersAreNonnullByDefault applies only to a method's parameters--the values it accepts from the caller (between the parentheses). The method is still free to return a null value.
Here's a class that combines all three places where you can apply @Nonnull, though in our code I still use three separate annotations, one of which is supplied by JSR-305.
package com.sample;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import javax.annotation.meta.TypeQualifierDefault;
/**
* This annotation can be applied to a package, class or method to indicate that all
* class fields and method parameters and return values in that element are nonnull
* by default unless overridden.
*/
@Documented
@Nonnull
@TypeQualifierDefault({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface EverythingIsNonnullByDefault {
}
来源：https://stackoverflow.com/questions/7658353/is-parametersarenonnullbydefault-applies-to-method-return-values-too