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When I looked among the standard constraints in Bean Validation API (JSR-303), I found the NotNull.List annotation. Its description is:
Defines several @NotNull annotations on the same element
This is valid syntax:
@NotNull.List({@NotNull, @NotNull})
private Object myObject;
But it makes no sense. Either the object is null or it is not. When would you use this annotation?
There are several other similar annotations like AssertFalse.List and AssertTrue.List.
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The @NotNull Annotation is, actually, an explicit contract declaring the following: A method should not return null. A variable (like fields, local variables, and parameters) cannot should not hold null value.
@NotNull The @NotNull annotation is, actually, an explicit contract declaring that: A method should not return null. Variables (fields, local variables, and parameters) cannot hold a null value.
@NotNull validates that the annotated property value is not null. @AssertTrue validates that the annotated property value is true.
@NotNull : The CharSequence, Collection, Map or Array object is not null, but can be empty. @NotEmpty : The CharSequence, Collection, Map or Array object is not null and size > 0. @NotBlank : The string is not null and the trimmed length is greater than zero.
Hi, when using the @NotNull annotation, IntelliJ will generate bytecode to throw an IllegalArgumentException when a null is passed/returned.
The @NonNull/@Nullable annotation can put in front of functions as well to indicate the return value nullability. return null; // warn: 'null' is returned by the method ... Easy, right? Keep your Billion Dollar in your pocket and enjoy using this @Nullable and @NonNull.
You can have multiple @NotNull annotations that are mutually exclusive based on the group attribute.
@NotNull.List({@NotNull(groups=Foo.class,message="Some message!"),
@NotNull(groups=bar.class, message="Some other message!"})
private Object myObject;
I do agree it's a little silly for this example since only the payload and message can be affected, but it's probably there to remain consistent with the other annotations.
See here for more details.
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