Main.java

public final class Main {

    public static void main(String... args) throws Throwable {
        Integer i = new Integer(1);
        WeakReference<Integer> ref = new WeakReference<>(i);
        System.gc();
        System.out.println(ref.get());
        myStupidReachabilityFence(i);
    }

    private static void myStupidReachabilityFence(Integer i) {
    }
}

import java.lang.ref.WeakReference;