Is @ParametersAreNonnullByDefault applies to method return values too?

Question

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.

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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. :)

Answer 1

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 {
}