How to create a new object

JNIKit provides the JObject class, which holds a reference to a Java object.

Construct JObject with no arguments

Convenient way with clazz:

guard
    let clazz = JClass.load("com/mylib/mypackage/MyClass"),
    let object = clazz.newObject()
else { return }

More explicit way with env:

guard
    let env = JEnv.current(),
    let clazz = JClass.load("com/mylib/mypackage/MyClass"),
    let methodId = clazz.methodId(
        env: env,
        name: "<init>",
        signature: .returning(.void)
    ),
    let object = env.newObject(
        clazz: clazz,
        constructor: methodId
    )
else { return }

Construct JObject with arguments

Arguments have to be listed in both methodId and newObject in case of creating with env.

Let's assume a class constructor expects jint, jfloat, and jobject (which is java/lang/String).

Convenient way with clazz:

let object = clazz.newObject(
    123,
    1.23,
    "Hello" // or "Hello".wrap().signedAsString()
)

Explicit way with env:

let methodId = clazz.methodId(
    env: env,
    name: "<init>",
    signature: .init(
        .int,
        .float,
        .object("java/lang/String"),
        returning: .void // optional, .void by default
    )
)
let object = env.newObject(
    clazz: clazz,
    constructor: methodId,
    args: [
        123, // Int32 -> jint
        1.23, // Float -> jfloat
        "Hello".wrap()!.object // JObject -> jstring
    ]
)

The constructed object is now a JObject that holds a global reference to the instance and a global reference to its class. Keep this object for as long as you need it.

When JObject is deinitialized, its underlying jobject reference is released automatically.

⚠️ Do not delete the underlying jobject reference manually, and do not use jobject from JObject anywhere outside.