Watch the collector retire data

1. static int retires() — create THREE distinct Object values, wrap each in a WeakReference, do NOT keep strong references, call System.gc() (twice, for reliability), then count how many weak refs return null from get(). 2. static int retiresWithStrong() — same three objects, but keep them in a static List<Object> pinned first; after System.gc() count nulls (expect 0 — strong refs are immortal while reachable). 3. static long heapAddress() — measure USED heap as totalMemory() - freeMemory() BEFORE and AFTER allocating int[1_000_000]; return the difference (after - before). Allocation shows up as used-memory growth.

Difficulty: advanced