Theory

in java we can receive a gc notification by ReferenceQueue

when an object is recycled by jvm, Reference that hold it will be added to ReferenceQueue at the same time

so we can use Reference and ReferenceQueue to check whether an object is correctly released

Choose Solution

we choose WeakReference as the impl class, as it tells jvm to recycle object as soon as possible

we can call System.gc() to ask jvm for a gc execution, but this is not guranteed, it is just an advice

if you want trigger gc immediately, you can run a java command like this

jcmd <pid> GC.run

if you are running on an android platform, you can force a gc through Profiler tool

Profiler > New Session > Open Memory > Force Garbage Collection

Leak Check Tool

now let us achieve this tool

import java.lang.ref.ReferenceQueue
import java.lang.ref.WeakReference
import kotlin.concurrent.thread

object Leaker {

    class NamedWeakReference(obj: Any, val name: String) : WeakReference<Any>(obj, queue)

    private val queue = ReferenceQueue<Any>()
    private val refs = mutableListOf<NamedWeakReference>()

    init {
        thread {
            while (true) {
                Thread.sleep(1000L)
                val ref = queue.poll() as? NamedWeakReference
                if (ref != null) {
                    refs.remove(ref)
                    println("Leaker : ${ref.name} Recycled")
                }
            }
        }
    }

    fun add(obj: Any, name: String = obj.name()) {
        val ref = NamedWeakReference(obj, name)
        refs.add(ref)
    }

    private fun Any.name() = "${javaClass.simpleName}@${hashCode()}"
}

Appreciate The Masterpiece