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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!)

<https://kotlinlang.org/docs/reference/java-interop.html#null-safety-and-platform-types|https://kotlinlang.org/docs/reference/java-interop.html#null-safety-and-platform-types>

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.