I am using thirst party java library(stripe-java), and I am using Java FFI feature of fantom to call the API of this thirst party java library

There is this class in stripe-java library https://github.com/stripe/stripe-java/blob/master/src/main/java/com/stripe/param/ChargeCreateParams.java

which allows to create object using builder pattern

Now when I try to call a method setAmount(sys::Int) which accepts an Int fantom is giving me compiler time error even though I am passing Int

My Bad, setAmount() accepts Long

What does your compiler error look like?

The compiler error is as depicted in the screenshot:

Invalid args setAmount(sys::Int)

I can confirm this is an issue in Fantom 1.0.73:

using [java] com.stripe.param::ChargeCreateParams

...
ChargeCreateParams.builder.setAmount(150) // --> Invalid args setAmount(sys::Int)
...

The signature of setAmount() is:

public Builder setAmount(Long amount)

I can't think of any Java APIs off the top of my head that take java.lang.Long, so can't quickly test myself. But sys::Int? (nullable) is the same as java.lang.Long, so try casting it like this:

setAmount( (Int?)val )

//  or maybe this

Obj? boxed := intVal
setAmount(boxed)

It might just a that the compiler isn't auto-boxing in that case

setAmount( (Int?)val )

//  or maybe this

Obj? boxed := intVal
setAmount(boxed)

This worked, thanks Brian

It seems no java.lang.Long mapping. A fix like this

I pushed a fix for that allow Fantom types to be used directly for their Java counterparts:

java.lang.Bool -> sys::Bool?
java.lang.Long -> sys::Int?
java.lang.Double -> sys::Float?