How to use Optional to check null values in java 8?

Question

I have a class containing nested and inner classes. And in some program, i am check for the null values of the object using equal operator in the legacy java way. The following is my code snippet:

class Outer {
    Nested nested;
    Nested getNested() {
        return nested;
    }
}
class Nested {
    Inner inner;
    Inner getInner() {
        return inner;
    }
}
class Inner {
    String foo;
    String getFoo() {
        return foo;
    }
}

And here is how i am doing the null checks on the reference variables:

Outer outer = new Outer();
if (outer != null && outer.nested != null && outer.nested.inner != null) {
    System.out.println(outer.nested.inner.foo);
}

I know this can also be done using the Optional class of java 8, but i am not getting a way for doing the same above particular scenario. Any suggestion?

KayV · Accepted Answer · 2016-12-07 12:19:11Z

8

The follwoing code worked well for me:

Optional.of(new Outer())
    .map(Outer::getNested)
    .map(Nested::getInner)
    .map(Inner::getFoo)
    .ifPresent(System.out::println);

answered Dec 7, 2016 at 12:19

KayV

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1 Comment

Eugene Over a year ago

and that's good code, you can totally answer your own questions here, even accept them. +1

dimitrisli · Accepted Answer · 2016-12-07 12:24:56Z

6

I highly suggest you watch the recent Devoxx Belgium presentation "Optional - The Mother of All Bikesheds" by Stuart Marks. Stuart is describing what was the initial intent, best practices and bad practices using it.

In particular using Optional in fields, quoting from the presentation slide:

Why Not Use Optional in Fields?

More a style issue than a correctness issue

use of Optional in fields often arises from slavish desire to eliminate nullable fields.

remember, eliminating nulls isn't a goal of Optional

Using Optional in fields..

creates another object for every field

introduces a dependent load from memory on every field read

clutters up your code

to what benefit? ability to chain methods?

To your example in particular:

why outer != null check? it's just got created!
if Nested instance needs to be part of Outer and Inner part of Nested have them part of the constructors and guard with some @NotNull code or check programmatically.

answered Dec 7, 2016 at 12:24

dimitrisli

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1 Comment

dimitrisli Over a year ago

Thanks for bringing such insight to the java community!

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