bring back javakit example

Author: ktoso

Sources/JavaKitExample/JavaKitExample.swift

@@ -0,0 +1,120 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import JavaKit
+import JavaRuntime
+
+enum SwiftWrappedError: Error {
+  case message(String)
+}
+
+@JavaClass("com.example.swift.HelloSwift")
+struct HelloSwift {
+  @JavaMethod
+  init(environment: JNIEnvironment)
+
+  @JavaMethod
+  func sayHelloBack(_ i: Int32) -> Double
+
+  @JavaMethod
+  func greet(_ name: String)
+
+  @JavaMethod
+  func doublesToStrings(doubles: [Double]) -> [String]
+
+  @JavaMethod
+  func throwMessage(message: String) throws
+
+  @JavaField
+  var value: Double
+
+  @JavaField
+  var name: String
+
+  @ImplementsJava
+  func sayHello(i: Int32, _ j: Int32) -> Int32 {
+    print("Hello from Swift!")
+    let answer = self.sayHelloBack(i + j)
+    print("Swift got back \(answer) from Java")
+
+    print("We expect the above value to be the initial value, \(self.javaClass.initialValue)")
+
+    print("Updating Java field value to something different")
+    self.value = 2.71828
+
+    let newAnswer = self.sayHelloBack(17)
+    print("Swift got back updated \(newAnswer) from Java")
+
+    let newHello = HelloSwift(environment: javaEnvironment)
+    print("Swift created a new Java instance with the value \(newHello.value)")
+
+    let name = newHello.name
+    print("Hello to \(name)")
+    newHello.greet("Swift 👋🏽 How's it going")
+
+    self.name = "a 🗑️-collected language"
+    _ = self.sayHelloBack(42)
+
+    let strings = doublesToStrings(doubles: [3.14159, 2.71828])
+    print("Converting doubles to strings: \(strings)")
+
+    // Try downcasting
+    if let helloSub = self.as(HelloSubclass.self) {
+      print("Hello from the subclass!")
+      helloSub.greetMe()
+
+      assert(helloSub.super.value == 2.71828)
+    } else {
+      fatalError("Expected subclass here")
+    }
+
+    // Check "is" behavior
+    assert(newHello.is(HelloSwift.self))
+    assert(!newHello.is(HelloSubclass.self))
+
+    // Create a new instance.
+    let helloSubFromSwift = HelloSubclass(greeting: "Hello from Swift", environment: javaEnvironment)
+    helloSubFromSwift.greetMe()
+
+    do {
+      try throwMessage(message: "I am an error")
+    } catch {
+      print("Caught Java error: \(error)")
+    }
+
+    return i * j
+  }
+
+  @ImplementsJava
+  func throwMessageFromSwift(message: String) throws -> String {
+    throw SwiftWrappedError.message(message)
+  }
+}
+
+extension JavaClass<HelloSwift> {
+  @JavaField
+  var initialValue: Double
+}
+
+@JavaClass("com.example.swift.HelloSubclass", extends: HelloSwift.self)
+struct HelloSubclass {
+  @JavaField
+  var greeting: String
+
+  @JavaMethod
+  func greetMe()
+
+  @JavaMethod
+  init(greeting: String, environment: JNIEnvironment)
+}