feat: add basic rust JNI demo

rust-sandbox/.gitignore

@@ -0,0 +1,20 @@
+# Created by https://www.toptal.com/developers/gitignore/api/rust
+# Edit at https://www.toptal.com/developers/gitignore?templates=rust
+
+### Rust ###
+# Generated by Cargo
+# will have compiled files and executables
+debug/
+target/
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
+Cargo.lock
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+# MSVC Windows builds of rustc generate these, which store debugging information
+*.pdb
+
+# End of https://www.toptal.com/developers/gitignore/api/rust

rust-sandbox/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "rust-sandbox"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+name = "rustsandbox"
+crate-type = ["cdylib"]
+
+[dependencies]
+jni = "0.21.1"
+
+[target.'cfg(target_os = "android")'.dependencies]

rust-sandbox/src/lib.rs

@@ -0,0 +1,15 @@
+use jni::{
+    objects::{JClass, JObject},
+    JNIEnv,
+};
+
+#[no_mangle]
+pub extern "system" fn Java_net_mbess_popequer_Native_add(
+    _env: JNIEnv,
+    _class: JClass,
+    a: i32,
+    b: i32
+) -> i32 {
+    a + b
+}
+