Setup

swift4j is distributed as a Swift package. Add it as a dependency in your Package.swift and import the Swift4j product in any target you want to export to the JVM.

Package.swift

5.10

import PackageDescription

let package = Package(
    name: "MyLibrary",
    platforms: [.macOS(.v14)],
    products: [
        .library(name: "MyLibrary", type: .dynamic, targets: ["MyLibrary"])
    ],
    dependencies: [
        .package(url: "https://github.com/scade-platform/swift4j.git", branch: "main")
    ],
    targets: [
        .target(
            name: "MyLibrary",
            dependencies: [
                .product(name: "Swift4j", package: "swift4j")
            ]
        )
    ]
)

Two things to note:

• The library product must be .dynamic. The JVM loads native libraries at runtime using System.loadLibrary(), which requires a shared library (.so / .dylib).
• swift4j requires Swift 5.10 or later for macro support.

Importing in Swift

In any Swift file that uses the @jvm macro:

import Swift4j

That’s all the setup needed on the Swift side. The @jvm macro and the JNI runtime layer are both part of the Swift4j product.