No, you can’t write Jetpack Compose components in Java, and there are no future plans to allow this (source: I work on Compose). Note that this is not the same thing as using components created in Compose from a Java app, which is possible.
Jetpack Compose makes heavy use of Kotlin features such as coroutines, and @Composable methods require transformations that are done by a Kotlin compiler plugin. There is no way to get access to these from Java.