How to keep null in Guava

Question

I am new to the Guava library.

I am trying to use an option in method arguments. One of the problems that I discovered is that I cannot pass null to Optional.

I think the purpose of introducing the Optional is to distinguish between

• Something that doesn't matter
• That which has a null value

For example, Optional.absent () means that the value does not exist. So far, null is a value.

With this logic, I assume that the option must have some way to allow us to store a null value in it. However, I could not find a way to do this.

My method is defined as:

void myMethod(Optional<String> arguments) { .... } 

If i use

 myMethod(Optional.of(null)); 

This will give me a runtime error that the value cannot be null.

How can I pass null inside optional?

Answer 1

I think this is an intentional limitation.

Optional is an implementation, possibly a monad . This is intended to replace zeros with a safe type, ensuring that if a parameter value is present, you will not get a NullPointerException when you try to use it. Permission to insert null will violate the type security guarantee.

If you really need to distinguish between two types of “no data” values, consider Optional<Optional<String>> instead (wrapping your internal possibly-zero data in Option<String> with Optional.fromNullable ).

Answer 2

See JavaDoc

An immutable object that may contain a non-zero reference to another object. Each instance of this type either contains a non-zero reference or does not contain anything (in this case we say that the link is "missing"); he never says contain null .

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Answer 3

Use Optional.fromNullable(T nullableReference)

Answer 4

From this wiki from google / guava repo, you should use

 Optional.absent() 

@ Dushan already wrote this in a comment on another answer, but I think it will be easier to find other people