A modern programming language that makes developers happier.

kotlinlang

what String! mean? File(uri).length, it shows me none of the following functions can be called with arguments supplied public constructor File(uri: URI!)

When type with ! like you said `String!`, it means the type with ! is came from another platform like java or groovy. It is called a platform type.

In java, there are no not null or nullable type, so you should choose binary option this platform type as not null type or nullable type.