Using @NonNull with @Builder

[jilt3d]

I have the following class:

@Builder

public final class Foo {

    @NonNull

    private final String bar;

}

and the following test returns: java.lang.AssertionError: Expected exception: java.lang.NullPointerException

public final class TestFoo {

    @Test(expected = NullPointerException.class)

    public void shouldThrowNullPointerExceptionIfBarIsNull() {

        Foo.builder().bar(null);

    }

}

Do I miss something or @NonNull doesn't play with the @Builder?

[Reinier Zwitserloot]

This is on purpose.

Once you call the build() method, you'll get that exception. We intentionally allow you to set the field to 'null' in the builder, for a number of reasons:

* The builder's field cannot be called @NonNull, as it starts out as null. There is no practical way we can let you specify the initial value.

* It's a builder. The entire point of one is to be the context for the time between the thought of 'I want to make a complex object that has various prerequisites' and 'It is complete; I sign off on the requisites'. As you call methods on the builder, you're in the limbo state where the object is not valid. Throwing exceptions during this time is a bad idea as it's a known and workable state. For example, while this is reaching a little bit, you can call a set method on the builder to set the field back to null, as a way to say: Okay, right now I want any calls to build() to just fail, until someone remembers to actually set this to a valid value later.

Basically, update your test to expect the NPE when calling build().