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Wait, javas Optional is a reference type so it can be null? Doesn’t that almost defeat the purpose of it?

Defletter 3y ago
Yup. Your IDE will likely highlight it as an issue, but it's totally legal to return a null Optional. There's nothing special about it, it's just a wrapper class.
- alkonaut 3y ago
  Did the project to add value types to Java (I’m sure I heard of it a decade ago) never finish?
  - Defletter 3y ago
    Not yet, that's Project Valhalla iirc. It's coming along but hasn't been merged yet. I don't believe it's even a preview feature within the JDK yet.
  - steve_rambo 3y ago
    https://openjdk.org/projects/valhalla https://openjdk.org/projects/valhalla
michaelt 3y ago
Arguably yes, but that doesn't stop people using it. Basically Java had nulls from the start. A decade or so later some people who didn't like nulls introduced their own Optional type, as a third-party library. Enough people liked it that Optional was added to Java's standard library. But as it's just an object, it can be null. Some null avoidance enthusiasts also use third-party @Nullable and @NotNull annotations, which some automated code checking tools will attempt to verify during compile/test.
paulddraper 3y ago
Kinda. Every non-primitive is nullable in Java. Adding Optional doesn't/can't change that. You can have a gentlemen's agreement to prefer None to null.
pgwhalen 3y ago
It doesn’t defeat the problem in theory, but in my experience it does in practice. I’ve never come across an NPE on a nullable reference even in development - it would have to be the result of a really fundamental misunderstanding of the concept. YMMV. Obviously it depends on your teammates.
mrkeen 3y ago
It gives you the ability to treat nulls as something-to-fix. In a team without Optionals, every time you touch a null that you didn't expect, you have to decide "Is this deliberately null, or was it a mistake?" Without that knowledge, you don't know whether your code should assert against the null, or allow it to pass through as a valid value. With Optionals, it becomes much simpler to cut through that nonsense. A null is a bug and you fix it (with the exception of json at the boundaries of your system, etc.) If you do find a value where you change your mind about its nullability, changing it to/from Optional will give you compile errors in exactly those other parts of the code that you now have to check/change.

Yup. Your IDE will likely highlight it as an issue, but it's totally legal to return a null Optional. There's nothing special about it, it's just a wrapper class.

alkonaut 3y ago
Did the project to add value types to Java (I’m sure I heard of it a decade ago) never finish?
- Defletter 3y ago
  Not yet, that's Project Valhalla iirc. It's coming along but hasn't been merged yet. I don't believe it's even a preview feature within the JDK yet.
- steve_rambo 3y ago
  https://openjdk.org/projects/valhalla https://openjdk.org/projects/valhalla

michaelt 3y ago

Arguably yes, but that doesn't stop people using it. Basically Java had nulls from the start. A decade or so later some people who didn't like nulls introduced their own Optional type, as a third-party library. Enough people liked it that Optional was added to Java's standard library. But as it's just an object, it can be null. Some null avoidance enthusiasts also use third-party @Nullable and @NotNull annotations, which some automated code checking tools will attempt to verify during compile/test.

paulddraper 3y ago

Kinda. Every non-primitive is nullable in Java. Adding Optional doesn't/can't change that. You can have a gentlemen's agreement to prefer None to null.

pgwhalen 3y ago

It doesn’t defeat the problem in theory, but in my experience it does in practice. I’ve never come across an NPE on a nullable reference even in development - it would have to be the result of a really fundamental misunderstanding of the concept. YMMV. Obviously it depends on your teammates.

mrkeen 3y ago

It gives you the ability to treat nulls as something-to-fix. In a team without Optionals, every time you touch a null that you didn't expect, you have to decide "Is this deliberately null, or was it a mistake?" Without that knowledge, you don't know whether your code should assert against the null, or allow it to pass through as a valid value. With Optionals, it becomes much simpler to cut through that nonsense. A null is a bug and you fix it (with the exception of json at the boundaries of your system, etc.) If you do find a value where you change your mind about its nullability, changing it to/from Optional will give you compile errors in exactly those other parts of the code that you now have to check/change.