Classes

Loading a class is the first thing you will face.

There are a few ways to load it.

Via env

let env = JEnv.current()!
let clazz: JClass = env.findClass("com/mylib/mypackage/MyClass")

This way you will use the system's class loader, which will fail loading your dynamically loaded class. It should be used only for fundamental classes like java/lang/Object.

Via classLoader

The goal is to retrieve the application's class loader, which has access to dynamically loaded classes.

In pure Java you could retrieve a class loader from any jobject, as was shown above in the initialize method.

In Android the class loader is available in ApplicationContext or ActivityContext, as well as in any jobject of course, but there is a shorter convenience getter like context.getClassLoader().

The usage is as simple as

let clazz: JClass = classLoader.loadClass("com/mylib/mypackage/MyClass")

Via cached instance

The preferred way is to use a convenience JClass method:

let clazz: JClass = JClass.load("com/mylib/mypackage/MyClass")

This way it tries to get it first from cache, then from the cached class loader, and if there is no cached class loader, then from the system's class loader.

Tip

You can call → static methods on the JClass type directly.

Class names

As you can see above, the class name is represented as a String, but actually it is not. The JClassName object contains the class name in all possible forms: dotted, slashed, and even just its pure name.

You can predefine classnames as constants in the code for easy reuse and typo safety:

let class1 = JClassName("com/mylib/mypackage/MyClass1")
let class2 = JClassName("com/mylib/mypackage/MyClass2")

and then pass it like this:

JClass.load(class1)

or even put it into a JClassName extension:

extension JClassName {
    static let class1 = JClassName("com/mylib/mypackage/MyClass1")
    static let class2 = JClassName("com/mylib/mypackage/MyClass2")
}

and then use it anywhere like this:

JClass.load(.class1)