add jni sample app

Author: madsodgaard

Samples/JExtractJNISampleApp/src/main/java/com/example/swift/HelloJava2Swift.java

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+package com.example.swift;
+
+// Import swift-extract generated sources
+
+// Import javakit/swiftkit support libraries
+
+import org.swift.swiftkit.SwiftKit;
+
+public class HelloJava2Swift {
+
+    public static void main(String[] args) {
+        System.out.print("Property: java.library.path = " + SwiftKit.getJavaLibraryPath());
+
+        examples();
+    }
+
+    static void examples() {
+        MySwiftLibrary.helloWorld();
+
+        MySwiftLibrary.globalTakeInt(1337);
+        MySwiftLibrary.globalTakeIntInt(1337, 42);
+
+        long cnt = MySwiftLibrary.globalWriteString("String from Java");
+        SwiftKit.trace("count = " + cnt);
+
+        long i = MySwiftLibrary.globalMakeInt();
+        SwiftKit.trace("globalMakeInt() = " + i);
+
+        System.out.println("DONE.");
+    }
+}